Coastal Theory Interactive (Archive)

Overview

Definitions on Earth

General 1

We presume that the earth is a perfect sphere and is the center of the universe. The earth is rotating round a hypothetical axis "P P1" and is penetrated in two points. The upper point "P", is called the North Pole and the lower point "P1", is called the South Pole. "P" and "P1" are known as the Geographical poles. "K" is the center of the earth. Any plane passing through the center "K" is known as a Great Circle Plane. The circumference of the great circle that is right angled to the hypothetical axis "P P1" is called the Equator, and divides the globe or sphere into two equal hemispheres, the northern hemisphere where the North Pole is located, and the southern hemisphere where the South Pole is located. The circumference of the small circle "A A1" with a plane parallel to the Equator is called the Parallel Latitude.

General 2

The circumference of the Great Circle that includes the hypothetical axis "PP1" (therefore the geographical poles) is called the Meridian. Therefore the "PP1P" is a Meridian. The Meridian Planes intersect at the axis of the earth. The meridian that passes from Greenwich is called the Prime Meridian or Meridian of Greenwich and divides the earth into two hemispheres: the hemisphere lying east of the Atlantic that includes Europe, Asia, Africa and Australia, called the Eastern Hemisphere, and the other half lying west of the Atlantic that includes North and South America, called the Western Hemisphere. To define a location (position) on the surface of the earth (except the poles), we use Geographical coordinates. As a base and starting point for these coordinates we rely first on the Equator, and second the Prime Meridian. The coordinates are the Geographical Latitude (latitute) and the Geographical Longitude (longitude).

Latitude

From a position “L” on earth, only one parallel and one meridian pass through. The Geographical Latitude of position “L” is the arc on the meridian, (passing from "L"), that is included between the Equator and the parallel passing through "L". The latitude is defined as North (N), if the position is in the northern hemisphere, or South (S), if the position is in the southern hemisphere. The latitude is measured in degrees, minutes,and seconds, starting from 0 degrees at the equator, up to 90 degrees North (N) or 90 degrees South (S). Every degree has 60 minutes and every minute has 60 seconds.

Longitude

The Geographical Longitude of position “L” is the arc on the Equator that is included between the Prime Meridian and the Meridian passing through “L”. The longitude is defined as East (E), if the position is in the eastern hemisphere, or West (W) if the position is in the western hemisphere. The longitude is measured in degrees, minutes and seconds, starting from 0 degrees at the Prime Meridian, up to 180 degrees East (E) or 180 degrees West (W). As with latitude, every degree has 60 minutes and every minute has 60 seconds.

Navigational terms

Here are some important navigational terms. You should know these in order to understand navigational data and minimise the risk of missunderstandings. Degrees True (T) stands for direction or bearing that is relative to true north. For example 090° T(rue). Degrees magnetic (M) stands for direction or bearing that is relative to magnetic north. For example 260° M(agnetic). No correction for variation has been applied. Degrees compass (C) stands for direction or bearing that is meassured by the compass. For example 123° C(ompass). No correction for variation and deviation has been applied. Variation stands for the angular difference between Magnetic North and True North. Deviatoin stands for the difference between a compass reading and a magnetic reading, caused by the magnetic fields on the boat. Knot stands for the unit of speed used at sea. 1 Knot is 1 Nautical Mile per hour. You can either say that the boat´s speed is 1 Knot or 1 Nautical Mile per hour. Nautical Mile stands for the unit of distance at sea. It is based on the cirumference of our planet. 1 Nautical Mile is 1852 meters/6076 feet, or 1 minute of latitude. 1 Nautical Mile is divided into 10 cables. 1 cable is 185 meters/200 yards. Dircetions at sea, for example a landmark, are expressed in degrees. They are measured clockwise and are relative to True North.

Nautical Charts

General

In this lesson we will learn about Nautical Charts. A Nautical Chart is a graphic representation of the marine environment and is essential for safe navigation. The Mariner uses the Nautical Chart to navigate and as a worksheet. Using the Chart, the mariner lays out courses and navigates the ship safely by the shortest and most economical route. On a Nautical Chart we can observe: the Latitude and Longitude scale. the form and nature of the coast, the depths of the water and composition of the sea bottom, locations of dangers to navigation, we also see locations of man-made aids to navigation, the characteristics of the Earth's magnetism, Tidal information and much more. We will study all of these individually.

General

Projection is the process of flattening a three dimensional surface to form a plane. In other words, it is the representation of the surface of the earth as a flat surface. Different projections have been developed for transferring information from a sphere to a plane, and each distorti the data in different ways. The projections are: First, the Conic projection which includes the Simple conic projection, the Lambert conformal projection and the polygonal projection. Second, the azimuthal projection which includes the gnomonic, the stereographic and the orthographic projection. And third, the cylindrical projection which includes the Mercator, the transverse and the oblique Mercator projection.

Mercator Projection

The Mercator projection is the most common projection used in marine navigation. On a Mercator chart: The lines of latitude and lines of longitude remain parallel and they cross each other at right angles. The directions can be accurately plotted, and a course can be plotted from one point to another, making it possible to sail along that line (this is called the Rhumb Line) by steering a single compass course. The Rhumb Line crosses all meridians at the same angle. The shape of an object is accurately represented. Sailing towards the poles, the objects appear larger than they actually are.

Introduction

Viewing a nautical chart for the first time can be very challenging. It can seem complicated if you don't know what you are looking at and what it means. Things you should take notice of when looking at the nautical chart are: The title block where you can see the crest, which is located at the top of the chart title and will ensure your chart is official. The main title, which states the specific geographic area of the chart. The nautical scale identification. “Natural Scale” means the relationship between the size of the chart and the earth), where the scale gives an indication of how detailed the chart is.

Types and scales

Here are the different types and scales of charts: Sailing charts, where the scale is 1:500,000 and smaller, are used for offshore navigation beyond sight of land. The general charts have a scale of 1:150,000 - 1:500,000, and give wide-ranging offshore coverage with sufficient inshore detail to make landfall sightings easy. Fisheries charts use these scales. The coastal chart uses a scale of 1:50,000 - 1:150,000, and are used to show uninterrupted wide-ranging coverage with adequate inshore detail to make landfall sightings easy. Fisheries charts also use these scales. The approach chart has a scale of 1:15,000 - 1:50,000, and are used for approaching coasts where great detail is required. Harbor charts, which have a scale is1:5,000 - 1:15,000, are used for navigation in harbors or intricate, hazardous, shoal-infested waters. Bar Scales: a bar scale is a graphic scale represented by a line or a bar that is subdivided into nautical miles, feet, or meters. This bar is used for measuring distances on the chart. Elevation Contours: lines connecting points of equal elevation. It's a graphic way of showing the shape and slope of hills and mountains that might be helpful in identifying them on the chart. Once identified, it can help identify your location on the water.

Depth note

Other things you should take notice of when looking at the nautical chart are: The depths note, which indicates what units of measurement are used to indicate the depths on the chart. You may read SOUNDINGS IN FATHOMS AND FEET or SOUNDINGS IN METERS. Sounding in fathoms and feet indicates that soundings are in fathoms with subscript in feet. The larger number indicates fathoms, and the small number indicates feet. For example, you see a spot depth of 34. This indicate a depth of 3 fathoms and 4 feet, or 22 feet, as one fathom is six feet. Sounding in meters indicates that soundings are in meters and decimeters. For example you see a spot depth of 76. This indicate a depth of 7 meters and 6 tenths of a meter. You can convert between meters, feet and fathoms by using the depth conversion table provided on the chart. The depths indicated on the chart are reckoned from the chart sounding datum. That could be the Mean Lower Low Water, or the Mean Low Water, or other tidal datum. To avoid grounding you have to take into consideration the height of tide and the tidal range.

Number-Elevation-Notes

Other things you should take notice of when looking at the nautical chart are: The chart number. The chart numbers differentiate charts of the same area. Elevations note, which describes the datum used to indicate the clearance of bridges and overhead cables and the elevation of constructions. Notes and warnings In the title block you may find notes and warnings concerning the nautical chart. By reading them carefully you will decide if they are applicable to your voyage. Datum note This datum note may reed “ WGS-84 (World Geodetic System 1984)" , “WGS or "Positions obtained from satellite navigation systems referenced to the WGS-84 can be directly plotted on this chart.". It is crucially important that your GPS be set to use the datum of the chart you are using! Chart corrections and edition In the bottom left corner of the chart you will find the chart corrections by year and number, which were applied on the chart. Corrections are published several times a year in the notices to mariners. Chart Abbreviations and symbols. There is a book named Chart Abbreviations and symbols, where you may find an entire index of abbreviations, a key to all of the chart symbols, and an explanation of the IALA buoyage system. In addition you may find general features, topography, hydrography and aids to navigation.

Natural features

Looking at the navigation chart we can see lots of symbols and abbreviations. Each Symbol and Abbreviation on the navigation chart has a meaning, representing a shorthand way of covering significant information. The knowledge and understanding of those symbols and abbreviations are crucial for safe navigation. On the nautical chart you will see: Natural features including coastline, relief, water features,vegetation and supplementary national symbols.

Cultural features

On the nautical chart you will also see: Cultural features including: settlements, buildings, roads, railways, airfields and other cultural features. Landmarks including: factories, churches, temples, monuments, tanks and forts.

Control Points - Magnetic compass

On the nautical chart you will also see: Control points including: observation spot and benchmark. Symbolized positions including: accurate position, candela and knot. Magnetic compass including: compass rose, variation, annual change, magnetic variation curves, local magnetic anomalies.

Ports

On the nautical chart you will also see: Ports, including: port structures,harbor installations, moles, dolphins,dry docks and canals. Tides and currents including: tidal levels, charted data, tide tables, tidal streams and currents.

Depths and dangers

On the nautical chart you will also see: Depths including: soundings,depths in fairways and areas, depth contours, types of seabed and intertidal areas. Dangers including: rocks, wrecks and obstructions.

Offshore installations - Tracks and routes

On the nautical chart you will also see: Offshore installations, including: platforms, moorings, underwater installations, submarine cables, submarine pipelines, tracks and routing measures. Track and routes including: radar surveillance system, radio reporting points, routing measures.

Areas and Limits - Fog signals

On the nautical chart you will also see: Areas and limits including: anchorages, anchorage areas, restricted areas, military practice areas, international boundaries, national limits and other various limits. Fog signals including: various types of fog signals with abbreviations.

Lights

On the nautical chart you will also see: Lights, including: light structures, major floating lights, light characters, color of lights, period, elevation, range, disposition, leading lights, lights in line, direction lights, sector lights and lights with limited times of exhibition.

Electronic position fixed system

On the nautical chart you will also see: Electronic position fixed systems including: radar, radio and loran-C. Services including: pilotage, coastguard, rescue and signal stations.

Nautical publications

To navigate safely, you need to have reference books that provide detailed information on tides, radio and light signals, symbols, etc. The principle books are: 1. Nautical Almanac 2. Pilot Books 3. Tide Tables 4. Tidal Atlases 5. Lights and Fog Signals 6. Radio Signals 7. Symbols and Abbreviations Let’s have a closer look at these books. The Nautical Almanac is updated every year, so you need a current copy. The Almanac provides you with astronomical information, tide information, meteorological information and more. Pilot Books amplify information on charts. For example, detailed harbor, approach, and caution information. Tide Tables provide you with detailed information on tides in each port. Tidal Atlases provide you, in pictorial form, the direction and rate of the tidal stream. Lights and Fog Signals give you detailed information about lights, light structure, light-vessels and so on. Radio Signals give you worldwide radio information, for example: Coast Radio Stations, Search and Rescue Procedures, Medical Advice by Radio, and so on. Symbols and Abbreviations provide you with detailed explanations of symbols and abbreviations that are used on charts.

Chart correction

On a Nautical Chart, features such as buoys, channels, wrecks, and so on can be omitted or their positions changed. Therefore, a nautical chart should be kept up to date. Published corrections are issued regularly from the relevant chart authorities. New charts are issued periodically. You can correct the charts yourself or a chart agent can correct them.

Chart Symbols

This is an interaction - have fun!

Plotting tools

Use of the parallel ruler 1

The Parallel ruler is used to draw lines and plot directions on a nautical chart. In addition, it allows courses to be measured from a convenient meridian. The ruler is split in half and the two halves are joined together by pivot points with aluminum arms and handles. Usually they are made of extra strong, crystal clear acrylic.

Use of the parallel ruler 2

Looking at the nautical chart, lets assume you are departing from point A and you want to arrive at point B. To determine the direction or the true course to follow from A to B, follow these steps: First, connect the two points A and B with a straight line and make sure that the course you want to follow is clear from navigation hazards and obstructions. Second, line up the parallel ruler with the two points A and B. Third, move the parallel ruler, by alternating the halves, holding down one half by the handle and moving the other half, repeatedly, until you reach the nearest compass rose.

Use of the parallel ruler 3

Steps to determine the direction or the true course, continued. Fourth, place one side of the parallel ruler in the center of the compass rose. As you can see from the example, you have two readings, 110° and 290°. To find which course to use, 110° or 290°, imagine that you start point A in the center of the compass rose, so that point B will then show the direction and therefore the correct reading. In your case, point A is at the center of the compass rose and point B shows the direction, therefore the reading of 110 degrees. In contrary, if you depart from point B and you want to arrive at point A, following the previous example, you should follow a true course of 290 degrees.

Introduction

The divider is used to measure or transfer distances on the nautical chart, using the latitude scale. In other words, it is used to “walk off distances on the chart”. Distances at sea are always measured in nautical miles. One degree of latitude is equal to 60 minutes, and one minute is equal to sixty seconds. One minute of latitude is equal of 1 nautical mile, 1852 meters or 6076.11 feet Before you measure any distance, look at the scale of your chart. In this example the scale is in degrees and minutes. To measure a distance, always use the latitude scale, located in the same parallel from where you want to measure. Do not use the longitude scale.

Measuring distance 1

How do you measure a distance using the divider? Let’s assume you sail from point A to point B. The true course is 110°, and you want to find how many nautical miles it is from A to B. In other words, the distance from A to B. Place one leg of the divider at point A and the other leg at point B. Next apply this span on the latitude scale which is closest to points A and B. Read the scale to find that the distance is 10 minutes or 10 nautical miles.

Applying a meassured distance

How do you apply a measured distance using the divider? Let’s assume you calculate a distance of 10 miles, and you want to apply it in your true course starting at point A, assuming your true course is 110 degrees. Use the divider and span a distance of 10.5 miles on the latitude scale which is closest to point A. Apply this span on your course, placing one leg of the divider at point A and the other leg on the course, marking the new position B. We can see that the distance from A to B is 10.5 nautical miles.

Measuring distance 2

How do you measure a distance that is longer that the span of your divider? Assume that you sail from point A to point B. The true course is 110°, and you want to know how many nautical miles it is from A to B. However, the distance to be measured is greater than the divider’s span. Use the divider and span a distance of 10 miles on the latitude scale which is closest to point A and B. Walk the divider along the course as many times as needed until you get close to point B, and mark the last point as point X. In our case we need to walk the divider three times. That makes 3 times 10 miles, equalling 30 miles. Now measure the distance from point X to point B and apply this span on the latitude scale which is closest to point B. On the scale you find that in this case the distance is 4 minutes or 4 nautical miles. So the distance from A to B is 34 nautical miles

Magnetic Compass

Application of variation 1

True North is the direction toward the Geographic North Pole. On a nautical chart, all lines of longitude are aligned to the True North. Magnetic North is the direction toward the Magnetic North Pole. The angular difference between True North and Magnetic North is called the Magnetic Variation, which changes very slightly each year and varies at different locations on earth. Magnetic Variation is listed on the chart as east or west. When variation is listed as east, then the Magnetic North is east of the True North and when variation is listed as west, the Magnetic North is west of the True North.

