Vessel identities. Vessels identify one another either by their name or international call sign. The name is obviously given to the ship when it is launched. The call sign is allocated by the department issuing the vessel’s radio licence/certificate, usually by the country in which the ship is registered. A…
Radio communications are the the most commonly used means of communication today. It is the easiest to use and the most versatile. It requires no particular skill and it has tremendous range. In addition, it supports a multitude of types of communication, ie telephony (voice), telegraphy (morse), facsimile (reproduction of…
Pyrotechnics. By pyrotechnics is meant the use of flares of different colours as a means of conveying certain meanings. For example, if a vessel fires a red flare it means internationally that it is in trouble and requires assistance. The use of various coloured flares is mainly used by the…
Semaphore. Semaphore is a means of signalling employing two hand held flags held in various positions relative to the communicator’s body. The flags used are the same, ie flag OSCAR (flag diagonally split by the colours red and yellow. This form of communicating is virtually obsolete today but it may…
Introduction. Communication plays a very important part in modern society. We have advanced from the days of the old land-line based telephone and postal (snail) mail to mobile phones and e-mail. Technology has given us the ability to communicate with each other instantly and anywhere in the world. It has…
Air masses are large areas of air having the same characteristics throughout. They may be either warm or cold, depending on whether their source is polar or tropical. They are also classified as either maritime or continental. When two different air masses meet they form a boundary which is known…
Atmospheric pressure and temperature are mainly responsible for our weather systems. Atmospheric pressure is the pressure that the air exerts on the surface of the earth and everything on it. It changes with altitude and temperature. The air pressure in Johannesburg is less than that at the coast. When the…
If the cooling process which gives rise to cloud formation is continued, the droplets of which the cloud consists grow in size until they become too heavy to remain suspended in the air and they fall to the ground as rain. The longer the droplets are held aloft by the…
The formation of fog and mist is basically the same as that of clouds. In cloud the resulting condensation into visible particles takes place high above the ground, but for fog or mist, the condensation takes place on the surface of the sea or ground. The only difference between fog…
Clouds are formed when warm, moist air rises until it reaches the air’s saturation point (dew point). After this the moisture in the air condenses into visible droplets and clouds are formed. There are two basic types of cloud. Cumulus clouds. When air is heated by the surface of the…
The amount of water vapour in the air varies from place to place and from time to time, and is an important factor in determining the nature of the weather. The amount of water vapour that the air can hold in an invisible state is limited and varies with the…
The atmosphere is divided up into a number of layers as follows: The Troposphere. This layer stretches from the surface of the earth up to 18 kilometers above the earth. Most of the weather changes occur in this layer. Stratosphere. This layer stretches from 18 to 32 kilometers above the…
The met instruments usually carried aboard merchant vessels and warships are the following: Barometer. This instrument measures the atmospheric pressure (usually in millibars). They can either be mercury barometers or aneroid barometers. The first type uses a column of mercury to measure to measure the pressure, whilst the aneroid uses…
Sources of meteorological information available to the mariner include the following: Maritime coastal radio stations (Walvis Bay, Luderitz, Cape Town, Port Elizabeth, East London, Durban). These provide storm warnings and weather forecasts. Cape Naval Radio (Silvermine, Cape Town). They provide facsimile weather maps and weather forecasts on behalf of the…
Tugs are in effect marine tractors. Their purpose is to push/tow vessels when they cannot use their own engines or do not have any form of self propulsion. They are designed according to the environment in which they will operate, ie harbours, rivers or deep sea and according to their…
Dredgers come in a variety of forms, types and sizes. Their purpose is to remove silt or sand from harbours, rivers or entrance channels to harbours, in order that seagoing vessels have sufficient depth to navigate safely in these confined spaces. They are also used in underwater mining operations. Whilst…
There are a variety of fishing vessels which include trawlers, long-line craft, trap fishing craft, seiners, etc. Each has a different method of catching fish and is equipped accordingly. The seiner is a type of fishing vessel that uses sein nets to trap fish near the surface of the sea.…
Heavy lift vessels can be divided into two types, ie semi-submersible and conventional heavy lift vessels. The semi-submersible ships can lower their main cargo deck below the water line and large floating objects such as oil drilling rigs or damaged ships can be floated on or off the vessel. The…
The reefer or refrigerated cargo carrier is basically a general cargo vessel with well insulated holds. The cargoes carried are those requiring refrigeration, ie fruit, vegetables, meat, fish, etc. The cargo is usually packaged in boxes and palletted. It has small hatches, its own cargo handling gear and is fast.…