Application of variation 2

On every nautical chart there is at least one Compass Rose. The Compass Rose consists of the following: the outer rose, which is aligned with the True North and the inner rose, which is aligned to the Magnetic North. Near the center of the Compass Rose we can read the local variation, the year that the variation was observed and the annual rate of change. When we are shaping a course or plotting a position we need to convert between True and Magnetic.

Application of variation 3

On a nautical chart, to convert a True Course to a Magnetic one, or to convert a True Bearing to a Magnetic one you must apply the following formula: From True to Magnetic, add the Westerly Variation and subtract the Easterly Variation. To convert a Magnetic Course to a True one, or a Magnetic Bearing to a True one you must apply the following formula: From Magnetic to True, subtract the Westerly Variation and add the Easterly Variation.

Application of variation 4

Your True Course is 020 degrees and the Magnetic Variation for the year of 1993 is 6 degrees and 00 minutes West. The annual rate of change is increasing 7 minutes, your task is to calculate the Magnetic Variation for the current year, and to find your Magnetic Course. First calculate the correction of the Magnetic Variation for the current year, in your case 2002. Apply the following formula: Correction for the current Year = (current Year - Variation observed year) x Annual rate . That means the correction for the current Year = (2002 - 1993) x 7 = 63 minutes or 1 degree and 3 minutes (increasing). Secondly, calculate the Magnetic Variation for the current year using the following formula: Magnetic Variation for the current year = chart Magnetic Variation +/- correction for the current year. We use + when the correction for the current year is increasing. We use - (minus) when the correction for the current year is decreasing. That means the Magnetic Variation for the current year is 6 degrees 00 minutes + 1 degree and 3 minutes, which = 7 degrees and 3 minutes west. Thirdly, convert the True Course to a Magnetic one, using the formula:True to Magnetic: add Westerly Variation and subtract Easterly Variation. That means the Magnetic course is 020 degrees + 7 degrees and 3 minutes, which = 27 degrees and 3 minutes.

Application of deviation 1

The difference between the direction of Magnetic North and the direction that the compass points to is known as Magnetic Deviation. Compass deviation is caused by the environmental influences on your compass. On the boat, it can be influenced by electrical equipment, metal objects and magnetic fields. Large errors can occur on westerly and easterly courses, while there may be little or no error on northerly or southerly courses. Deviation varies at each compass point. If a deviation on your boat exists, it is important to create a Deviation Card. The card provides the data needed for course correction. On any course, the deviation should not exceed 6 degrees

Application of deviation 2

Use your Deviation Card to convert between Magnetic and Compass Courses. To create a Deviation Card, steer an accurate course of due North (000 degrees compass). Take a hand bearing compass to sight along the centerline of the boat and position yourself at the stern, clear of any possible interferences. Note down the course steered and the reading from the hand bearing compass. In our case the course steered is 000° and the reading from the hand bearing compass is 002 degrees, alter the course to 030 degrees compass and repeat the procedure. For the second reading the course steered is 030° and the reading from the hand bearing compass is 033°. Complete a 360 degree turn, noting your Compass Course and the reading of the hand bearing compass for every 30 degrees alternation. As you complete the readings, note in the center of the Deviation Card your Compass Courses - 0 degrees, 30 degrees, 60 degrees and so on. Then on the relevant Compass Course note the respective hand bearing observations. On the right side, mark the easterly variation and on the left side the westerly.

Application of deviation 3

In the previous lessons you learned to calculate the Magnetic Variation and also to find out the Magnetic Deviation by using the Deviation Card. Let's assume that the True Course plotted on the chart is 020 degrees, the Variation is 3 degrees West and the Deviation is 5 degrees East. To find out the Magnetic Course, proceed as follows

Application of deviation 4

Let's assume that your boat is on a Compass Course of 018 degrees, and you want to convert the course to a True Course so you can plot it on the chart. The Deviation is 5 degrees East and the Variation is 3 degrees West. To find out the True Course for plotting, follow these steps: First apply the Deviation to your Magnetic Course, using the formula: Compass to Magnetic add Easterly, subtract Westerly. In our case 018 degrees Compass plus 5 degrees East Deviation equals 023 degrees Magnetic. Secondly, calculate your Magnetic Course using the formula: Magnetic to True subtract Westerly Variation and add Easterly. In our case 023 degrees Magnetic minus 3 degrees Variation equals 020 degrees True. Thus, the Magnetic Course is 018 degrees, and the True Course you have to plot on the chart is 020 degrees. Follow the same method if you want to convert a Compass Bearing to a True Bearing.

Use transits to check compass error

Transits are not only used to determine your position line, they can also be used to check your compass error. On your chart, look for two objects in line. As you already know, transits can be man-made objects or natural ones. So, the two objects can be two beacons, two buoys, a building and a light house, or other objects. With your parallel ruler, determine the True Bearing of the transit and make a note of it. In this case the True Bearing is 115 degrees. Now point the bow of your boat towards the two objects. When they come in transit, make a note of your Compass Bearing, which in this case is 120 degrees. As the Compass Bearing is more (best) than the True one, the error is West. To memorize that, remember: Compass best error West, Compass least error East. To find the error, subtract 120 degrees Compass from 115 degrees True). The Error of our compass is 5 degrees West.

Steering compass 1

Your boat should be equipped with a good quality steering compass. There are two types of steering compasses: the conventional compass and the fluxgate compass. The conventional compass has two or more magnets attached to the underside of the compass card. The card is mounted above the magnetic needle mechanism on a pivot. To slow down the rotation of the card, it is dampened with a liquid. The housing is either of glass or plastic. As the boat turns, the compass aligns with magnetic north and south. The course to steer is read against the lubber line. The fluxgate compass is equipped with cards, pivots, liquids and a digital readout. It uses an electronic circuit to sense the lines of magnetic force. Fluxgate compasses should be kept level, otherwise major readout errors may occur.

Steering compass 2

When mounting a steering compass in a boat, be aware of the following recommendations: 1.the compass must be mounted with the lubber line on the boat’s fore-and-aft line 2.the compass must be mounted so as to be seen easily by the helmsman To avoid deviation problems, don’t mount the compass close to large metal objects. Mount the compass at least 2 meters (6 feet) away from the engine.

Hand held compass

A hand held compass is used to obtain compass bearings on shore or floating objects. Simply line up the lubber line with the object and read off the degrees. When using a hand-bearing compass keep it away from metal objects and steel-rimmed eyeglasses, and keep it leveled. Brace yourself in a secure position and away from too much ship movement.

Shaping the Course

How to shape a course

Let’s assume, you want to sail from A to B, and A is the departure point while B is the arrival point. Using a ruler and a pencil, draw a line connecting the two points, this is the course you have to follow over the ground to arrive at point B, and this is called the ground track. Usually we mark this track with two arrowheads. The next and very important step is to check that the course you draw is clear of hazards. Now you have to find out how many nautical miles it is from A to B. In other words, the distance. Using your divider you find that the distance from A to B is16 nautical miles. Let’s assume that your anticipated speed is 8 nautical miles. Dividing this distance figure, 16 nautical miles, by the anticipated speed, 8 nautical miles, you will find the duration of the voyage from A to B, in your case is 2 hours. Assuming you depart from point A at 0800 hours, your ETA (Estimated time of arrival) will be 2 hours later, 1000 hours. Using the parallel ruler you find that the course to steer is 045 degrees true or compass. No wind or tidal stream has been taken into account.

Allowance for leeway 1

Taking into account the tidal stream or the current, another factor has to be added: the wind. When you experience strong winds from abeam, you will have to allow for leeway. Leeway is the sideways movement of the boat caused by either wind or current. To estimate your leeway angle, take a bearing on the wake of your boat using the hand bearing compass. Compare this bearing with the reciprocal heading. The difference is the leeway angle.

Allowance for leeway 2

For example, your boat has a compass heading of 090 degrees, so it follows that the reciprocal heading is 270 degrees - 090 degrees plus 180 degrees. The reading of the hand bearing compass is 265 degrees. The difference between 270 and 265 is 5 degrees. Your leeway angle is 5 degrees. Having the wind from the starboard side, you have to add the leeway angle - 5 degrees, to your compass heading - 090 degrees. To offset the effect of the wind on your boat, your compass heading must be 095 degrees. Memorize the following rules: wind from port side: water track minus leeway angle = course to steer. Wind from starboard side. water track plus leeway angle = course to steer.

Allowance for tidal streams 1

For example, let’s assume that our ground track is 045 degrees true, and our sailing speed is 8 nautical miles per hour. With the divider we span a distance of 8 nautical miles on the latitude scale. We apply this span placing one leg on point A and the other leg along the ground track and name this point B. We mark the ground track with 2 arrowheads. Note: we use 1 arrowhead for the indication of a water track, 2 arrowheads for a ground track and 3 arrowheads for the tidal stream or current. Now we check the Standard Port to which the tidal streams are referred to. On the chart we find out that it is "Portsmouth". With this information we enter the tide table. We are interested in the morning High Water. The morning High Water on September 2nd is at 10:39 and the height is 4.3 meters. To find out whether the rate of the tidal stream is a spring or a neap rate, we also have to take the height of the preceding Low Water into account, which is 0.1 meters. To calculate the tidal range at this time we subtract the High Water from the Low Water. Consequently the tidal range is 4.2 meters: 4.3 minus 0.1 meters.

Allowance for tidal streams 2

Let’s now consult the "Tidal Levels Table" which is located on the chart. As we can see, the spring tidal range in Portsmouth is 4.4 meters high, MHWS (Mean High Water Springs), 4.4 meters minus MLWS (Mean Low Water Springs), 0.0 meters - equals 4.4 meters. We now know that the rate of the stream is close to a spring rate, because the tidal range on September 2nd is 4.2 meters. With this data we can enter the Tidal Stream Table, also located on the chart. First we have to find out which tidal diamond is closest to our ground track. The nearest tidal diamond is "A". Now, we select either the hours before High Water or after High Water. Let’s assume that we want the set and the drift 2 hours before high water, i.e. for 08:39 hours. Following the same line we read that the direction of the tide - the set, is 115 degrees, and the spring rate - the drift, is 2.3 knots.

Allowance for tidal streams 3

To apply the set of 115 degrees to our ground course, we place the parallel ruler on the 115 degree line on the compass rose and then transfer this line to point “A”. With the divider we span 2.3 nautical miles at the latitude scale. Then we place one leg on point “A” and the other leg along the tidal set and mark this point with “C”. Mark the line with three arrowheads in the direction of the set. Now we join together points “C” and “B”. The line from “C” to “B” is our water track. Mark the line with a single arrowhead. Now we transfer the parallel ruler to the compass rose and read off the degrees. The true course to steer to point “B” is 030 degrees. This course is required to offset the effects of the tide in one hour. Don’t forget to convert from True Course to Compass Course!

Dead Reckoning

Dead reckoning

When we are on an open sea passage out of sight of land, at night or in a dense fog, we must be able to keep an accurate track of our position and course at all times. There are many ways we can do this, and many techniques we can use for finding our position. The most basic technique is called the Dead-Reckoning Technique. Let’s assume that we are sailing from A to B, and that A is the last fixed position plotted on the chart at 10:00. Now it is 11:30 and we have to plot a new position using the Dead Reckoning (DR). The true course is 045 degrees, and the speed through the water, taken from the speed log is 7 nautical miles per hour. Knowing the course, the speed, and the running time from 10:00 am to 11:30 am, we can find the distance sailed using the formula - D is equal to S times T divided by 60, where D is the distance in nautical miles, S is the boat speed, and T is the time in minutes. In our case: 7 knots times 90 minutes divided by 60 equals 10.5 nautical miles. Using the divider, we span a distance of 10.5 miles on the latitude scale which is closest to the course line, and which runs along the sides of the chart. We applied this span on our course, placing one leg of the divider on the 10:00 position and the other leg on the course, marking the new position with an X, recording the time of 11:30am.

Estimated position

If we apply the set and the drift of the tide to the 11:30 Dead Reckoning (DR) position, we will have converted this position to an 11:30 Estimated Position (EP). To work out the set (direction) and the drift (speed) of the tide, we refer to the tidal diamonds on the nautical chart, or to the tidal stream atlas. Let's assume that at that time the set is 110 degrees, which means that the direction of the tide is towards 110 degrees, and the drift is 3 nautical miles/per hour(knots). To apply the set (direction) of the tide on the 11:30 Dead Reckoning (DR) position we place the parallel ruler on the 110 degree line of the compass rose and transfer that line to the DR position. To apply the drift (speed) of the tide on the 11:30 Dead Reckoning (DR) position to our time frame we use the formula: D is equal to S times T divided by 60, where D is the distance in nautical miles, S is the tide speed, and T is the time in minutes. In our case: 3 knots times 90 minutes divided by 60 equals 4.5 nautical miles. Using the divider, we span a distance of 4.5 miles on the latitude scale which is closest to the course line and which runs along the sides of the chart. We apply this span, placing one leg of the divider on the 11:30 DR position and the other leg on the 110 degrees tide set, marking the new position with a triangle, recording the time as 11:30. This is our 11:30 Estimated Position (EP). Using the parallel ruler, we transfer the 045 degrees course to the new 1130 Estimated Position, and from there we continue to plot our new positions.

Position fixing

Introduction

The major concern of the navigator while navigating near the coast or off-shore to the open sea, is to determine his position as accurately as possible. So far, you have learned about the Dead Reckoning and the Estimated Position. In this lesson you will learn about Line of Position (LOPs), Running Fix position and Fix position. You will also learn about electronic fixes, fixes containing a mixture of position lines and ranges by dipping distances.

Introduction 1

Line of Position (LOPs) Line of Position LOP is the locus of points along which a ship's position must lie. A line of position can be obtained by: Visual Range, Visual Bearing and Distance.

Introduction 2

The Visual Range LOP is the most precise and reliable LOP, since it is not dependent on a device such as compass or radar. This LOP can be obtained by observing two objects in line such as two buoys, or an island and a buoy, or two predefined buildings, and then connecting the two objects with a straight line. Somewhere in this line is the ship’s position.The Visual Bearing LOP, can be obtained by taking a bearing using the hand held compass. Then, the information can be plotted on the chart after converting to a True Bearing. The Distance LOP or Range LOP can be obtained either using the radar or the sextant by taking horizontal angle. Using the measured distance as radius we draw a circle around the object. The ship must be somewhere on this circle.

Introduction

In this lesson we will learn about the Running Fix Position. Sometimes only one object is available for taking LOPs, for example a single buoy, a small island or rock, a radio tower and in celestial navigation during daytime, the sun. The Running Fix is a method of obtaining the ship’s position by taking more than one LOP from the same object at different times, taking into consideration the vessel’s speed.

Plotting

This is how we plot a Running Fix Position: Assuming the course is 080° degrees and the speed is 8 knots, or 8 nautical miles per hour, we take a bearing of 045° degrees on Alfa rock at 0900, now convert the compass bearings to true bearings and we plot it on the chart. After 30 minutes we take a new bearing on the same rock that reads 015°degrees, now convert the compass bearings to true bearings and plot it on the chart along with the new time - 0930. Knowing the speed, the next step is to determine the distance that the vessel sailed from 0900 to 0930. For that we use the formula: D is equal to S times T divided by 60, where D is the distance in nautical miles, S is the boat speed, and T is the time in minutes. In our case: 8 knots times 30 minutes divided by 60 equals 4 nautical miles. Using the divider, we span a distance of 4 miles on the latitude scale which is closest to the course line, and which runs along the sides of the chart. We applied this span on our course, placing one leg of the divider on the 0900 LOP intercepting the course and the other leg on the course line. Using the parallel ruler we transfer the 0900 LOP to the blue mark. As we notice, the two LOPs intercept at the point RF. This is our Running Fix position.

Doubling the angle

Another method of taking a running fix is by doubling the angle on the bow, having in mind the properties of an isosceles triangle. This fix requires the first bearing to be less than 45° from the bow. Assuming the course is 090° degrees and the speed is 10 knots, or 10 nautical miles per hour. We take a bearing of 060° degrees of the Charley radio tower at 0900 or 30° degrees from the bow. Now convert the compass bearings to true bearings and plot it on the chart. We observe the Charley radio tower, and when the new bearing reads 030° degrees, or 60° degrees from the bow, we note the time, 0915. Now convert the compass bearings to true bearings and plot it on the chart. Knowing the speed - 10 knots - and the elapsed time between the two bearings - 15 minutes - we use the formula: D is equal to S times T divided by 60, to calculate the sailing distance between the two bearings. In our case that is 2.5 nautical miles per hour. As we can see, the two bearings and the course form an isosceles triangle - ABC - where sides c and b are equal. That means that the distance from the Charley radio tower, when we took the second bearing at 0915 was 2.5 nautical miles. Using this method we have a bearing and a distance using only one object.

45-90

In the previous lesson we used "running fix by doubling the angle on the bow". Another method of plotting a running fix is the 45/90 method. The difference in the 45/90 method is that the angles used are specifically 45° and 90° from the bow.And together with the course line form an isosceles triangle - ABC - where the two sides c and b are equal.Using this method we have a bearing and a distance using only one object.

Introduction 1

In this lesson you will learn various methods used to determine your ship’s position, known as a Fix. A fix is the ship’s position or location on earth at a given point in time. We can determine a fix by intersecting two or more Line of Positions (LOPs), either straight or curved, simultaneously. A Fix can be obtained by using any of the following methods: By combining cross compass bearings, by combining a bearing and a visual range, or by combining a bearing and a contour line. A fix can also be obtained by combining two or more distances, combining a distance and a visual range, by combining a light house bearing and range, considering the rising or falling of the light on the horizon, or by combining a bearing and a vertical distance of a light house.

Introduction 2

A Fix can also be determined by using the Radar, the GPS, the Echo Sounder, and Loran. Traditionally, a fix can be established using Celestial Bodies.

Comb cross compass bearings 1

Combining Cross Compass Bearings A Fix can be obtained by combining Cross Compass Bearings using a hand-held compass. Assume your course is 360 degrees (North) and your speed is 7 knots. You are sailing near the coast and you have lighthouse A, lighthouse B and the island C in sight. The time is now 1015 and your last estimated position was at 0930. Checking your nautical chart, you locate and identify the two lighthouses and the island. Next, take compass bearings of the three identified objects, A, B, and C, with your hand held compass. Now, convert the Compass Bearings to True Bearings by applying the correction for Variation, using the formula “From Magnetic to True, subtract the Westerly Variation and add the Easterly Variation”. Let's assume that after applying the correction, the true bearing of the lighthouse A is 045°, the true bearing of the lighthouse B is 090°, and the true bearing of the island C is 135°.

Comb cross compass bearings 2

Now plot the bearings one by one on the Nautical chart. First the bearing from -lighthouse A: Place the parallel ruler to the compass rose at the 045° degree line and transfer that line, passing from lighthouse A and crossing the course line. Then, the bearing from lighthouse B: Place the parallel ruler to the compass rose on the 090° degree line and transfer that line passing from lighthouse B and crossing the course line. Third, the bearing from Island C: Place the parallel ruler to the compass rose on the 135° degree line and transfer that line passing from Island C and crossing the course line. Generally, when using three LOPs and due to small errors in the bearings, a triangle may form where they intercept. In this case the center of the triangle will be the fix position.

Compass bearing and visual range

A Fix can also be obtained by combining a compass bearing and a visual range. Assume your course is 360° degrees, or North, and your speed is 7 knots. While looking at the nautical chart you spot the lighthouse A and the range marks B and C. While waiting for the two range marks B and C to come visually in line, go to the nautical chart and connect them with a line, draw the first LOP, crossing the course line. Observe the two range marks, and as soon as they are in line, write down the time, let’s say 0930 hours, and immediately take a bearing on lighthouse A using the hand held compass. let's assume that after applying the variation correction the lighthouse bearing is 045° degrees true bearing. Place the parallel ruler to the compass rose at the 045° degree line and transfer that line passing from lighthouse A and crossing the course line. As you can now see, the lighthouse bearing crosses the pre-drawn LOP of the range marks. This point of crossing represents your fix position at 0930 hours.

Compass bearing and contour line

A Fix can also be obtained by combining a compass bearing and a contour line. This method is especially useful when approaching a harbor or an anchorage. Let’s assume you approach a harbor and your echo sounder is in good working condition and in operation. Checking the nautical chart, you spot the lighthouse A and the contour lines of 20 meters. As you approach for berthing, let’s assume that your echo sounder shows a depth of 25 meters (taking into account the boat’s depth and the tide, if any), and the depth is decreasing as you approach the 20 meter contour line. As soon as the echo sounder shows a depth of 20 meters (taking into account your depth and the tide if any), note the time - for example 0930 hours - and immediately take a compass bearing on lighthouse A with the hand held compass. Let's assume after applying the correction for the variation that the bearing is 321° true. Place the parallel ruler on the 321° degree line of the compass rose and transfer it so it passes from lighthouse A and crosses the 20 meter contour line. Draw this line. The point where the lighthouse bearing crosses the 20-meter contour line is the boat’s fix position at 0930 hours. Using the same method you can plot a fix position as you cross the 10 meter and 5-meter contour lines.

Distances and compass bearings 1

You can obtain a fix by combining two or more distances or distances and compass bearings. This is how you plot a fix position combining two or more distances: Let's assume you sail near the coast. The radar is in good working condition and in operation. Taking into account your last position, and after comparing the nautical chart’s coast line with that on the radar screen, you spot two points on the screen, A and B, from where you can take distances. The equivalent ones on the nautical chart are points A and B. Using the radar’s range marker you measure a distance of 5.2 nautical miles from point A, and 2.8 nautical miles from point B. You note the time - let’s assume it is 0930 hours. Then return to the nautical chart, and using the divider, span a distance of 5.2 nautical miles on the latitude scale which is closest to the present position and which runs along the sides of the chart. Apply this span, placing one leg of the divider at point A, and draw a semicircle near the course line. Now span a distance of 2.8 nautical miles and apply this span, placing one leg of the divider at point B, and draw a second semicircle intersecting the first semicircle and near the course line. The point where the two semicircles intersect is the fix position at 0930 hours.

Distances and compass bearings 2

This is how you plot a fix position combining distances and compass bearings: Using the radar’s range marker you obtain a distance of 5.2 nautical miles from point A and 2.8 nautical miles from point B. Immediately afterward, using the hand held compass, take a bearing of lighthouse B. Let’s assume that after applying the correction for the variation that the bearing of lighthouse B is 100° true. Using the divider you plot the two distances 5.2 and 2.8 nautical miles taken from point A and point B respectively, to the nautical chart. Then place the parallel ruler to the compass rose on the 100° degree line, and transfer that line passing from lighthouse B and crossing the course line. As you can see, the two distances and the compass bearing intersect. The point of intersection will be the fix position at 0930 hours.

Bearing and vertical sextant angle 1

A Fix can also be obtained by combining a compass bearing and a distance of the same lighthouse. You can determine the distance knowing the height and the vertical sextant angle of the lighthouse. Let’s assume you sail near the coast and, looking on your nautical chart, you spot the lighthouse A. Among the characteristics of the lighthouse, you read that it has a charted height of 103 meters or 338 feet. This is the height above mean high water spring tide. After calculating the height of tide at that time, the corrected height of the lighthouse is 105 meters or 345 feet. Use the sextant and measure the vertical angle of the lighthouse. Let’s assume, after applying the index error, that the vertical angle is 2 degrees and 30 minutes. Knowing the corrected height and the corrected vertical sextant angle of the lighthouse, calculate the distance, using the formula: D is equal to h times 0.565, divided by v, where D is the Distance in nautical miles, h is the Height of the Lighthouse in feet, and v is the Vertical sextant angle in minutes. In our case, 345 feet times 0.565 divided by 150 equals 1.3 nautical miles.

Bearing and vertical sextant angle 2

As soon as you have measured the distance to the lighthouse, in our case 1.3 nautical miles, note the time. Let’s assume it is 1000 hours. Immediately, take a bearing using the hand held compass. Lets assume that after applying the correction for the variation, the bearing is 045° degrees true. Now, to plot the fix position on the nautical chart, first use the divider, and span a distance of 1.3 nautical miles on the latitude scale that is closest to the course line, and runs along the sides of the chart. Apply this span, placing one leg of the divider at point A, and draw a semi-circle near the course line. Second, place the parallel ruler to the compass rose on the 045° degree line and transfer that line passing from lighthouse A, crossing the course line. The point where the semicircle and the compass bearing intersect is the fix position at 1000 hours.

Steps to be taken

Here we will see how you can obtain a position line or a fix at night, using a light rising or dipping on the horizon. Let s assume you approach a charted light at night. - When you first see the light take a bearing on it with the handheld compass - for example 045° degrees. - Next, note the time. 2200 hrs. - Third, note the height of eye of the observer above sea level. 5 feet (or 1.52 meters) and - finally, note the height of the light house allowing for the height of tide. 140 feet or 42.67 meters. The height of a light above chart datum can be found in the chart or in the list of lights or other publications. To calculate the distance off the light use either: - the almanac s distance of sea horizon in nautical miles table, or - the formula 2.08 x (" light elevation + " eye height).

Using tables-formula-plotting

• Using the almanac s table, enter with the height of eye and find the distance A. For example, for 5 feet the distance A is 2.57 nm. Then enter with the height of a light and find the distance B. For example, for 150 feet the distance B is 13.61 nm. The sum of distances A and B is 16.18 nm. - Use the formula distance from the light = 2.08 x (" light elevation + " eye height) where the heights are calculated in meters. Using 42.67 meters for the value of the light elevation and 1.52 meters for the value of the eye height, we add the two and then multiply by 2.08. We find the distance from the light is: 16.15 nm. - The next step is to plot the bearing 045° degrees of the light on the chart after converting it to true bearing. Using the divider, span a distance of 16.15 nm on the latitude scale. Apply this span by placing one leg of the divider at the light on the nautical chart and drawing an arc cutting through the plotted bearing at the point F. this is a fix position at 2200 hours. Follow the same procedure using a light dipping on the horizon, that is, the moment the light vanishes from the horizon.

Navigation In restricted visibility

Introduction

The primary cause of restricted visibility is fog, heavy rain, very rough seas, haze or snow can also cause visibility to be restricted. Sailing in restricted visibility presents hazards, such as collision with another vessel or object, and navigational errors, such as setting off course and running aground. Fog is quite difficult to predict and is likely to take you by surprise. Still, there are some warning signs that can help you to predict fog is coming

Precautions 1

The first thing to do when you notice approaching fog is to plot an accurate fix on the chart as soon as possible. If for any reason you cannot get an accurate fix, then rely on your Dead Reckoning or Estimated Position. Start sounding your foghorn. Sailing vessels must sound one prolonged blast plus two short blasts every two minutes. Turn on your navigation lights. Rig up the radar reflector as high as possible if one is not permanently fitted. Remember, the big ships are more likely to maintain their speed, relying on their radar to detect other ships. If the sea is rough, they probably won’t detect you, since the echoes from the waves cover the small echo from your sailing boat. Make sure that all crew wear their life jackets and that the life raft is clear and ready to use. In addition, have some red and white flares handy.

Precautions 2

Other steps to be taken in restricted visibility are: Post a lookout for lights and signals of other vessels well forward, away from the noise of the engine. If the boat is fitted with radar, turn it on as soon as the visibility is reduced, and place a crew member with radar experience to monitor it. If the engine is not running, then start and warm it up to ensure that it will start instantly in case of emergency. If you have a GPS use the data and plot an accurate fix on the chart. However, always check this data against other sources, such as radar, Loran or depth recorder. You may have to reduce your speed, but always keep steerageway on your boat.

Strategy and limitations 1

If you are in a busy shipping lane, mark you exact position, if possible, on the chart, note the positions and courses of other vessels. Alter your course immediately to get clear of the lane and other ships as soon as you can, sailing to more shallow waters. Use your engine if necessary. When you navigate near the coast, pay attention to the sound signals emitted from the buoys and lighthouses. The type of signals they emit is marked on the chart, or you can find them in the relevant pilot books. When you are using the engine during fog, shut it down at regular intervals and listen for sound signals, either from vessels or buoys and lighthouses.

Strategy and limitations 2

When you are navigating near the coast or in a channel where the visibility is restricted, consult the depth recorder, and try to follow a depth contour on the chart that provides navigable waters and is clear of charted hazards. Approaching a harbor in restricted visibility, use your depth recorder and make a note of the depth contours as you cross them. That will provide you with a position line. Additionally, locate a buoy on the chart and sail close to it, following the nearest depth contour.

Sound signals 1

Here are the sound signal rules to be followed by vessels in restricted visibility: A power-driven vessel underway must sound one prolonged blast every two minutes. A power-driven vessel underway but stopped and making no way through the water must sound two prolonged blasts every 2 minutes with an interval of about 2 seconds between them. A vessel not under command

Sound signals 2

A vessel at anchor may in addition to the bell and/or gong, sound one short, one prolonged and one short blast to give warning of her position, and of the possibility of collision, to an approaching vessel. A vessel aground must ring the bell, and if required, sound the gong, and in addition, must ring three separate and distinct strokes on the bell immediately before and after the rapid ringing of the bell. A vessel of less than 12 meters in length is not obliged to give the previously described signals, but if she does not, shall make some other efficient sound signal at intervals of not more than 2 minutes. A pilot vessel when engaged on pilotage duty shall, in addition to the signals prescribed for power-driven vessels, sound an identity signal consisting of four short blasts.

Test

This is an interaction - have fun!

Causes of tides

Causes of tides 1

Tides are the vertical rise and fall of the surface of a body of water, caused primarily by the gravitational attraction of the moon and to a lesser extent, the sun. The rotation of the earth is the primary cause of two high tides and two low tides per day, also called semidiurnal tide, experienced in most parts of the world. Some locations on earth have only one high tide and one low tide per day - called diurnal tide - due to the path of the moon and other geographical factors. A few other places experience a combination of diurnal and semidiurnal tides, called mixed tides. The difference in height between a high tide going to a low tide, or a low tide going to a high tide is called the tidal range. The rising tide is called the flood tide and the falling tide is called the ebb tide.