There are basically two types of liquefied gas carrier: One to carry natural gas such as butane (LNG – liquefied natural gas). LNG is carried by reducing the temperature to -160° C when it is carried in fast well insulated and expensive ships or by converting it (expensive process) into…
More than half the cargo carried by sea is oil carried in tankers. Since an oil cargo can be pumped on and off a tanker at a much higher rate than dry cargoes, tankers spend less time in port and in the space of one year can carry more cargo…
A bulk carrier is a large single deck ship, which carriers unpackaged cargo. The cargo is simply poured, tipped or pumped into the holds or tanks of the ship. The dry bulk carrier has been one of the largest growing types of ship outside the tanker fleets. The main cargoes…
Ro-Ro ships include car ferries, specialist vehicle carriers and general cargo vessels having Ro-Ro capabilities. They are expensive to build (a 15 000 dwt size costs twice the price of a conventional ship of the same size) and there is a considerable amount of wasted space, but their productivity is…
The concept behind containerisation is the packing of cargo into uniformly sized boxes (containers) and then designing all carrying vehicles (road, rail and ship)for the swift and efficient transport of these “boxes”, ideally from “door to door”. In order to make this feasible, it was necessary that an internationally accepted…
General cargo ships have not changed very much in the past 50 to 60 years. They remain multi-deck vessels of between 6 and 15 000 tons and are capable of loading dry cargo in either packaged or bulk form. Except that the superstructure has been moved aft, there is little…
Before World War 2, the main means of international passenger travel was by sea. It was also the main means of getting post (letters, documents, parcels, etc) from one continent to another. Hence the name “mail ship”. After the war, with the rapid development of aircraft, sea travel was replaced…
Introduction. There are many different types and class of vessels that make use of South African ports, ie naval vessels, fishing craft, trawlers, dredgers, cable layers/repair vessels, ocean research vessels, tugs, etc. In this section however, we will be looking at the commercial types only – namely: Passenger ships. General…
Since the very beginning of man’s ventures upon the high seas there have been disasters at sea. Some were caused by nature but many more have been caused by man himself. The seabed around our coast is littered with wrecks dating back to the early Portuguese explorers. Besides the loss…
A shipboard fire is another nightmare for seamen. Unfortunately there is no fire department to call upon and you cannot evacuate the crew. This means that the crew themselves have to combat the fire and put it out. This means that the entire ship’s company, irrespective of whether he is…
Introduction. Emergencies usually occur when they are least expected and usually under less than ideal conditions. This is particularly true when they occur at sea. Because of this, ships usually make provision by having standard drills and by practising them regularly. The idea is that by doing the drills often…
Normally these days most vessels have auto-pilots (a computer steers the ship) but when it breaks down and also when entering and leaving harbour and navigating in restricted waters, the ship has to be steered manually. At sea most English speaking maritime countries use a common form of wheel orders…
Since a ship operates 24 hours around the clock, the crew is divided into watches. This applies to both the deck department and engineering. What are the watch keepers responsible for? Responsibilities. The watch keepers are responsible for the following during their period on watch: Ensuring the effective and efficient…
The line is brought in around the after of the bitts and then figure of eight turns are taken between the two bitts. The last turn should be a locking turn. If the vessel is being tied up for a length of time, then the lines should be lashed down…
The following two sketches show the terms and elements used with bends and hitches: Reef knot. A reef knot consists of two overhand knots made consecutively. It is used as a common tie for bending together two ropes of equal size. It is not liable to become undone when there…
Before a rope is used one should always ensure that the ends are whipped. This prevents the ends from turning into “horses tails” and starting to unravel. It also makes the rope more seamanlike and neater. A whipping should always be at least equal in length to the diameter of…
The following should be born in mind when handling mooring lines/ropes: Be constantly aware of what is happening around you. Never sit on the bulwark or railing while waiting for something to happen. When throwing a heaving line, never stand on the edge of the deck. When waiting to send…
When working with ropes the following should be borne in mind at all times: Never lead a rope around a sharp bend or over an edge. The chaffing action will quickly wear away the rope and cause it to part. To minimise this, always lead the rope around a smooth,…
There are five types of synthetic ropes, namely Nylon (Polymide). Nylon is the strongest of all ropes in common use and is slightly stronger than polyester. However, if it is much used, it becomes weaker than polyester. It is also the most elastic of all ropes and can stretch up…
There are five types of natural rope, namely the following: Manila. Manila is a golden brown colour and is made up of strands from a type of banana plant (the abaca) which grows in the Philippines, Borneo and central America. When mature the abaca plant grows to a height of…