Causes of tides 2

Spring tides are those with higher high tides and lower low tides than normal, or a greater range of tide. They occur when the sun and the new moon, or the sun and the full moon are in straight line with the earth exerting a larger than normal gravitational force, and therefore causing a greater than usual tidal range. Neap tides are tides with lower high tides and higher low tides than normal - in other words - a smaller range of tide. These occur when the moon is in a quarter phase and the sun, moon and earth form a right triangle. Because the sun is not in a straight line with the earth, the gravitational pull of the sun counteracts the gravitational pull of the moon and as a result, the tidal range is unusually small.

Tide heights and chart datum

Tide heights chart datum 1

Let’s have a closer look at "Tidal Heights" and "Chart Datum". On nautical charts, soundings and drying heights are measured from Chart Datum. Chart Datum is the Lowest Astronomical Tide or L A T , meaning the lowest level to which the tide is expected to fall. All depths on a chart are measured below chart datum and all drying heights are measured above it. Non-drying heights, for example a lighthouse, are always measured above Mean High Water Springs, not Chart Datum, as an added safety margin. The height of tide is always measured above Chart Datum.

Tide heights chart datum 2

The difference of height between Mean High Water Spring (MHWS) and Mean Low Water Spring (MLWS) is referred to as spring range. Also, the difference in height between Mean High Water Neap and Mean Low Water Neap is referred to as neap range.

Rule of twelfths

Rule of twelfths 1

There are two methods of calculating the tidal height. The first uses the tide tables, which is a very accurate method, and the second uses the "Rule of Twelfths", which is not so accurate and should be used with caution! To use the "Rule of Twelfths," we assume that the tide rises and falls in the same pattern. A six-hour tide is expected to rise or fall in the 1st hour 1/12 of its range. In the 2nd hour 2/12 of its range. In the 3rd and the 4th 3/12 of its range. In the fifth hour 2/12 of its range and in the 6th hour 1/12 of its range.

Rule of twelfths 2

To find the times, heights and range of the tide it is necessary to consult the tide tables. Let’s use the "Rule of Twelfths" for the port of Portsmouth on the 1st of November. The first high water is at 00:45 UTC and the height of tide is 4.0 meters. The next low water will be at 05:52 with a height of tide of 0.5 meters. Now we calculate the range by subtracting the high water from the low water. In our case 4.0 meters minus 0.5 meters equals 3.5 meters. Dividing the range by 12 gives us a unit for our calculation - 3.5 meters divided by 12 equals 0.33 meters.

Rule of twelfths 3

To calculate the fall of the tide for 02:45 UTC we now use the "Rule of Twelfths". First we have to calculate the time. 02:45 UTC minus 00:45 UTC gives us 2 hours. As we already know, in the first hour the tide will fall 1/12 of its range, which is 0.33 meters. For the second hour the tide will fall 2/12 of its range, which is 0.66 meters. The total fall for the tide in two hours is 0.33 plus 0.66 meters, which equals 0.99 meters. Now we can calculate the height of the tide for 02:45 UTC. Height of the tide for 02:45 UTC is 4.0 meters minus the fall of the tide - 0.99 meters - equaling 3.01 meters. The final step is to add the height of the tide to the charted depth on the chart.

Tides for a standard port

Tides for standard port 1

Let’s now use the tide table to calculate the tide for a standard port. But first, what is a standard port? In the tide table we distinguish between standard ports and secondary ports. A standard port is a port for which the times and heights of high and low water are predicted for every day of the year. A secondary port is a port that has an assigned standard port. The reason for the use of secondary ports is that it is impossible to list the times of high and low of each port in the world. The tidal curves of the secondary port and the assigned standard port are assumed to be the same.

Tides for standard port 2

Here is an excerpt of a Tide Table. In the first line you see the name of the standard port and where it is located. In the second line information is provided about the time zone in which the times of high and low water are calculated and the coordinates of Portsmouth. In the third line you find the month and the year from which times and tides are calculated. On the left side the day of the month. On the right side you will find times and heights of the tide.

Tides for standard port 3

Let’s now find out the times and heights of high and low water on September 1st. Note that all times are in UTC (Coordinated Universal Time), formerly known as GMT (Greenwich Mean Time). Watch out - if you are on British Summer Time, you have to add one hour to UTC. On September 1st high water is at 09:56 and 21:30, and low water is at 02:50 and 14:30. Now, if you want to know the actual depth of water in Portsmouth at 14:30, you just have to add the charted depth of Portsmouth and the low water. Low water at 14:30 is 0.4 meters and the charted depth is 6 meters. We add 0.4 meters and 6.0 meters, so the actual depth in the harbor of Portsmouth is 6.4 meters. In case the height of low water is minus, you have to subtract instead of add.

The tidal curve

The tidal curve 1

The Tidal Curve is another method of determining times of high and low water. Before you use the curve, note the times and heights of tide for the day from the tide table. Let’s again use Portsmouth on September 1st. First you have to enter the time of the day nearest high water - if it is now 09:45 then we take the next high water at 9:56. Now we mark the low water on the lower scale and the high water on the upper scale, and connect both values with a straight line.

The tidal curve 2

If you need the height of the tide for a particular time, for example for 13:00, just enter the required time at the timescale grid. 13:00 is roughly 3 hours after high tide. Then check whether the tidal range is close to a spring range or neap range. In our case we have a tidal range of 3.8 meters; 4.2 - 0.4 equals 3.8 meters. As we can see from the mean ranges, 3.8 meters is close to a spring range. Next we draw a line from 3 hours after high water to the spring curve. Here we can interpolate by eye. From the intersection of the line and the spring curve we draw a horizontal line to the high and low water line. From here we draw a line to join the top scale. The number at this point is the height above chart datum of the tide at the required time. To calculate the total depth of water in the Port of Portsmouth, we add the height of tide to the depth shown on the chart.

Corrections for a secondary port

Corrections for secondary port 1

Now let’s see how we calculate the times of high and low water in a secondary port. Let’s take Barfleur. First we have to look up which standard port is assigned to Barfleur, and we find it is Cherbourg. For Barfleur we want to obtain the time of high water in the evening. So first we look up the time of high water in Cherbourg. As we can see from the table, high water is at 18:46 and the height of the tide is 5.6 meters. We make a note of these figures.

Corrections for secondary port 2

Now we take the table for the secondary port, Barfleur. At the top we have the times of high and low water, and the time differences. To the right we have the heights of high and low water, and the height differences. Let’s first calculate the time difference. 18:46 lies a little over half the interval between 15:00 and 21:00. Now we have to interpolate between 51 minutes and 44 minutes. The time difference for high water should then read 47 minutes. Then we add the minutes to 18:46 to equal 19:33. The high water in Barfleur will be at 19:33.

Corrections for secondary port 3

We calculate the height of the tide in the same manner. 5.6 meters lies at about half the interval between plus 0.3 and plus 0.9 meters. So the height difference for high water should read plus 0.6 meters. We apply this figure to the high water in Cherbourg. 5.6 meters plus 0.6 meters equals 6.2 meters. The high water in Barfleur at 19:33 will be 6.2 meters.

General

General 1

Aids to navigation include lighthouses, beacons, buoys, towers, floating aids and permanent structures. These are all man-made devices that can be used to warn of a danger, to mark a location, or to indicate a safe route. Aids to navigation are placed along coasts, navigable and non-navigable waters in order to assist the Navigator to determine his or her position in relation to land and hidden hazards. By day we can identify an aid to Navigation by location, shape, color scheme, auxiliary features (sound signals, racon), and markings, such as name and number. By night we can identify an aid to Navigation by it’s light. Each light has three distinctive characteristics: the color, the period and the phase characteristic.

Lighthouses and Beacons

A Lighthouse is a major structure equipped with a light on top, with particular characteristics of the light that vary from lighthouse to lighthouse. The structure has distinctive color, shape and specified height . Many lighthouses are quipped with sound signals very useful in restricted visibility. They are established to assist the navigator and are used for landfalls, coastal passages and key navigational points. A beacon is a pile structure, rigidly attached to the bottom or to the shore, with a light installed. A beacon has a distinguishing shape and color. It has a letter or number, and usually a reflective tape around it. If a beacon is unlighted, it is a day beacon. A beacon marks navigational hazards, usually in shallow bays, small harbors or inland waterways, and indicates a channel.

Bouys

Buoys are floating aids to navigation. They may have the shape of a cone, can, pillar, spar or sphere, have numbers or letters or both. They have a distinguishing color, and a top mark if any, and they also have a characteristic light. They may be equipped with a distinctive sound signal, for example, a whistle, gong or bell. A buoy is usually equipped with a radar reflector that enhances the echo on a radar screen. It can also be equipped with a "RACON" that allows the buoy to emit an identifying specific and independent radar signal.

Bouyage Systems 1

There are two major types of buoyage systems: the lateral system and the cardinal. In the Lateral system the buoys indicate the port and starboard boundaries of a route to be followed e.g. a channel. The Lateral system differs between buoyage system A and B. Buoyage system A is employed in Europe, Africa and Asia, where the green buoys mark the starboard side of the channel when approaching from seaward, while buoyage system B is used in North, Central and South America, Korea and the Philippines, where the red buoys mark the starboard side of the channel when approaching from seaward. In the Cardinal system, the buoys indicate where the mariner may find navigable water, and are used in conjunction with a compass.

Bouyage Systems 2

Other Buoys are sometimes used to indicate isolated dangers having navigable water around them, and are known as Isolated Danger marks. They are also used to indicate the location of navigable water surrounding their position, e.g. middle channel, and they are known as Safe Water marks. And they can be used to indicate special features e.g. spoil grounds or prohibited anchorages.These are known as Special marks. Do not rely entirely on any floating navigational aid. It could have been displaced or damaged by heavy weather, it could have been re-numbered or changed, or may have been removed for repairs and not replaced. Always double check your position using Radar, GPS, and by taking bearings.

Lighted navigation aids

Basic characteristics - Color

To use a light as an aid to navigation, you first have to see it and secondly you have to identify it. In the nautical chart it is symbolized by a purple exclamation point and/or by a purple circle. The basic identification characteristics are the color of the light, the period and the phase characteristic. The color of the light can be white, green, red or yellow. If the color is green the abbreviation "G" is printed near the symbol

Period of Light

The period of a light is given in seconds and is timed from the first flash of a circle until the first flash of the next circle. For example, on the nautical chart we see a lighted navigation aid, and written near the purple exclamation point is Gr. Fl.(4) 15s - group flashing, four flashes, every 15 seconds. This means that the light starts flashing for four flashes, followed by a period of darkness, then starts the four flashes again, followed by a period of darkness and so on. Using a stop watch and timing a cycle from when the first of the four flashes appears, including the period of darkness, until the first of the four flashes appears again, we find that the period of that light is 15 seconds.

Light Phase 1

The Light phase is the sequence or pattern of the light shown, within one complete circle or period. We have the following common patterns: Fixed (F.): this light shines with a steady and unblinking intensity Flashing (Fl.): the duration of darkness is always greater than the duration of the light, and appears as a single flash at regular intervals. The flashes occur not more frequently than 30 times per minute. For example Fl. 10s Quick Flashing (Qk.Fl.): the duration of darkness is always greater than the duration of the light, and the flashes in this pattern are at least 60 times per minute. For example Qk.Fl 20s. Very Quick Flashing (V.Qk.Fl.): here again the duration of darkness is greater than the duration of the light, and the flashes are at least 100 times per minute. Interrupted Quick Flashing (I.Qk.Fl.): in this pattern we have at least six quick flashes followed by a period of darkness (standard period of ten seconds) in one period.

Review Light Phase 1

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Light Phase 2

Isophase (Iso.): the duration of darkness is equal to the duration of the light at any length period. Group flashing (Gp.Fl.): in this period there is a combination of two or more groups of flashes in one period at regular intervals. For example (Gp.Fl. 3+5). Occulting (Occ.): the duration of the light is always greater than the duration of darkness and appears at regular intervals. Morse (Mo.(A)): in this pattern the light shows one short flash followed by a long one which is equivalent to the letter "A" in Morse code. Alternating (Al.): this pattern is used for special applications where great caution is required. In this case the light alternates color, for example Al.W.R.. Long flashing (L.Fl.): in this pattern the light shows a long flash - at least 2 seconds in each period.

Review Light Phase 2

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Light categories

The lights used as aids to navigation are divided into two main categories: the major lights and the minor lights. The major lights are subdivided into two groups: the primary major lights and the secondary major lights. The primary major lights are of very high intensity, long range, and used for landfalls, coastal passages and key navigational points. They are placed in lighthouses, lightships and light towers. The secondary major lights are of high intensity, of shorter range, and they are placed in harbors, and river entrances, and along seacoasts. The minor lights are of low to moderate intensity, placed within harbors, along channels and rivers and are often used to mark isolated dangers.

Types 1

There are 3 types of lights used as aids to navigation: Alternating lights, Sector lights, and Range lights. Alternating lights are used when great caution is required, for example when entering a harbor. The light alternates color, for example Al.WR.. Sector lights are used to point out hazards to navigation and to warn the navigator as he is approaching the light from this specific sector. The sector could be either a few degrees in width, marking a navigation hazard such as a shoal or a rock, or could be a sector which covers a wide range, marking a safe approach in deep water. True bearings are used to form the limits of the various sectors, observed from a vessel that moves in a clockwise direction around the light.

Types 2

Range lights are used to indicate a safe passage inside channels, and recommend a course where navigational hazards are present on both sides. Usually they come in pairs and are situated in such a way that one shows over the other when they are in line. The light close to the observer is called the front light and the light behind is called the rear light. For example, to navigate safely in a channel with range lights, the front light must be in line with the rear one. If they are not in line and the front light is on the right side, then you are off course and on the port side of the line. If the front light is on the left side, then you are off course and on the starboard side of the line. During daylight a range consists of a pair of beacons, and lining up those beacons is similar to lining up the lights.

Light ranges

Nominal Range - Luminous Range

The nominal range of a light is the maximum distance at which a light can be seen when the visibility is 10 nautical miles. The light’s nominal range can be found in the Light List. The luminous range of a light is the maximum range at which an observer can see a light under existing visibility conditions. Luminous range does not take into consideration the elevation of the light, nor the observer’s elevation. The luminous range can be determined by knowing the nominal range of the light and the existing visibility. Roll over the ranges to review.

Calculating the Luminous Range

Calculating the Luminous range of a light. Let's say the nominal range of light "X", extracted from the Light List, is 20 nautical miles, and the existing visibility is 11 nautical miles. What we want to find out here is the luminous range. Entering the luminous range diagram, we locate the nominal range of 20 nautical miles on the bottom horizontal line. From there we draw a vertical line upward until it intersects the curve representing the existing visibility of 11 nautical miles. From this point we draw a horizontal line to the right, intersecting the vertical luminous range scale at 21 nautical miles. Therefore the Luminous range of this light "X" is 21 nautical miles.

Geographic Range - Computed Range

The Geographic range of a light is the maximum distance at which a light can be seen when the observer’s elevation is at sea level. The Computed range of a light is the maximum distance at which a light can be seen, taking into consideration the height of both the light and the observer. The distance at which a light can be seen increases as the elevation of the light and the observer’s height increase. To calculate the Computed range of the light "x", you need to first know the elevation of the light, which can be obtained either from the Light List or the nautical chart. You must also know the observer’s elevation above sea level.