The collective term used for all types of rope, twine and lines is cordage. Unlike the past when rope was measured by its circumference, it is now measured across its diameter. It is made either from vegetable or man-made fibres. The fibres are twisted together to form yarns, which are…
At sea a ship requires personnel to operate it on a continuous basis. In order to do this the crew have to work shifts or watches. The system of watchkeeping may differ from ship to ship, but the system usually employed is based upon a three watch rotation, ie four…
The deck department comprises all the navigating officers and seaman ratings carried onboard. Their duties and responsibilities are as follows: Navigating officers. They are responsible for the “driving” of the vessel. By this is meant: The safe navigation of the vessel. Managing the day to day running of the vessel.…
There are considerable differences between the organisation of naval and merchant ships and yet there are also basic similarities. In this module we will be looking at the merchant navy structure. The master of a ship is usually referred to as the captain which is usually the rank of the…
Hull plating. The outer surfaces of the hull is built of steel plates that are welded together and to the main internal structural members of the hull. The plates are welded end to end to form a panel of plating which runs forward and aft and is known as a…
Water-borne vessels are constructed of various materials, ie steel, aluminium, wood, glass reinforced plastics (GRP). Steel is used for large vessels. Aluminium is used for very small craft and for on-board structures, ie minor bulkheads, deck houses, guardrail and awning stanchions, non-watertight doors and furniture. Wood is used for pleasure…
Dry dock (graving dock). This is an excavation faced with solid masonry which is connected with a harbour, river or basin. The entrance is closed with a sliding caisson, a floating caisson or dock gates. Water is admitted through special valves until the level of the water in the dock…
Miscellaneous ship terms. The following are nautical terms used for various ship’s fittings and structures: Deck head. This is a ceiling in a ship. Bulkhead. This is a wall in a ship. Hatch. This is an opening in a deck to allow vertical access between decks. These can be small…
The Hull. This is the main part of the ship. It is divided into three sections, namely the fore part, the midships part and the after part. The fore part ends in the stem, which is the leading edge of the hull. The after part ends in the stern, which…
Although there are many natural hazards that confront man on land, being a land-based creature, his natural instincts allow him to cope with them most of the time. At sea the situation is different. It is not man’s natural habitat or environment and he has to learn new skills in…
Nautical Almanac. The data recorded in the nautical almanac is usually recorded against UT (universal time or GMT). This is for convenience sake and when looking up any of the information one has to convert the zone time to GMT. In the case of the predicted times of sunrise, sunset,…
Zone designations. A ship’s clocks will not necessarily be altered the moment she enters a new zone. The fact that she is crossing a dividing meridian and entering a new zone does not alter the time she is keeping. Her clocks are altered to suit the convenience of those onboard.…
Standard time on land. The boundaries of time zones on land generally agree with that at sea, which are defined by the meridians 7½°, 22½°, etc, except when modified as necessary by the territorial limits of the countries concerned. Zone time on land is referred to as standard time. For…
A uniform time keeping system has been adopted for use at sea to ensure that all vessels within certain defined limits of longitude keep the same time. The world has been divided longitudinally into 24 zones of 15° each with the system centred on the meridian of Greenwich. The centre…
Introduction. Because of the international nature of sea travel where vessels traverse large distances, especially in east/west directions, time is a very important aspect of the mariner’s life. For convenience sake a “24 hour clock” is used. This means that by merely looking at the time will indicate whether forenoon…
Problem: Your vessel is anchored approximately 2 miles west of Cape Light. A horizontal sextant angle between the following points was taken: Cape Light and the water tower south of the light = 65° At the same time a vertical sextant angle was taken of Cape Light. The sextant reading…
Vertical danger angle. A vertical sextant angle can be used to ensure the safety of a ship in the vicinity of dangers. If the danger is close to high land or a lighthouse, the height of the land or lighthouse can be used as a reference for determining the sextant…
A position circle can be obtained from the rising or dipping of navigation lights over the horizon. The South African List of Lights and Radio Signals has a table of geographical ranges of lights. By entering the table with the height of the observer’s eye above water level and the…
Leading lights and markers are usually used in the approaches to harbours or in channels where maneuvering room is very restricted. Their purpose is to guide vessels clear of dangers or down the best channel. They are shown on the chart by a line drawn through them called a leading…
The GPS will provide a position expressed in latitude and longitude. This will be plotted as a small cross, the centre of which is encircled, with GPS written alongside it.