Calculating the Computed Range

Calculating the Computed range of the light "X". Let's say that light "X" has an elevation of 170 feet above the water and the observer’s elevation is 8 feet. Using the light’s elevation, we calculate the light’s Geographic range using the formula: 1.17 times the square root of the height = distance to the horizon in nautical miles. In our case 1.17 times 13.04 equals 15.25 nautical miles. This is the Geographic range. Secondly, knowing the observer’s elevation we calculate the observer’s Horizontal distance using the same formula. In our case 1.17 times 2.83 equals 3.31 nautical miles. This is the observer’s Horizontal distance. By adding the two values, 15.25 and 3.31 nautical miles, we determine the Computed range of the light "X". In our case 18.56 nautical miles. By comparing the Luminous range of the light "X", 21 nautical miles, and the Computed range, 18.56 nautical miles, we can determine the maximum range at which the light "x" may be seen. In our case this is 18.56 nautical miles.

Lists and corrections

Lists and Corrections

To become acquainted with the latest significant changes to lights and fog signals, e.g. light vessels, light structures, light buoys, etc., you have to consult the List of Lights and Fog Signals or the Yachtsman’s Almanac. These publications provide you with detailed changes. Since up to 17 months may elapse between publications, Notices to Mariners should be consulted for up-to-date information. These Notices supply you in the meantime with any changes that may have occurred. Notices to Mariners also provide you with other recent information such as chart corrections, navigational warnings etc.

Buoyage System

Lateral Marks

Lateral marks: As stated, lateral marks indicate the port and starboard boundaries of a route to be followed e.g. channel. Lateral marks differ between buoyage system A and buoyage system B. Lateral marks are usually positioned to indicate port and starboard boundaries in well-established channels. When entering a port, the green mark (the starboard hand buoy) should be seen on your vessel’s starboard side, and the red mark (the port hand buoy) should be seen on your vessel’s port side. When you are departing the port, the green mark should be seen on your vessel’s port side, and the red mark should be seen on your vessel’s starboard side. The port hand mark has the shape of a can or a spar, and is colored red with a single red can as a top mark (if there is any). By night a port hand mark shows a blinking red light. The starboard hand mark has the shape of a conical or a spar, and is colored green, with a single green cone point upwards as a top mark (if there is any). By night a starboard hand mark shows a blinking green light.

Cardinal marks Introduction

Cardinal marks indicate where the mariner may find navigable water. These marks are used in conjunction with a compass. Here we have four quadrants,: North, East, South, and West. The danger in the middle is the point of interest. From the point of interest we bound the north quadrant by the true bearings, NW-NE the east quadrant by the true bearings, NE-SE the south quadrant by the true bearings, SE-SW, and the west quadrant by the true bearings, SW-NW.

Cardinal Marks 1

Every Cardinal mark is named after the quadrant in which it is placed. Therefore, we have the North Cardinal mark, the East Cardinal mark, the South Cardinal mark, and the West Cardinal mark. The mariner is safe if he passes

Cardinal Marks 2

The East Cardinal mark has a shape of a pillar or spar, and is colored black with a yellow horizontal band in the middle. As a top mark it has two black cones, one above the other, base to base. The East Cardinal mark exhibits a white light with a rhythm of very quick flashing, (3 times every 5 seconds), or quick flashing (3 times every 10 seconds). The South Cardinal mark has a shape of a pillar or spar, and is colored yellow above black, as a top mark it has two black cones, one above the other, with the points downward. The South Cardinal mark, exhibits a white light with a rhythm of 6 very quick flashes plus a long flash every 10 seconds, or 6 quick flashes plus a long flash every 15 seconds. Each long flash lasts for at least two seconds.

Cardinal Marks 3

The West Cardinal mark has a shape of a pillar or spar, and is yellow with a black horizontal band in the middle. As a top mark it has two black cones, one above the other, point to point. The West Cardinal mark, exhibits a white light with a rhythm of 9 very quick flashes, every 10 seconds, or 9 quick flashes, every 15 seconds. To memorize the light rhythm of the cardinal marks: Associate the number of flashes of each group with that of a clock face. Three o’clock is east, six o’clock is south, and nine o’clock is west. To memorize the colors of the cardinal marks, associate the black color and the points of the double cone top mark. For example, in the north cardinal mark, the points of the cones showing upward, indicate that the black color is on the upper part of the buoy. In the south cardinal mark, the points of the cones showing downward indicate that the black color is on the down part of the buoy. The same is true for the East Cardinal mark and for the West Cardinal mark.

Isolated danger marks

An Isolated Danger mark indicates an isolated danger of limited extent, which has navigable water all around it. This danger might include rock, a wreck or an isolated shoal. An Isolated Danger mark has a shape of a pillar or spar, and is black with one or more broad horizontal red bands. As a top mark it has two black spheres, one above the other, clearly separated. The Isolated Danger mark exhibits a white light flashing in pairs. To memorize the light rhythm: Associate the group of two flashes with the two black spheres.

Safe water marks

The Safe Water mark indicates that there is navigable water all around the mark

Special marks

The Special Mark indicates a special area or feature, for example: Traffic separations, spoil grounds, cable or pipelines, to define a channel for deep draft vessels within a channel, or military exercise zones. The Special Mark may have a shape of any kind, and is yellow . As a top mark it has a single yellow "X" shape. The Special Mark, exhibits a yellow light, and has any rhythm other than those used for the white lights of cardinal, isolated danger and safe water marks, and that cannot be confused with any other light in the area.

New Danger

The term “New Danger” is used to describe newly discovered hazards not yet shown on nautical charts. These hazards include natural obstructions, such as sandbanks or rocks, or man-made dangers such as wrecks. The new danger will be marked according to the rules and should have an appropriate cardinal or lateral VQkFl (very quick flashing) or QkFl (quick flashing) light character. If the danger is very grave the mark will be duplicated. The duplicated mark is identical to its partner and may carry a racon coded “W” (Whiskey), with a signal length of 1 nautical mile on the radar screen. The duplicated mark will be removed when the new danger has been sufficiently promulgated.

Preferred channel marks

The preferred channel mark indicates where a channel divides when proceeding in the “conventional direction of buoyage”. The preferred channel mark to starboard has a shape of a can, pillar or spar, and is red with one green horizontal band. As a top mark, if any exists, it has a single red can. When fitted with a light, it exhibits a red light with a composite group flashing of 2 + 1. The preferred channel mark to port has a shape of a cone, pillar or spar, and is green with one red horizontal band. As a top mark, if any exists, it has a single green cone pointing upward. When fitted with a light, it exhibits a green light and has a composite group flashing of 2 + 1.

IALA marks Trainer

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How the weather works

Introduction

An air mass is a huge dome of air whose temperature and humidity characteristics remain fairly constant over a horizontal distance. This horizontal distance can extend up to hundreds or thousands of kilometers. Air masses are classified according to the characteristics of their source regions. A source region is the area where an air mass originated. The characteristics of an air mass, such as temperature and moisture content, are acquired from the source region.

Temperature and moisture characteristics

As we have learned, air masses are classified according to their source regions. Source regions may have one of four temperature attributes: equatorial, tropical, polar or arctic. In terms of moisture characteristics they can be either continental or maritime. On a weather map moisture characteristics are abbreviated “c” for continental or “m” for maritime

Classification of weather fronts

When two air masses with different temperature meet, they normally develop a sharp boundary between them. The boundary area where the temperature difference becomes intensified is called a front. The classification of weather fronts are as follows: Cold Front, Warm Front, Occluded Front and Stationary Front.

Introduction

Clouds are often very important indicators of imminent weather changes. When they are observed at various times and regular intervals, even an approaching mid-latitude storm can be recognized. In an approaching storm, a change of cloud structure and type will take place. First, high cirrus clouds appear, followed by high-level cirrostratus clouds and low thick altostratus clouds. When the storm is finally close at hand, dark clouds will bring high winds and pouring rainfalls. But how do clouds form? Clouds are nothing more than water vapor that condenses on microscopic airborne particles, like dust and sea salt, which then accretes into a visible form.

How clouds are formed

The cloud formations of interest to the mariner are formed in the Troposphere. The Troposphere is a layer of the earth’s atmosphere that extends from the earth’s surface to about 24.000 feet (7.300 meters) above the poles, and to about 65.000 feet ( 19.800 meters) above the equator. Clouds in the Troposphere are made up of water droplets or ice crystals, and can occasionally be a combination of both. The consistency of clouds always depends on the temperature.

Classification

Clouds are classified by their general appearance and level. Cloud names are Cirrus, Stratus and Cumulus. To indicate the level of a cloud, a prefix is given to the cloud name, like Cirro and Alto. Cirro indicates high clouds with bases above 20.000 feet. Alto indicates mid-level clouds between 7.000 and 20.000 feet. There is no prefix for low clouds. Low clouds are found from near the ground to about 7.000 feet. Often you can find the word “Nimbo” added to the beginning or “Nimbus” added to the end of a cloud name. This means that the cloud is producing precipitation.

High clouds

High clouds are Cirrus, Cirrostratus and Cirrocumulus. Cirrus clouds are thin wispy clouds, composed predominantly of ice crystals. Thick patches of Cirrus clouds indicate that showers are nearby. Cirrus clouds that are shaped like commas indicate that a warm weather front is coming. Cirrostratus clouds are transparent and show little or no structure. When Cirrostratus clouds are increasing and are in a continuous sheet, a warm or occluded weather front will approach, bringing rainy, stormy conditions. You can expect good weather at your location when Cirrostratus clouds are not increasing. Cirrocumulus are white and grainy with no shadowing clouds. Depending on the location, these clouds can foretell bad or good weather. In the British Isles they usually indicate good weather, but in Southern Europe they can indicate bad weather.

Mid-level clouds

Mid-level clouds are Altostratus and Altocumulus. Altostratus clouds are usually grayish clouds that cover part or all of the sky. These clouds are composed of water droplets or ice crystals. At sea, Altostratus clouds are an important weather indicator. These clouds can indicate that rain or snow is approaching, associated with poor visibility and huge waves with heavy swell. Altocumulus clouds are a detailed cloud deck of cumuliform clouds. These clouds are composed mainly of water droplets. Ice crystals are only present at very low temperature. When altocumulus clouds are in parallel bands, a warm front with continuous rain or snow can be expected. Altocumulus clouds rising from their flat base indicate heavy showers and thunderstorms.

Low clouds 1

Low clouds are Nimbostratus, Stratus, Stratocumulus, Cumulus and Cumulonimbus. Nimbostratus clouds are dark and quite homogeneous clouds. These clouds are associated with heavy downpours, high winds and sea conditions that are hazardous for small vessels. Take precautions when Nimbostratus clouds are in sight. Stratus clouds are gray, thin and usually featureless. These clouds bring fine drizzle or snow grains, and in certain conditions, fog. Stratocumulus clouds can cover part or all of the sky. Sometimes some holes in the cloud deck can be observed. These clouds usually produce light rain or snow. Stratocumulus clouds that have been formed from degenerating cumulus clouds usually indicate fair weather. Visibility may be reduced when precipitation occurs.

Low clouds 2

Cumulus clouds are cauliflower-like clouds whose contours change constantly. Cumulus clouds can have slight or extensive height. With little vertical growth, these clouds indicate fair weather. With a large vertical extent, these clouds are associated with heavy showers and gusty winds. Cumulonimbus clouds are heavy dense storm clouds with large vertical extent - up to 13 miles. These clouds are also called thunderheads, and bring heavy rain, lightning and gusty surface winds. They should be avoided by all means. In certain conditions tornadoes or water spouts can be expected.

Warm front

A warm front occurs when warmer air glides over colder air. This happens because warm air is generally lighter than colder air. As warm air rises, it cools and becomes saturated with moisture. Clouds form when the moisture in the warm air condenses. Warm fronts are often accompanied by low nimbostratus clouds with rain or drizzle. Because of the rain, the colder air may become saturated and cooled, often resulting in fog formation. If the warm air is stable, altostratus and cirrostratus cloud forms. Conversely if the warm air is unstable, cumulonimbus and altocumulus cloud forms. The latter clouds produce severe thunderstorms.

Cold front

Let’s look at the various types of fronts. A cold front occurs when a cold air mass replaces a warm air mass. Because the cold air is denser and heavier than warmer air, the wedge of cold air pushes under the warm air, lifting it up. The warm air can be in a stable or unstable condition. Within a stable air mass, there is static stability in the lower layers, very little convection and a low degree of turbulence. In an unstable air mass, static instability prevails, along with greater convection and high turbulence. If the warm air is stable, overcast and rain occur ahead of the front. If the air is unstable, cloud will form, typically cumulus and cumulonimbus accompanied by thunderstorms. Occasionally a continuous line of thunderstorms will form along the front, which is also called a squall line. Squalls may create fierce and destructive conditions such as strong winds, tornados, hail or sleet. Note: A cold front usually moves faster than a warm front. If it is associated with bad weather, you may have little time for safety preparations and course changes.

Occluded front

An occluded front occurs when a cold front catches a warm front. There are two types of occluded fronts: the-cold-occlusion front and the warm-occlusion-front. A cold occlusion occurs when the air mass behind the occluded front is colder than the air mass ahead of it. A warm occlusion occurs when the air mass behind the occluded front is warmer than the air mass ahead of it. A cold occluded front is normally more severe than a warm occluded front because the rainfall is heavier, and higher gusts can be expected during the passage of the front. Typically, precipitation occurs on both sides of cold and warm occluded fronts. Also, the cloud and weather sequences are a combination of characteristics of both cold and warm fronts.

Stationary front

A stationary front occurs when a warm or a cold front stops moving. As soon as a front resumes movement, it again becomes a cold or a warm front. When crossing from one stationary front to the other, a noticeable change in temperature and/or a shift in wind direction can be observed.

Introduction

The unequal heating of the earth between equator and poles causes meridional winds. Due to the rotation of the earth, winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This movement of great air masses is responsible for the general pattern of circulation of air parcels, but it also generates something else: whirling air masses of high pressure and low pressure cells called Highs and Lows.

Highs

Highs are also called anticyclones. In the Northern Hemisphere winds blow clockwise around an anticyclone, and in the Southern Hemisphere winds blow counterclockwise. The winds on the outer edges of a high blow stronger than they do towards the center. Highs usually move slowly and can remain stationary for weeks. Anticyclones bring characteristically good weather with light to moderate winds. Skies are mostly clear or have thin layers of cloud. Under certain conditions, anticyclones can also cause hazy weather or fog. When a high interacts with a low, strong winds and clear skies can be expected.

Lows

Lows are also called depressions. In the Northern Hemisphere, winds blow counterclockwise around a depression, and in the Southern Hemisphere winds blow clockwise. Winds blow stronger in the center of a low than they do on its outer edges. Depressions usually travel from east to west, and can vary greatly in size, velocity and strength. They bring characteristically unsettled weather, strong winds and heavy rainfall.

Introduction

Land has the ability to heat and cool far more quickly than the sea. The temperature between the land and the sea can be different at any point during day and night. This temperature discrepancy between land and sea can develop local winds, also recognized as sea and land breezes. As a general rule, we can say that the greater the difference in temperature between land and sea, the greater the wind.

Sea breeze

As we know, land masses heat up more quickly than sea masses, especially during the day. As the air heats up, the air parcels begin to rise and create low pressure areas at ground level. At a height of nearly 600 meters (2000 feet) the warm air increases speed toward the sea and replaces the cooler air, which replaces the rising warmer air. A circulation system has then developed - the so-called sea breeze. Sea breezes can occasionally reach more than 15 knots.