If an observer sees two object in line ashore, ie beacons, then he must lie somewhere on the extended line joining them. This provides an excellent position line, provided the distance between the observer and the nearer of the two objects is no more than three times the distance between…
Using a sextant, an angle can be measured between two objects ashore, the position of which is known. By plotting the intersection of two lines forming the horizontal sextant angles between the two objects, a circular position line can be drawn. Remember that all angles subtended by a chord in…
Using a sextant, a distance may be obtained of a vertical object of known height, by measuring the angle subtended by the object at the eye of the observer. The determination of the distance is then merely a problem of solving a right angled triangle. One can either do this…
A fix may be obtained by using the range of objects ashore, the position of which is known from the ship. The range may be obtained from various sources, ie vertical sextant angle of an object, the height of which is known, range-finder or distance meter, a horizontal sextant angle…
Radio direction finding (DF) bearings. Use may be made of radio transmissions to obtain a position line. It would necessitate either the ship having a radio direction finding capability or asking a shore radio station that is equipped to take DF bearings to take a bearing of the ship’s transmissions.…
Cocked hat. When three or more bearings are taken from a moving ship, the resulting position lines will not as a rule meet in a point, but form a triangle. This triangle is known as a cocked hat. The name “cocked hat” probably refers to the type of hat worn…
Taking bearings. Bearings are taken using the azimuth circle fitted to the compass repeater. It is specially designed so that you can observe the object through a metal sighting V on top of a glass prism and the graduations on the compass card through the glass prism at the same…
Ship’s track. The ship’s course line or “track” is a straight line drawn on a chart in the direction of it’s course. It has arrow heads pointing in the direction of the course and the course is written in along the track. The speed of the vessel is written in…
The observed position. The position obtained by the intersection of two or more position lines obtained from the observation of heavenly bodies is known as the observed position. It is shown on the chart as a dot surrounded by a circle, with “Obs” and the time written next to it.…
The ultimate goal of the navigator’s activities is to produce a record of his voyage, be it either in the form of a paper or digital chart. This includes the planning and execution of the voyage and the monitoring thereof. Because of the international nature of sea voyages and the…
Compass bearings The angle between the direction of a place or object and compass north is called the compass bearing. As previously stated it is distinguished by the suffix (C) after the bearing. Like true and magnetic bearings it is written in three figure notation. In order to change a…
Variation Variation is defined as the angle between the true and magnetic meridians. It is said to be easterly if the direction of magnetic north lies to the east of the true meridian and westerly if it lies to the west. Variation can b e obtained from a special isogonic…
Bearings can also be expressed in relative terms, ie bearings relative to the ship’s fore and aft centreline. All bearings on the port side will be prefaced with the word “red” and those to starboard, with the word “green”. They will be followed by the angle measured from the bow,…
In the days of sail it was virtually impossible to steer a course accurately to within a degree. As a result the compass was divided into thirty two equal “points”, each 11¼° wide. The four major points, namely north, south, east and west, are referred to as the four cardinal…
Three figure notation. All bearings and headings (courses) are expressed in three figures. For example: North is expressed as 000°. South is expressed as 180°. North-west is expressed as 045°. Five degrees to the right of north is expressed as 005°. The reason for this is to avoid confusion with…
So far we have covered the basic definitions and concepts used in nautical navigation. We will now look at a number of simple problems to demonstrate our understanding of these definitions/concepts. This practical assignment assumes that you have access to a physical copy of a nautical chart for the Table…
Need for Passage Planning. Just as you would not make a long journey by car without proper planning beforehand, so is it with sea voyages. In fact it is even more essential. Remember there are no roads at sea and the surface of the sea is not smooth and static.…
Navigational charts are produced by the Hydrographic authorities of a country. In our case the authority is the SA Navy Hydrographic Office. The headquarters of the hydrographer is situated at Silvermine in Cape Town. The charts are compiled and printed according to international standards and conventions and are therefore usable…
East and West. The earth is a sphere which rotates about its own axis. The direction towards which it rotates is “East” and the opposite direction is “West”. See the sketch below. North and South. The axis of the earth has two poles. The pole to one’s left when facing…
Besides the navigation equipment used by the navigator, the latter also requires certain instruments, publications and stationery to assist him in the performance of his duties. The items include the following: Charts. Just as you would require roadmaps to plan and monitor your holiday, so does the navigator when planning…
Though the number and types of navigation equipment may differ from ship to ship, virtually all ships will carry the following: At least one gyro compass (the primary compass). A magnetic compass (the auxiliary back-up compass). At least one radar (operating in the 30 GHz frequency band). Ideally it should…
Although all deck officers are navigators it is usually the practice to appoint one of the officers as “the navigator” who is responsible for planning and overseeing the navigation function aboard a seagoing vessel. Broadly, his duties/responsibilities are the following: The preparation and planning of the safest and most economical…
Navigation can be defined as the process followed in getting a vessel from one geographical point to another in the safest and most economical way. Whilst the methods used are based upon sound scientific and mathematical principles, their efficient execution is based upon the experience and skill of the navigator.…
This website has been compiled for the guidance of and use by grade 10 learners taking Nautical Science as one of their secondary school subjects. It follows the approved national curriculum for the subject and comprises four parts, namely Navigation, Seamanship, Meteorology and Communications. Although it has been written for…
When using a radio one should bear the following in mind: Unlike your telephone it is not a private circuit. Anyone who has a radio covering the same frequency can listen in. There may be many users waiting to use the same circuit. Your use of the radio must be…
The use of the safety signal implies that the station making the call has an important navigational or meteorological warning to transmit. All stations hearing the safety signal shall listen to the safety message until they are satisfied that the message is of no concern to them. It should take…
An urgency message indicates that the station making it has a very urgent message to transmit concerning the safety of the mobile unit or person. It is only sent on the authority of the master or person responsible for the ship. The urgency signal will have priority over all other…
A distress call and message is sent when a vessel is in grave and imminent danger. They are only sent on the authority of the master or person responsible for the vessel. A distress call has priority over all other transmissions. All stations receiving a distress call and message must…
Distress frequencies. For the purposes of safety and distress there are certain frequencies that have been specially reserved for their exclusive use internationally. They are the following: Medium frequency (MF) 518 kHz. Used by coast radio stations to transmit meteorological and navigation warnings and urgent information to ships using the…
General. Technology has changed the way we communicate at sea quite considerably. In grade 12 you will be introduced to the Global Maritime Distress and Safety System (GMDSS) but during grade 11 we will be discussing distress and safety communications outside of the new automated system. The old system relied…
Types of current. Unlike tidal currents, ocean currents are not dependent on gravitational effect produced by the interaction of sun and moon. They are caused by the differences in level, or in salinity/density, or in temperature between various masses of water, in which case they are called stream currents, or…
Nature. Tropical storms are violent storms with very strong winds and heavy seas. Origin. They occur mostly in the late summer and early autumn (December to April in the southern hemisphere). They originate in the tropics between latitude 5° and latitude 10° north or south and develop only over the…
Life Cycle of a frontal depression. Warm air moves faster than cold and every now and again, it forces its way into the cold air, making a bulge in the polar front. This is the commencement of a frontal depression, since as the warm, less dense air pushes into the…
Air masses are large areas of air which have the same characteristics throughout. They may be warm or cold, depending upon where they originated, ie tropical or polar. They are further classified as either continental or maritime. When two different air masses meet they form a boundary which is known…
Last year we spoke about two atmospheric pressure systems, namely the Depression and the Anti-cyclone. This year we continue with systems which are basically derivatives of the first two: High pressure ridges. They are also known as “wedges”. It is an extension of an anti-cyclone and it could extend in…
The oceanic winds experienced in the various climate zones are described in the following sub paragraphs: Doldrums. The doldrums is that part of the ocean situated in the equatorial trough of low pressure between the trade winds of the two hemispheres. This weather in this zone is characterised by calms,…
The planetary wind circulation for the “ideal” earth which would be covered with water is shown in the following sketch:
Last year we had a look at the causes and elements of weather. This year we will be looking at the various weather systems and the weather the mariner can expect from them. We will also be covering tropical storms, the danger they pose and the action the mariner can…
The towing mentioned in this section, refers to the towing of one vessel by another in an emergency and not the professional towing of a vessel by a tug/salvage vessel. All vessels usually have a dedicated towrope/wire which is specially made up for use during an emergency. Depending on the…
A fire onboard poses a very serious threat to the vessel and the crew. There is no municipal fire service to call upon and there is no escape from the consequences of the fire. For this reason it is imperative that every precaution is taken to prevent a fire from…
Collisions. When ships are about to collide, the following action should be carried out: When one ship collides with another, there is greater likelihood of loss of life and serious damage if one vessel strikes another in the midships position where the compartments are larger (ie engine room). Every attempt…