Land breeze

The converse of the sea breeze is the land breeze. At night the land mass cools more rapidly than the sea and the opposite circulation pattern takes place. The air over the land cools, sinks and raises the pressure. The air over the sea is warmer and continues to rise. In general, land breezes are lighter than sea breezes.

Introduction-dew point

Fog can be a dangerous weather phenomena. Fog may form either when there is a lot of moisture near the ground, or when the air near the ground is cooled to its dew point. But what is the dew point? Scientifically speaking, the dew point is the temperature to which an air parcel must be cooled, assuming that the pressure and water vapor content are constant, in order for saturation to occur. In simple terms, at the dew point the air contains as much moisture as it can hold. When the air near the ground cools to this temperature, water vapor from the air will become visible as dew on the ground or as fog in the air.

Expecting fog

When can you expect fog to occur? A simple rule is: when the difference between the air temperature and the dew point is large and does not decrease, no fog is expected. When the difference between the air temperature and the dew point is small and decreases, or the difference becomes even zero, you should watch out for fog. Let’s have a closer look at how you can calculate the dew point. In nautical publications you can find tables for calculating the dew point. Here is an example of such a table: In the left column you find the air temperature in Celsius, and at the top of the table you find the relative humidity in percent. We assume that the temperature is 27 degrees Celsius and the relative humidity is 60 percent. The intersection of the two figures shows that the dew point is reached at a temperature of 18 degrees Celsius or lower. It is a good practice to calculate your dew point at least every hour when you navigate in areas which are known for developing fog.

Main types of fog-radiation fog

There are four main types of fog: radiation fog, advection fog, frontal fog and sea smoke. Radiation fog is formed in a clear sky and adjacent to rapidly cooling land. The land will cool the air above it, causing water vapor to condense into droplets. Radiation fog first forms in valleys, and during the early morning it can even expand several miles out to sea. Rivers and estuaries may also be affected. When the sun rises and the land starts to heat up, radiation fog quickly disperses. In situations where the land takes longer to heat up, for example, when it is overcast, radiation fog may persist.

Advection fog

Advection fog, also known as sea fog, is formed when moisture-laden warmer air blows over colder land or water. When the warm air cools down to its dew point, water vapor in the air condenses and fog forms. Advection fog is very thick and persistent. It will only disperse when there is a change of wind which brings drier air.

Frontal fog

Frontal fog is usually found ahead of warm fronts and occluded fronts, and behind cold fronts. When warm moist air rises over colder air it causes the air temperature of the warm air to fall below its dew point. Frontal fog is not persistent, but can cause obstruction of landmarks.

Sea fog

Sea smoke is formed when cold air flows over a warmer sea. The cold air absorbs moisture, and the excess moisture, which cannot be absorbed, condenses immediately into fog. Simultaneously, the air is warmed by the sea and its dew point rises, dispersing the fog. Then the warm air rises and is cooled by the air at higher levels, and fog is formed again. Sea smoke does not persist for a long time. It forms, disperses and reforms constantly until the air adjacent to the sea is adequately warmed.

Weather information sources

Weather information sources 1

Before you proceed to sea and while you are at sea, it is highly important to stay informed about the current and imminent weather conditions. The latest weather information is crucial for the safety of the crew and the vessel. Severe weather can be avoided, and the risk of injury and damage can be reduced. Weather forecasts should be obtained at regular intervals. Let’s have a look at various sources of weather information. Before you go to sea, you can obtain weather information from newspapers, TV and the Internet.

Weather information sources 2

When your are sailing near the coast, weather forecasts can be received from certain National Weather Broadcast Frequencies on VHF radio. The broadcasting range is usually up to 40 nautical miles. When you are sailing offshore you can use a Navtex receiver to obtain meteorological forecasts and warnings at a distance of up to 400 nautical miles. Also, a Single Side Band weather fax receiver can be of great assistance. Under the right conditions it has a reception range of 6000 miles. In addition, you may utilize the satellite communication system to receive vital weather information.

Beaufort Scale

Introduction

In former times, when no wind measuring equipment was available, the Beaufort Scale was the only device available to determine the wind force. The scale was invented in the year 1805 by Sir Francis Beaufort and officially adopted in 1838. Sir Francis Beaufort sailed for many years in the British Royal Navy as a Commander. The first Beaufort Scale was originally related to tall ships and their sails. Later on it was modified to imply the effects of wind on land and sea.

Description

Let’s have a closer look at a modern Beaufort Scale. The scale contains a column with: the Beaufort Wind Force, the Mean Wind Speed in knots, the Descriptive Term, the State of Sea, and the probable Height of Waves in meters. The column with the probable Height of Waves in meters is added, and displays approximately the wave height that might be encountered in the open seas.

Interpreting a weather FAX

Introduction

Weather faxes provide the latest meteorological and oceanographic information available worldwide. They can be received with a Single Sideband Radio. The following key weather and sea charts are useful to mariners: · Surface charts · Sea state analysis · Wind and Wave charts · Sea surface temperatures · Satellite imagery and · Ice charts

Satellite imaginary-ice charts

Satellite imagery provides you with cloud cover and tropical cyclone information. Storms can easily be identified because of the large amount of clouds they produce. Ice charts show mainly location of ice, types of ice, thickness of ice and known icebergs. Here is an example of a 5 day sea ice forecast. On the right side you have detailed information concerning the ice.

Sea state analysis chart

The sea state analysis chart shows characteristics of sea waves and direction of movement. These observations are normally made a few hours before broadcast time. The combined sea heights are depicted in solid contours. The relative maxima or minima combined sea state values are enclosed in a box. The arrows indicate the direction of sea waves.

Surface charts 1

Surface charts provide mariners with the principal tool for a basic understanding of the present and upcoming weather. Let’s have a closer look at surface charts, differentiating between the surface weather analysis and the surface weather prognosis. The surface weather analysis shows weather patterns based on synoptic surface observations. These are usually made a few hours before broadcast time. The surface weather prognosis shows future weather patterns on a 12, 24, 36 and sometimes even a 72 hour forecast basis.

Surface charts 2

Here is an example of a 24 hr surface forecast chart. On this chart we can see the isobar lines, warm and cold fronts, the central pressure millibar values of synoptic scale lows and highs and their position in 24 hours. The 24 hour forecast position for lows are identified with vector arrows and an X, and for highs with vector arrows and an X with a circle around them. Adjacent to the forecast positions you can find the 2 digit pressure in millibars, which in this case is 29, which means 1029 millibars.

Wind and wave charts-sea surface temperatures

The wind and wave chart shows characteristics of sea waves and wind. The combined sea heights are depicted in solid contours. The relative minima or maxima combined sea state values are enclosed in a box. Wind speed and direction are also indicated. The wind speed is shown in knots. Each bar indicates 10 knots and each half bar 5 knots. Sea surface temperature charts show mean temperature values for a week, 10 days or a month. Ice edges are also depicted. Some transmissions also contain sea temperature anomalies.

Barometer

Introduction

The weight of air pressing down on the earth is called the air pressure. Air pressure is caused by the earth’s gravity, which acts like a downward force. Pressure can be measured by a barometer and can be recorded by a barograph. Pressure readings can be used to predict: storms,low pressure areas, high pressure areas,weather fronts,and wind fields. The barometer is the most useful weather forecasting tool for small vessels. There are two types of barometers, mercury and aneroid.

Aneroid barometer

Small vessels most often use an aneroid barometer. Although it is not as accurate as a mercury barometer, it is more robust, compact and affordable. The aneroid barometer consists of a corrugated container nearly exhausted of air, with a spring inside, along with a lever, a pointer and a graduated dial. When air pressure increases, the top of the corrugated container bows in, and when air pressure decreases, the top of the corrugated container bows out. The lever transmits these changes to the pointer on a dial. Air pressure can be measured in inches of mercury or in millibars, also known as hectopascals.

Aneroid barometer corrections 1

The aneroid barometer needs to be regularly corrected for index error and height above sea level. The index error is mainly caused by mechanical factors, and consequently the aneroid barometer slips from its initial accuracy. You should regularly check the accuracy of your aneroid barometer against a corrected mercury barometer. For information about mercury readings, call any national weather information service.

Aneroid barometer corrections 2

Because the air is denser at sea level than at higher altitudes, you must also correct for the actual height above sea level. Use the table "correction of millibar barometers to mean sea level" for the altitude correction. This table is available in the Nautical Almanacs. Let’s look at how to apply the correction. First, note your barometer reading, the air temperature and your actual height above sea level. Let’s assume that the barometer reading is 1015.4 millibars, the air temperature is 20 degrees Celsius and your height above sea level is 5 meters. By applying the air temperature and height above sea level to the chart, you see that the correction is 0.6 millibars. Add this figure to your barometer reading. Hence, the barometer reading corrected to mean sea level is 1015.4 millibars plus 0.6 millibars, which equals 1016 millibars. Keep in mind that the greater the height above sea level and the greater the temperature, the greater your correction to mean sea level will be.

Barograph

A barograph is a type of aneroid barometer, and as you see here, the pointer is replaced by a pen. It also has a drum and bellows. Every seven days the drum makes one revolution. A chart, which is affixed to the drum, is graduated in time on one axis and atmospheric pressure in millibars on the other. The barograph provides a continuous record of the atmospheric pressure. Since the barograph can be affected by environmental factors, its location should be carefully selected. Place it in a position that is, as far as possible, free from vibration, loud noise, jostling and gusts of air. The barograph should be fastened in an athwartships position, so the pen does not leave the paper when the ship is rolling.

Anchoring

Types of anchors

Make sure that you carry at least two anchors, one as an everyday anchor that is stowed at the bow in the anchor locker, and one as a storm anchor. The characteristics of the boat and the type of bottom - sand, shale, mud, gravel - affect the type of anchor you should use. Commonly available anchors are: The Plow type anchor, which provides very high holding power by digging itself into bottom sediments. The plow type is also effective on weedy bottoms. The Fluke type anchor, which provides very good holding power by burying itself into bottoms of sand or mud, but not so good in rocks or kelp. It is lightweight and can be stowed flat, but can be difficult to remove from mud. The Fisherman - type anchor, which has diamond-shaped flukes that makes the anchor function efficiently as a "rock pick". It must be large and heavy to be most effective and can penetrate and hold in weeds, gravel, or rocks. It folds flat for stowage.

Before anchoring 1

When you are selecting a position for anchoring, make sure that it is sheltered from the wind and waves, and away from boat traffic. Check the chart to determine the depth where you want to anchor, and calculate the amount of cable you should put out. At a minimum, you should pay out (for rope cable with a length of chain) five times the depth of the water in which you wish to anchor plus the distance from the water to the bow where the anchor is attached. For example, if you measure a water depth at 7 meters (23 feet) and the distance from the water to the bow where the anchor is attached is 1 meter (3,2 feet), then the total distance of 8 meters (26.2 feet), should be multiplied by five to get the amount of cable to pay out. The result is 40 meters (131 feet) of cable. For chain cable the minimum ratio is 3 to 1 The deeper the water, and the more severe the weather, the more cable you will need to pay out.

Before anchoring 2

Before anchoring among other boats, consider your boat's swinging circle. When the wind shifts or the current changes, your boat will swing bow to the wind or current, whichever is stronger. Try to anchor your boat near boats of similar size and type, which should swing at a similar rate. Different types of boats will swing at different times, depending on the tide, the strength and the direction of the wind. Choose a proper holding ground - the best holding grounds are of mud, sand or clay, or a mixture of them. Between the anchor line and the anchor you must insert a length of chain, approximately 4 meters (16,4 feet). It will help the anchor to 'dig in' and not drag.

Anchoring with one anchor 1

Anchoring with one anchor: On the Nautical chart, select and mark the position at which you intend to anchor. Make your approach slowly into the wind or current, whichever is stronger, to the spot you have selected. Stop the boat and drop the anchor, allowing it to reach the bottom. Then slowly back the boat away, downwind or down current to stop the chain and/or rope from piling up. Using the rudder by means of the wheel, and the engine by means of the throttle, steer the boat and lay out the cable along the bottom . To make sure that you don’t drag your anchor after anchoring, it is essential to check your position periodically. To do that take compass bearings, using transits if possible and if you have radar check ranges from shore. If the reference points and ranges you take stay the same, then you are not dragging your anchor. Establish anchor watch during your stay at the anchorage to make sure you’re not drifting.

Anchoring with one anchor 2

After anchoring, if you find that you are dragging the anchor try to let go more cable. If that doesn't work, heave up the anchor and try to anchor in somewhere else. When you want to depart the anchorage, heave up the anchor while you are pulling on the line or powering your boat until the cable hangs vertically at the bow. Then secure the cable as the boat moves slowly ahead and past the vertical line position. That will help to use the weight of the boat to free the anchor from the bottom. As soon as the anchor is clear, bring it up to the water line and make sure it is free of other cables or lines before you speed up the boat. Never drag the anchor behind the boat.

Anchoring with two anchors

In this lesson you will learn to anchor using two anchors. There are two popular methods that cover most situations: a) Anchoring with the anchors set 180 degrees from each other and b) anchoring with the anchors set 45 degrees off the bow. Anchoring by setting the anchors 180 degrees from each other reduces the swinging circle and works very well when the wind direction remains constant or changes direction 180 degrees , or on a current that reverses direction, or on a narrow stream. Anchoring while you set the anchors 45 degrees off the bow improves holding power. One anchor works as a backup if the other drags, and the load is shared between the two anchors. This also works well when the wind significantly changes direction.

Anchors 180 degrees from each other

Anchoring while you set the anchors 180 degrees from each other Let's assume you select the anchoring position, and after calculations, the length of the cable you should pay out is 30 meters (98 feet) for each anchor. Make your approach slowly into the wind to the spot you have selected, stop the boat and drop the forward anchor. Then slowly back the boat away downwind, while you payout twice the length of the cable needed

Anchors 45 degrees off the bow

Anchoring while you set the anchors 45 degrees off the bow. Let's assume you select the anchoring position, and after calculations, the length of the cable you should pay out is 30 meters (98 feet) for each anchor. Make your approach slowly into the wind to the anchoring spot you have selected. Note the compass heading, (let's assume it was 360 degrees or north), and turn to starboard till your compass heading shows 022 to 024 degrees, and move forward on that course for approximately 30 meters. Stop the boat and drop the starboard anchor. Slowly back the boat away downwind, while you pay out the calculated cable until you are back to the anchoring spot you have selected. The next step is to turn the boat to port until your compass heading shows 336 to 338 degrees. Move forward on that course for approximately 30 meters while you pay out cable from the starboard anchor and drop the port one. Slowly back the boat away downwind while you pay out the calculated cable, and heave up the slack from the starboard one until you are back to the anchoring spot you have selected. Using this method the boat will be anchored while the anchors are set 45 degrees off the bow with equal lengths of cable. Good seamanship calls for tying each cable to a different cleat in case you have to release one of them.

Anchoring houskeeping

Store the anchors below deck in the anchor locker. Make sure that the anchor is well secured and tied, as a loose anchor can cause a lot of damage. Use a small fender as a wedge to protect the anchor from banging or rattling. Make sure that the anchor locker is dry at all times, the drain is clear from obstructions and the watertight gaskets are in place and in good condition. Sailing into a rough sea with water in the anchor locker will put the boat down by the bow and it will be difficult to steer.