When it seems that the ship will have to be abandoned, the following action must be taken: The lifeboats and life rafts must be prepared for launching. In remote areas where the likelihood of an early rescue is small, consideration should be given to placing more blankets and provisions in…
All ocean-going vessels are required to carry twelve parachute flares, the characteristics of which are the following: The rockets must reach a height of at least 300 metres when launched vertically. The parachute flare must burn with a bright red colour. It must burn for at least 40 seconds. It…
When a vessel is in danger of sinking, lifeboats and rafts are not always available for abandoning ship. In such cases the crew and passengers should, if possible, remain on the ship until another vessel arrives on the scene and sends boats or rafts across. The rescue should not be…
If a vessel is disabled or in distress the following actions should be considered: If it is disabled and the safety of the crew and vessel is not an immediate issue. Hoist/activate the not under command shapes or lights. Try and repair the vessel. If the crew cannot repair the…
When a sea boat is launched to recover survivors and the sea is rough, then the following should be done to limit the damage and risk to persons in the boat: The rescue ship should stop upwind of the area to provide a sheltered lee for the sea boat to…
If a person falls overboard whilst the vessel is under way, the following procedure should be carried out: A lifebuoy fitted with a self-acting light/smoke generator should be launched over the same side as the person fell. The helm must be put hard over to the side the man fell.…
Whilst the rescue vessel(s) are steaming towards the casualty area, the crew should start preparing for the rescue of the survivors. Whilst it is difficult to envisage every possible action one could take, the following should be considered when drawing up the plan. The weather and sea state in the…
It is of great importance that all rescue operations are properly coordinated and with the new Global Maritime Distress and Safety System (GMDSS), the prime responsibility for coordination falls on the shoulders of shore base authorities, ie the Rescue Coordination Centre (RCC). At sea the ship with the best communications…
One can stop a vessel by one of the following methods: Inertia stop. Stopping the engine(s) and coasting to a standstill with the friction of sea and air overcoming the ship’s inertia. The total distance run will depend on the type of vessel, the initial speed, the displacement, the trim…
Factors affecting the acceleration / deceleration of a vessel Before discussing methods of stopping a vessel, we should look at the factors that affect the acceleration and deceleration of a vessel . They are the following: Inertia. Here we are talking about the amount of energy required to move an…
Definition. A newly discovered hazard to navigation not yet shown on the charts or included in sailing directions, nor sufficiently promulgated by notices to mariners, is termed a New Danger. The term covers naturally occurring obstructions such as sandbanks, or rocks or man-made dangers such as wrecks. Marking. Cardinal or…
Purpose. To indicate to the mariner a special area or feature the nature of which is apparent from reference to a chart, sailing directions or notices to mariners. Special marks may be lettered to indicate their purpose. Uses include the following: ODAS (Ocean Data Acquisition System) buoys. Traffic separation schemes…
Purpose. Safe water marks are used to indicate that there is navigable water all round the mark. It could be used as a centre line, mid-channel or land fall buoy, or to indicate the best point of passage under a bridge. Colours. Red with white vertical stripes are used for…
Purpose. Isolated danger marks are erected on or moored on or above isolated dangers of limited extent which have navigable water all round them. On Admiralty charts the position of the danger is the centre of the symbol or sounding indicating the danger. Top mark. Black double sphere top marks…
Cardinal marks are used together with the compass to indicate where the mariner may find the best navigable water. They are placed in one of the four quadrants (North, south, east or west), boundered by inter-cardinal bearings. The mariner is safe if he passes north of a North cardinal mark,…
Purpose. Lateral marks are used for well defined channels in conjunction with the general direction of buoyage. They indicate the port and starboard hand sides of the route to be followed. Direction of buoyage. The conventional direction of buoyage is defined in one of two ways: Local direction of buoyage.…
Application and purpose. The system applies to all fixed and floating marks, other than lighthouses, sectors of lights, leading lights and marks, lanbys, certain large light floats and light vessels. Its purpose is to indicate: The sides and centrelines of navigable channels; Navigable channels under fixed bridges; Natural dangers and…
The boundaries of the two buoyage regions A and B in which the colours of the lateral marks and their lights are reversed, are shown in the following diagram:
Up till approximately 128 years ago there was no uniform system of buoyage among maritime nations. This was an unacceptable situation and in 1889 a number of countries got together and decided to do something about it. They agreed to mark the port side of channels with black can buoys…
RULE 37: Distress Signals When a vessel is in distress and requires assistance she shall use or exhibit the signals described in Annexure IV to these regulations. Annexure IV – Distress signals Need of Assistance: The following signals, used or exhibited either together or separately, indicate distress and need of…
Rule 32: Definitions The word “whistle” means any sound signalling appliance capable of producing the prescribed blasts and which complies with the specifications in annex III to these regulations. Note: the annex is not included in these notes. The grade 11 and 12 learners are not required to know these…
RULE 20: Application Rules in this part shall be complied with in all weathers. The rules concerning lights shall be complied with from sunset to sunrise, and during such times no other lights shall be exhibited, except such lights as cannot be mistaken for the lights specified in these rules…
RULE 19: Conduct of Vessels in Restricted Visibility This rule applies to vessels not in sight of one another when navigating in or near an area of restricted visibility. Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and condition of restricted visibility. A power driven…
RULE 11: Application Rules in this section apply to all vessels in sight of one another. RULE 12: Sailing vessels When two sailing vessels are approaching one another, so as to involve risk of collision. One of them shall keep out of the way of the other as follow: when…
SECTION I – CONDUCT OF VESSELS IN ANY CONDITION OF VISIBILITY RULE 4 : Application. Rules in this section apply to any condition of visibility. RULE 5: Look-out. Every vessel shall at all times maintain a proper look-out by sight as well by hearing as well as by all available…
RULE 1 – Application The abovementioned rules shall apply to all vessels upon the high seas and in all waterways connected therewith, navigable by seagoing vessels. Appropriate authorities may make special rules for harbours, roadsteads, rivers, lakes or inland waterways connected with the high seas and navigable by seagoing vessels,…
All of the above tackles/purchases are designed to increase the power utilised to the effect achieved. Because of friction between the ropes and sheaves, the actual (theoretical) weight lifted can be roughly calculated as being: Weight + (1/10 x weight) for each sheave. The mechanical advantage gained can be found…
Purchase. A purchase is a combination of blocks or pulleys rove with a rope, wire or chain. Tackle. A tackle is a purchase consisting of a rope rove and through two or more blocks, in such a way that any pull applied to the hauling part, is increased by an…
In order to lift heavier weights, a system of blocks and tackles was gradually introduced. Originally they were made out of wood, but as the loads got heavier and they had to withstand harder work they were made out of steel. It is very rare these days to find a…
Cargo working gear consists of shackles, cranes, derricks and their associated equipment, masts and Sampson posts and the wires/ropes used to connect them all together. Shackles. Types: Shackles are named according to their different shapes, ie “D” or “Straight backed”, “Bow” or “Harp” shackles. One other type which is not…
Until now we have been looking at the loading and discharge of what is known as General Cargo. There has been a large shift away from general cargo vessels with the introduction of containers. Containers are very large steel boxes with lockable doors at one end. Thr idea is that…
The loading and discharging of cargo is greatly eased with the help of the proper equipment for its handling. In this chapter we will be discussing the various items of equipment and their uses. Rope slings. Rope slings are constructed by joining the ends of a piece of 25 to…
Whilst currents/tidal streams have the greatest effect on the movement of vessels, the wind can also affect their movement. The effect of the wind on vessel movement is two fold: Firstly, it will cause an increase or decrease of the speed through the water depending on whether the wind is…
The following example is used to explain the procedure to follow: Problem: A vessel steaming at 10 knots wishes to make good a course of 110° (T) from its 1200 position. Find the course to steer allowing for a current setting 170° (T) at 2 knots. Solution: Plot the 1200…
The following example is used to explain the procedure to follow: Problem: From an observed position at 1200 a vessel steers 110° (T) at 10 knots. The current is setting 350° (T) at 2 knots. Determine the estimated position for 1330. Solution: Plot the true course from the 1200 position.…
The best way of demonstrating how to find the set, rate and drift of a current is by using a practical example: Problem: From an observed position at 1200 a vessel steers 110° (T) at 12 knots. At 1330 another fix is obtained. Determine the set rate and drift of…
When plotting courses of vessels and the set of a current/tidal stream, the direction of travel is indicated by arrow heads pointing in the direction of travel. The number of arrow heads differentiate between courses steered, courses made good and the set of a current/tidal stream: One arrow head =…
The following terminology is used with currents and tidal streams: Set – we speak about the set of the current/tidal stream when referring to its direction of flow. It is expressed in degrees (°). Rate – this is the speed of the current/tidal stream expressed in knots. Drift – this…
Nature of currents. Currents are permanent or seasonal horizontal movement of water flowing in a certain direction and in the oceans caused by differences in temperature, salinity, density and wind. Information concerning their direction and strength is given on charts, in Sailing Directions and various current atlases. The net result…
The tide tables are used to determine the heights and times of high and low water at all the major ports in Namibia and South Africa. They are also used to determine the height of tide at anytime during the year at these ports. When using the tables certain parameters…
Highest Astronomical Tide (HAT) and Lowest Astronomical Tide (LAT). These levels are predicted to occur under average meteorological conditions and under any combination of astronomical conditions. They will not be reached every year. They are also not the extreme levels that can be reached, as storm surges and other meteorological…
The Hydrographer of the SA Navy is responsible for producing a table of tides covering the South African coast and that of Namibia. These tables contain: The predicted times and heights of low water and high water in all South African and Namibian ports, as well as the phases of…