Tripping line

When you are berthing stern - to, if you have any doubts concerning unknown obstructions at the bottom of the sea, or if you have to anchor in a crowded anchorage, it is better to attach a tripping line to your anchor. The tripping line is a light buoyed line with one end attached to the crown or to the eye on the back of the anchor, and the other end made fast on a buoy. Make sure that the buoy is clearly marked, and indicate that it is attached to a tripping line, for example by painting a large anchor on the side of the buoy, so other boats will not moor up to it. To free the anchor from any obstruction use the tripping line until the anchor is clear.

Safety at sea

Introduction

Fire prevention is the best way to fight a fire. Therefore it is important to know what may cause a fire, and where it could start. The most common areas where fires originate are the galley, the electrical panels and the engine room. Possible causes are: electrical faults, cabin heaters, electric motors, or an explosion in the gas or fuel supply.

Vital Tips 1

Good housekeeping is necessary in order to prevent a fire. Here are some vital tips: 1. Maintain a stringent non-smoking policy. 2. Keep flammables, such as clothing and paper, away from radiators. 3. Be sure small appliances are unplugged when not in use. 4. Do not overload outlets with too many outlet adaptors and/or extension cords. 5. Never run cords under rugs. 6. Be sure nothing is in contact with a light bulb. 7. Keep the engine room clean. 8. Check for fuel and oil leaks.

Vital Tips 2

Here are more vital tips for fire prevention: 1. Store dirty rags with oil or paint in closed metal containers until you dispose of them. 2. Check that wiring is properly secured and protected from chafing. 3. Keep flammable liquids in their original containers and store them away in properly ventilated, secured areas. 4. No open flames near gas appliances. 5. When refueling, shut down the engine and all other machinery. 6. Install a gas detector with a warning bell. 7. Install smoke detectors in each compartment.

Classes of fire

To extinguish a fire properly, you have to know what is burning. A fire involving wood must be handled differently than a fire involving petrol. Therefore fire is divided into 6 classes: Class "A" fires involving ordinary combustible materials such as wood, cloth, plastic and paper. Class "B" fires involving flammable liquids or flammable solids such as grease, paint, oil, petrol, varnish and fat. Class "C" fires involving gases such as butane, propane, acetylene. Class "D" fires involving burning metals such as magnesium, titanium, potassium. Class "E" fires involving electrical hazards. Class "F" fires involving flammable liquids such as deep fat fryers. A class "D" fire should only be tackled by qualified personnel trained in the handling of this class of fire.

Introduction-water-dry powder extinguisher

Fire extinguishers are categorized by the class of fire that they will extinguish, and by the substances they contain. They are labeled with capital letters according to the class of fire. Extinguishers may be rated for only one class, or for multiple classes. Let’s have a closer look at the various extinguishers. Water extinguisher: A water extinguisher cools and dampens the fire. Water removes the heat element from the fire triangle. Use the water extinguisher when you have a class "A" fire. Never use water on a class "B", "C", "D", "F" or "E" fire . Dry powder extinguisher: A dry powder extinguisher puts the fire out by separating the burning substance from the oxygen, and also interrupts the fire’s chemical reaction. Use this extinguisher for class "A", "B", "C" and "E" fires. Check the labeling on dry powder extinguishers. Some may only be good for classes "B" and "C".

CO2 extinguisher-foam extinguisher

Co2 extinguisher: A carbon dioxide (Co2) extinguisher causes the fire to suffocate. Co2 removes the oxygen element from the fire triangle. Use this fire extinguisher for class "B" and "E" fires. Never use a Co2 extinguisher for class "C" and "D" fires. Foam extinguisher: A foam extinguisher cools the fire, thus removing the heat element from the fire triangle. Foam also prevents re-ignition by smothering the fire. Use this fire extinguisher for class "A" and "B" fires.

Using an extinguisher

It is of utmost importance that you use an extinguisher only for the class of fire it is approved for! Using the wrong fire extinguisher could cause a greater problem, such as spreading the fire further. Or, using the wrong type of extinguisher may cause harm to the fire fighter. Portable fire extinguishers are not designed to fight large or spreading fires. But they can be useful when the following conditions are met: 1. The operator must know how to use the extinguisher. 2. The extinguisher must be classified for the fire the operator wants to fight. 3. The extinguisher should be within easy reach. 4. The extinguisher should be fully charged. 5. The extinguisher should be working properly. 6. The extinguisher should be large enough to extinguish the fire. 7. The operator must have a clear escape route before he starts tackling the fire.

How to use a fire blanket

Fire blankets are made of fire resistant materials. They are especially useful for putting out galley pan fires or for wrapping a person whose clothing is on fire. A fire blanket should be mounted close to the galley, but not in the galley, so it can still be reached during a galley fire. How to use a fire blanket: In case of a galley pan fire, hold the blanket in front of you and slowly approach the source of fire. Cover the burning material completely with the blanket. Then switch off the source of heat. Keep the fire covered until the oil or fat is cool. The blanket can be removed after cool down. Do not remove the blanket when the oil is still hot since re - ignition can occur.

Introduction

Distress signals are used when a boat or a crew member is in danger and requires assistance. Several devices can be used to attract the attention of possible rescue units: a radio, an EPIRB, a radar transponder, pyrotechnics, flags, and signals. Which device is the best to use depends on the circumstances. If the visibility is good and the rescuers are close by, you could use hand flares, or if you are far away from land maybe it is best to activate the EPIRB.

By radio

The most common way of sending a distress signal is by radio. Modern radios conform to the GMDSS (Global Maritime Distress and Safety System). GMDSS is an international system that uses terrestrial and satellite technology and ship board radio systems to allow rapid response in an emergency situation. Nowadays distress messages can be initiated digitally by pressing the call button on the radio set. Radio sets which are not according to the GMDSS standard transmit a distress message by voice on channel 16 on a VHF transmitter, or on 2182 kHz on an MF transmitter. The reception range of a VHF transmitter to a coastal station averages 35 nautical miles and between an MF transmitter and a coastal station 150 nautical miles. If you or your vessel is in grave and immediate danger use the MAYDAY call. MAYDAY is the internationally recognized radiotelephony distress signal for a person or a vessel in imminent danger.

Distress pyrotechnics

Distress pyrotechnics come in various types: handheld, buoyant, or as parachute rockets. The red parachute rocket is designed for long - range signaling. During the day the visibility of the flare is up to 8 nautical miles and at night up to 21 nautical miles. The rocket carries its payload to a height of 984 feet and then ejects a red flare. The burning time is 40 seconds at 30.000 candelas. The red hand flare is used for short - range signaling situations. During a clear dark night the visibility of the flare is 5 nautical miles at sea level and 10 nautical miles from an aircraft. In daylight the visibility is reduced. The burning time is 60 seconds at a min. of 15.000 candelas, and the flare is red. The buoyant orange smoke signal is used in daylight only, to pinpoint the distress position to a searching aircraft. It emits dense orange smoke for about 2 minutes. It is very important to read the instructions for use on each distress signal carefully. Store your signaling devices in a marked watertight container which should be readily available. All pyrotechnics are equipped with a date of expiration. Replace expired pyrotechnics as they become less reliable. To dispose of them, return them to the manufacturer or to the nearest coast guard station.

EPIRB

Another very important aid to one - way radio communication is the EPIRB. EPIRB stands for Emergency Position Indicating Radio Beacon. The EPIRB transmits the distress alert to a satellite. The satellite locates the EPIRB's position and relays the information to a Land Earth Station, and in turn the Land Earth Station relays the information to a rescue coordination center. EPIRBs contain an optional 121.5 MHz homing beacon. This homing device facilitates Search and Rescue Helicopters with VHF direction finders. The EPIRB is also fitted with a hydrostatic release unit, Which, if the vessel sinks, releases at a certain depth the EPIRB automatically from its stowage position. When the EPIRB emerges on the surface it will automatically start the distress alert.

SART

SART stands for Search and Rescue Transponder. It is a device for locating ships or their survival craft in distress. The SART operates in the 9 GHz frequency band - generating a series of dots when being interrogated by a search craft with an X - Band (3cm) radar. As the search craft approaches to within 1 nautical mile of the SART, the 12 dots change to wide arcs and eventually into complete circles as the search craft nears the SART. For the person in distress the SART provides a visual and acoustic indication when being interrogated. The detection range from a rescue ship to the SART is a minimum of 5 nautical miles, and from a Search and Rescue helicopter up to 40 nautical miles.

Signaling Flags

When in sight of another vessel and no flares or radio are available you can use the signaling flags to call attention to a distress situation. If you require assistance you can use the Code Flag "Victor". Hoist the Code Flag "November" above the Code Flag "Charly" or a black square over a black ball if you are in imminent danger and immediate assistance is required . Code Flag "Whiskey" is used if you require medical assistance. Sound signals made with a whistle or a gong can also be helpful in attracting attention. If no signaling device is available use your arms. Stand facing in the direction of assistance and slowly raise and lower your arms. A combination of flags, audio and arm signals can be used to attract attention. CLICK ON THE PICTURES TO ENLARGE

Mayday call

Start a MAYDAY CALL procedure as follows: Check that the main battery switch is on

Navigation Lights

Navigation lights introduction

Navigation lights are used to prevent collisions at night or in times of reduced visibility. Vessels are required to show the proper navigation lights from sunset to sunrise in all weather conditions and in conditions of reduced visibility. All vessels must display basic navigation lights. These lights indicate: - Whether a vessel is under sail or power. - The direction of the vessel. - The likely size. - The activity. Additional specific sets of lights are used by vessels to indicate that they are engaged in a specific job or that they are under restrictions.

Basic navigation lights

According to the International Regulations of Preventing Collisions at Sea (ColReg), navigation lights have a specific - color (white, red, green, yellow or blue), - arc of illumination, - range of visibility and - location. The basic navigation lights are: - The masthead light is a white light, placed over the fore-and after-centerline of the vessel and that is visible over a 225°arc. From dead ahead to 22.5° abaft (behind) the beam on both sides of the vessel. - The All-round light is a light, with the color determined by its use and is visible over a 360° arc. - The sidelights are colored lights - red on port and green on the starboard side of the boat and is visible over a 112.5° arc, from dead ahead to 22.5° abaft the beam on each side. - The stern light is a white light, centered on dead astern, and is visible over a 135° arc. The side lights can be combined in one lantern at the bow. The sidelights can be combined with the stern light in a tricolour light at the masthead. - The towing light, is a yellow light and is used in a towing operation. Centered on dead astern vertically above the stern light and is visible over a 135° arc. - The flashing light is a yellow or blue flashing light with minimum 120 flashes per minute and is visible over a 360° arc.

Vessels under 7 meters (23 feet)

NON-POWERED VESSELS UNDER 7 METERS, (23 feet): Non-powered vessels, such as rowboats, canoes, and sailboats under 7 meters (23 feet), in length may use a flashlight for navigation. The light does not have to be turned on at all times, but should be turned on in time to avoid a collision. When under motor, and the speed is less than 7 knots, these vessels shall exhibit a fixed all-round white light, with visibility of two nautical miles, also sidelights, with a visibility of one nautical mile.

Vessels under 12 meters (39 feet)

VESSELS UNDER 12 METERS, (39 feet): Sailboats: A sailboat under sail and under 12 meters (39 feet) shall exhibit: - Separate sidelights or a single "bicolor" light, visibility of one nautical mile - A stern light, visibility of two nautical miles. The sidelights and the stern light may be combined in a tricolour light placed at the masthead. Motorboats: A motorboat under 12 meters (39 feet) shall exhibit: - A mastheadlight, with visibility of two nautical miles, placed at least one meter over the sidelights. - Separate Sidelights or a single "bicolor" light, with visibility of one nautical mile - A stern light, with visibility of two nautical miles. The mastheadlight and the stern light may be replaced with an all-round white light, visibility of two nautical miles.

Vessels under 20 meters (65 feet)

VESSELS UNDER 20 METERS, (65 feet): Sailboats: A sailboat under sail and under 20 meters (65 feet) shall exhibit: - Separate sidelights or single "bicolor" light, with visibility of two nautical miles - A stern light, with visibility of two nautical miles. The side lights and the stern light may be combined in a tricolour light placed at the masthead. - In addition they may also display a red and green all-round light, the red being the top light, with visibility of two nautical miles. In this case the sidelights and the stern light must be separate (not in tricolor combination). A sailboat under sail when also being propelled by machinery shall exhibit forward where it can best be seen a conical shape, apex downwards. A vessel of less than 12 meters in length is not required to exhibit this shape, but may do so. A Sailboat under power is considered to be a powerboat and must follow the rules of the road for powerboats. Motorboats: A motorboat less than 20 meters (65 feet) shall exhibit: - A mastheadlight, with visibility of three nautical miles, placed at least 2,5 meters over the upper deck. - Separate sidelights or a single "bicolor" light, with visibility of two nautical miles. - A stern light, with visibility of two nautical miles.

Vessels over 20 meters (65 feet)

VESSELS OVER 20 METERS, (65 feet): Sailboats: A sailboat under sail and over 20 meters (65 feet) shall exhibit: - Separate Sidelights - A stern light. The sidelights and the stern light may NOT be combined in a tricolour light. - In addition they may also display a red and green all-round light, with the red being the top light. Motorboats: A motorboat over 20 meters (65 feet) and less than 50 meters (164 feet) shall exhibit: - A mastheadlight, with visibility of five nautical miles positioned over the sidelights. - Separate Sidelights, - A stern light. When the motorboat is more then 50 meters (164 feet) it must show two mastheadlights, with visibility of six nautical miles with the forward mastheadlight positioned lower than the aft mastheadlight.

An air-cushion vessel

AN AIR-CUSHION VESSEL: An air-cushion vessel when operating in nondisplacement mode, in addition to the lights for a power driven vessel, shall exhibit: - An all-round flashing yellow light, where it can best be seen.

A towing vessel

A TOWING VESSEL: Towing vessel when in operation shall exhibit: - Two masthead lights in a vertical line. When the length of the tow, measuring from the stern of the towing vessel to the aft end of the tow exceeds 200 meters, three such lights in a vertical line. - Separate sidelights - A stern light - A towing yellow light in a vertical line above the sternlight - A diamond shape where it can best be seen. A vessel or object being towed, shall exhibit: - Separate sidelights - A sternlight - When the lenght of the tow exceeds 200 meters, a diamond shape where it can best be seen.

A fishing vessel engaged in trawling

A FISHING VESSEL ENGAGED IN TRAWLING: A fishing vessel engaged in trawling shall exhibit: - Two all-round lights in a vertical line, the upper being green and the lower white, in the day time a shape consisting of two cones with their apexes together in a vertical line one above the other. - A masthead light abaft of and higher than the all-round green light, a vessel of less than 50 meters in length shall not be obliged to exhibit such a light but may do so. - When making way through the water in addition, sidelights and a sternlight.

A vessel engaged in fishing

A VESSEL ENGAGED IN FISHING: A vessel engaged in fishing shall exhibit: - Two all-round lights in a vertical line, the upper being red and the lower white, in the day time, a shape consisting of two cones with their apexes together in a vertical line one above the other. - When there is outlying gear extending more than 150 meters horizontally from the vessel, an all-round white light, in the day time, a cone apex upwards in the direction of the gear. - When making way through the water in addition, sidelights and a stern light.

A vessel not under command

A VESSEL NOT UNDER COMMAND: A vessel not under command shall exhibit: - Two all-round red lights in a vertical line where they can best be seen. - By day two balls or similar shapes in a vertical line where they can best be seen. - When making way through the water, in addition, sidelights and a sternlight.

A vesssel restricted in her ability to manouevre

A VESSEL RESTRICTED IN HER ABILITY TO MANEUVER: A vessel restricted in her ability to maneuver shall exhibit: - Three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white. - By day, three shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond. - When making way through the water, in addition a masthead light or lights, - Sidelights, and - A sternlight. A vessel engaged in dredging or underwater operations, when restricted in her ability to maneuver, shall exhibit the above lights and shapes. When an obstruction exists, in addition, shall exhibit: - Two all-round red lights and by day two balls in a vertical line to indicate the side on which the obstruction exists. - Two all-round green lights and by day two diamonds in a vertical line to indicate the side on which another vessel may pass.

A vessel engaged in diving operation

A VESSEL ENGAGED IN DIVING OPERATIONS: A vessel engaged in diving operations shall exhibit: - Three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white. - The international code's flag “A”, not less than 1 meter in height. Measures shall be taken to ensure its all-round visibility.

A vessel engaged in mine clearance operation

A VESSEL ENGAGED IN MINE CLEARANCE OPERATION: A vessel engaged in mine clearance operation shall in addition to the lights for a power driven vessel, exhibit: - three all-round green lights or three balls. One of these lights or shapes shall be exhibited near the foremast head and one at each end of the fore yard. - These lights or shapes indicate that it is dangerous for another vessel to approach within 1000 meters of the mineclearance vessel.

A vessel constrained by her draft

A VESSEL CONSTRAINED BY HER DRAFT: A vessel constrained by her draft, in addition to the lights for a power driven vessel, shall exhibit: - Three all-round red lights where they can best be seen in a vertical line, - By day a cylinder.

A vessel engaged on pilotage

A VESSEL ENGAGED ON PILOTAGE: A vessel engaged on pilotage shall exhibit: - At or near the masthead, two all-round lights in a vertical line, the upper being white and the lower red, - When underway, also sidelights and - A sternlight.

A vessel at anchor

A VESSEL AT ANCHOR: A vessel of more than 50 meters in length, and at anchor shall exhibit where it can best be seen: - In the fore part, an all-round white light - At or near the stern, an all-round white light placed at a lower level than the forward light, and - By day one ball. A vessel of less than 50 meters in length, at anchor shall exhibit: - An all-round white light where it can best be seen, and - By day one ball. A vessel at anchor may, and a vessel of 100 meters and more in length shall, also use the available working or equivalent lights to illuminate her decks.

A vessel aground

A VESSEL AGROUND: A vessel aground shall exhibit: - An all-round white light in the fore part, - At or near the stern, an all-round white light placed at a lower level than the forward light, - Two all-round red lights in a vertical line, - By day three balls in a vertical line. A vessel of less than 50 meters in length, shall exhibit where it can best be seen: - An all-round white light in addition, - Two all-round red lights in a vertical line, - By day three balls in a vertical line.

Identify the lights

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Lights and shapes

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Signals

Test

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GMDSS

Introduction

The Global Maritime Distress and Safety System (GMDSS) was developed by the International Maritime Organization (IMO). GMDSS is an internationally recognized distress and radio communication safety system. The system uses satellites and digital selective calling technology to provide an automatic means of receiving and transmitting distress alerts. The GMDSS system is primarily a vessel-to-shore alerting system. The Rescue Coordination Centers (RCCs) receive distress alerts from ships and then coordinate the rescue. The system also provides a vessel-to-vessel distress-alerting feature. Other types of messages that could be transmitted by the system are: urgency, safety and routine communications and safety information broadcasts, e.g. (navigation warnings, weather forecasts and rescue messages).

Coverage areas

GMDSS uses 4 coverage areas: A1, A2, A3 and A4. These areas together cover the sea areas of the world. Sea Area A1 is an area within Very High Frequency (VHF) range of a coast station fitted with Digital Selective Calling (DSC). This range is about 30 to 40 miles. Sea Area A2 is an area with Medium Frequency (MF) range of a coast station fitted with DSC. This range is about 150 miles. Sea Area A3 is an area covered by the Inmarsat Satellite System, excluding Sea Areas A1 and A2. Sea Area A4 is basically the polar regions that are not covered by the other Sea Areas.

Equipment needed

Depending on how far from shore you will operate your craft, the following minimum GMDSS equipment should be on board. Remember, you are not limited to having only the minimum recommended devices. In an area of operation up to 5 miles from shore it is recommended to have a handheld waterproof VHF radio on board. In an area of operation up to 30 miles from shore, a handheld waterproof VHF radio and a VHF DSC fixed radio installation. Up to 60 miles from shore, a handheld waterproof VHF radio, a VHF DSC fixed radio installation and a NAVTEX receiver. Up to 150 miles from shore, a handheld waterproof VHF radio, a VHF DSC fixed radio installation, a NAVTEX receiver, an EPIRB, a MF DSC radio installation and a SART. Over 150 miles from shore, it is recommended that you have a handheld waterproof VHF radio, a VHF DSC fixed radio installation, a NAVTEX receiver, an EPIRB, a MF DSC radio installation, a SART and Inmarsat Satellite Communication.

Radar

Description

Radar is the acronym for Radio Detection and Ranging. But how does radar work? Radar transmits short pulses of radio waves that travel outward, basically in straight lines. When these waves hit a surface, like a vessel or a buoy, some of the waves are returned. By measuring the time difference between transmission and reception of a reflected wave, the distance to an object can be calculated. The direction in which the scanner is pointing when it receives the reflected wave represents the bearing of the object.

Basic components

Radar systems comprise three basic components: A transmitter and a receiver unit, also called a transceiver, an antenna, also known as a scanner, and a display unit. In many radar units the transceiver is located in the scanner. Radar signals travel along the "line of sight". Therefore the detection of targets depends on the height of the radar scanner and the height of the target. Marine radars operate either on the X-band frequency (9000 MHz), or on the S-band frequency (3000 MHz). A shorter wavelength allows the use of smaller antennas, therefore on most small boats the radar used are on the X-band frequency. However, S-band radar has an advantage - it can penetrate precipitation better, and therefore can detect targets better, for example, in heavy rainfall.

Radar controls general

This is a radar display unit. This display unit has controls for the following purposes: The function control. Range selector. The brilliance control. The tuning control. The tuning indicator. The gain control. The anti-clutter sea control and the bearing cursor ring. Review the controls. Use the mouse to rollover them.

The function control

The function control has five positions, which are: Radar off position. At this position the radar is not in operation and there is no power supplied to the display or to the scanner. Standby position. In this position the radar can be brought into use whenever required. The scanner is rotating, but no radio waves are being transmitted. Radar on position. In this position it takes 2-4 minutes for the radar to be in full operation. Radio waves are being transmitted and the received echoes from targets are amplified and displayed on the screen. Range Rings/Bearing Cursor. In this position the range rings on the screen are illuminated together with bearing cursor and the bearing scale window. Heading alignment position. In this position the picture of the screen synchronises with the aerial and brings the heading marker in position. Click on the green arrowson top of the functioncontrol knob!

Other Radar controls

Range selector position. The range selector is used to select the range for the radar to cover. There are five positions, indicated in miles: 1½, 3, 6, 12, and 24 miles. When the range is selected, the distance between the rings is determined automatically. Brilliance control. By using this control, the background illumination of the screen can be adjusted. This allows better visibility of amplified echoes and noises appearing on the screen. Tuning control. This control allows the receiver to be tuned to the same frequency as the transmitter. Tuning indicator. This is a visual electronic aid that helps to tune the radar quickly and accurately. Adjustment of the knob to display the narrowest gap corresponds to optimum tuning. Gain control. This control allows the user to vary the strength of echoes appearing on the screen. Anti-Clutter sea control. The main use of this control is to reduce the strength of sea clutter ( echos from waves), near the ship, so strong targets e.g. small craft, buoys, etc., can be better distinguished. This control reduces the gain level only over a short range. The knurled ring is used to rotate the bearing cursor over the face of the screen, which allows the user to measure the bearings of the targets.

Echo sounder

Introduction

The echo sounder is an important and necessary electronic navigation instrument that determines the depth of water under the keel. This is one of the prime considerations for safe navigation. An echo sounder consists of the transducer and the display. The transducer transmits ultrasonic waves through water. The wave strikes the seabed and part of the wave is then reflected back and received by the transducer. Knowing that the ultrasonic wave travels through water at a nearly constant speed of 1500 meters (4921 feet) per second at a temperature of 13°C at a salinity of 35 (35 parts per thousand), the depth can be determined by calculating the time difference between the transmission and the reception of the ultrasonic wave. The determined depth information is converted into visual or graphic form.

Operation performance

Satisfactory echo sounder performance depends primarily on the transducer installation. The most common transducer installation is a transom mount. The transducer should be mounted at the bottom of the hull as close to the keel as possible and 1/3rd aft so that turbulent water from the bow and propeller noise do not affect its performance. The transducer should preferably be mounted on the side of the boat where the propeller chops down into the water to avoid aeration and turbulence. Performance can also be negatively affected if the transducer is mounted near engines, alternators, or seawater inlets and outlets.

Echo sounder controls

The most common and basic echo sounder controls are: The illumination control, which regulates the illumination of the panel and other controls. The range selector that selects the basic ranges according to the technical specifications. In position 0 (zero) the echo sounder usually switches off. The gain control, which regulates the amplification of the received signals. Using the gain control, we can eliminate the multiple echoes that appear when navigating in shallow waters.

Main types

There are three main types of echo sounders: The neon rotating display echo sounder, the echo sounder that produces a continuous record of the depth of the water using electrolyte paper and the digital echo sounder. Other echo sounders have multi-colour displays and show not only the depth of the water, but different types of sea beds, sunken wrecks, and even schools of fish.

Lead line

The simplest form of an echo sounder is a lead line, 60 feet long, attached to a 1 to 1,5 kilogram lead weight. In the base of the weight is a cavity used for taking bottom samples, which are useful when piloting or anchoring. The line has a series of marks along its length. When dropped into the sea bottom, the marks are used to measure the depth of water. Lead line can be used as a backup when there are concerns about the reliability of the echo sounder.

LORAN C

Introduction

Loran C is a hyperbolic navigation system which determines the position of a craft by the intersection of lines. Loran stands for Long Range Navigation. The Loran C carrier frequency is 100 kHz, and the waves which are traveling from transmitter to receiver are called Kilometric or Low Frequency. The 100 kHz frequency has the advantage of stable ground waves over long distances, however, delayed sky waves which are reflected from the Ionosphere may cause distortion of the signals.

Principle of operation 1

The Loran C system consists of groups of land - based transmitter stations, called chains. A chain contains a Master station and at least 2 Secondary stations. A Master station (M) commonly has 4 to 5 Secondary Stations named Victor, Whiskey, X-Ray, Yankee and Zulu. These stations can be separated by several hundred miles. To determine a position, a Loran C receiver must acquire signals from a Master station and 2 Secondary stations at the same time.

Principle of operation 2

The Loran C system usually has a position fixing accuracy of plus or minus 50 feet, except at sunrise and sunset, or during a passage of a strong weather front. The ground coverage ranges from 700 to 1000 nautical miles. The advantages of the Loran C system are: high repeatable accuracy, ease of operation and an affordable price. Disadvantages are: low initial accuracy, easily affected by noise, position fixing is only 2 dimensional, coverage is only regional, not world wide.

GPS

Introduction

The Global Positioning System (GPS) is a satellite - based navigational aid system placed into orbit by the U.S. Department of Defense. The system consists of 24 satellites, orbiting the earth twice a day at an altitude of about 12,000 miles. GPS satellites are powered by solar energy. With backup batteries are installed on board to keep them running in case of a solar eclipse. The system provides highly accurate worldwide positioning and navigation information 24 hours a day.

Satellite signal

A GPS satellite signal contains three different kinds of information: a pseudorandom code, ephemeris data and almanac data. The pseudorandom code is the Identification code of the satellite, which on a GPS receiver is displayed as a number. Ephemeris data contains information about the status of the satellite (healthy or unhealthy), current date and time. The almanac data informs the GPS receiver where each satellite is positioned at any time. The satellite transmitting the data contains orbital information for that satellite, and for every other satellite in the system.

Determine the position

But how is a position determined by satellites? A GPS receiver knows the position of the satellites by the data each satellite transmits. The receiver estimates how far away a satellite is, and knows that it is positioned somewhere on the surface of an imaginary sphere centered at the satellite. For each satellite the receiver determines the size of the sphere. The receiver is located where the spheres of the satellites intersect.

Obtaining a fix

To obtain a two-dimensional fix, i.e. latitude and longitude, three satellites are necessary. To obtain a three-dimensional fix, i.e. latitude, longitude and altitude, four satellites are necessary. The position accuracy of the GPS system lies between 5 and 15 feet. Differential GPS receivers obtain an even higher accuracy.

Differential GPS (DGPS)

Differential GPS (DGPS) works by placing a GPS receiver that is a reference station at a known location. The station measures the ranges to each satellite. Then it uses the measured ranges and the actual ranges calculated from its known position. Measured ranges can contain errors such as ephemeris data errors or internal receiver noise. The difference between measured and calculated ranges becomes a "differential correction". The differential correction is then transmitted to the DGPS receivers.

GPS components and controls 1

This is a GPS receiver. GPS stands for Global Positioning System. There are various components and controls used on the GPS receiver. The antenna, which receives the radio signals from the GPS satellites. The power button, which turns the power on and off. The light button, which lights the display for 20 seconds The display. The cursor control buttons, which move the cursor to input or select. And the character search buttons, which allow the user to select the characters to input, or to select a function.

GPS components and controls 2

On this GPS receiver we can also see: The Track button, used to enter the track mode. The Edit button, used to enter the EDIT mode. The Nav (navigation) button, used to access the position mode. The Set button, which allows control over the power-saving function. The clock display and the distance display. The Pos (position) button, used to enter the position mode. The Clear button, which allows deletion of any unnecessary data, and allows initialization of the receiver. The Enter button, which is used to enter data or execute a command. The Recall button, which returns the user to the previous display. The Mark button, which stores the present position and the extension display select button. By pressing this button in NAV and TRACK mode, the graphic or character display can be selected, and in POS mode the date and time will be displayed.

Review Interaction

Complete following task: 1. enter a waypoint with the name: DEPART 2. the coordinates are LAT: N 20° 30' 45.0" LONG: E 110° 10' 30.5" Start with the EDIT button!

Navtex

Introduction

Navtex is an automatic reception and broadcast system for maritime safety information. It uses the narrow-band direct printing telegraphy. It supplies the shipping with vital information, such as navigational and meteorological warnings and urgent information. This information is printed out or displayed automatically by dedicated receivers called Navtex receivers. Navtex is a part of the IMO (International Maritime Organization) and has been included in the Global Maritime Distress and Safety System (GMDSS).

Navtex broadcast

All Navtex broadcasts are made on 518 kHz from localized stations situated worldwide. Navtex users can set their receiver to specific message types, e.g. Ice reports or Satnav messages, and can reject others. However, navigational warnings and search and rescue information, including pirate attack warnings, cannot be rejected.