Tides can be defined as the periodic rise and fall of the level of the sea caused by the combined solar and lunar gravitational forces acting on the earth. There are generally two high waters and two low waters occurring at any place during a period of 24 hours and…
The procedure laid out below should be followed to find the latitude of the observer at meridian passage. A pro forma format for working the problem out is also provided and should be followed in conjunction with the procedure. A good navigator will start preparing for the midday sight an…
When the sun and the observer’s zenith are on the same celestial meridian, then there is a simple relationship between declination, zenith distance and the latitude. All three are arcs of the same great circle and their values give the distance of each point from the celestial equator (equinoctial) and…
The local mean time (LMT) of mer pass on any meridian is obtained from the Nautical Almanac. At the bottom of the right hand page of the three-daily tables is a small table entitled “sun-mer pass”. The time of mer pass for the three days covered by the page is…
Introduction Meridian passage of an observed heavenly body, ie the sun, occurs when the body is directly over the observer’s meridian and the local hour angle (LHA) is zero. During this course we will only be covering the meridian passage (mer pass) of the sun. Those who wish to become…
Total correction tables. The altitude correction tables for the sun are given at the beginning of the Nautical Almanac. They cover all altitudes from 0° to 90° and the heights of eye from 1 to 48 metres. The tables provide corrections to apply to both the upper and lower limbs…
Because of their relative sizes and nearness to the earth, the sun and moon are not merely seen as points of light but as spheres with sizeable diameters. Therefore, in order to take a sextant altitude, the observer needs to measure the angle between the horizon and their upper or…
When a ray of light passes at an angle from a less dense medium to a higher density medium, it is bent towards the normal (an imaginary line running at right angles to the surface between the mediums). This is referred to as refraction. The visible light from a heavenly…
This is the angular difference between the altitude measured between the apparent horizon and the body as seen through the observer’s eye and the altitude which would be measured between the body and the horizon as seen from the surface of the sea. The observer will always be a certain…
Sextant altitude, observed altitude and index error. The altitude is measured by a sextant and although they are precision instruments, there is always a slight difference between the sextant altitude and the observed altitude caused by the design and manufacture of the instrument. This difference is referred to as the…
When we take a sextant altitude of a heavenly body, we measure the angle between the body and the visible sea horizon as witnessed from the observer’s position on the bridge of a vessel. (angle DOX in the diagram). This is referred to as the observed altitude. In converting it…
Individual corrections. In order to be able to use the altitude obtained by sextant of a heavenly body, we need to convert it from a sextant altitude to a true altitude. To do this we need to apply five individual corrections to the altitude obtained from the sextant, namely corrections…
Adjustment screws. Every sextant is equipped with error adjustment screws. The design of these screws varies from sextant to sextant. Some have ordinary screw driver slots while others have round heads with a hole drilled through it. The first requires the use of a suitable screw driver whilst the others…
Reading the sextant is very simple: Degrees are read directly from the graduated arc opposite the index mark on the index arm. Minutes are read from the micrometer drum opposite the vernier index mark. Seconds are read from the vernier where one of the vernier graduations lines up with one…
Before housing the sextant in its case, set the index arm to the middle of the graduated arc and turn all the shades inwards (ie towards the centre of the instrument). Place the sextant carefully in the box ensuring that the three legs at the rear of the instrument enter…
Depending on type and manufacturer, the sextant case will either be made of a hardwood or plastic. The wooden cases are fitted with a carrying handle, patent fasteners, lock and key. Inside the case are wooden chocks built to prevent the sextant being dislodged. The plastic case does not have…
The sextant is made up of the following parts: The frame. The handle. The telescope or monocle. The rising piece. The arc. The index arm. The clamp. The worm and rack. The micrometer drum. The micrometervernier. Electric light. The index mirror. The index mirror clips. The index mirror (first) adjustment…
Although the marine sextant is seldom used these days due to the introduction of satellite navigation systems (ie GPS), it still can be used for the following: Measuring the altitude of the stars, sun, moon and planets in order to determine geographical position out of sight of land (ocean navigation).…
Introduction. The marine sextant is a precision built optical instrument f which is used to measure altitudes and angles. It used to be an essential part of a ship’s navigation equipment. The sextant got its name from the fact that the length of its graduated arc is approximately one sixth…
Explanation of twilight. Twilight is the period of approximately one hour’s duration before the sun rises in the morning and the period of approximately one hour’s duration after the sun sets in the evening, ie between the times when the sun is 12° below the horizon and sunrise in the…
Calculating times of sunrise and sunset. The times of the visible rising and setting of the sun are contained in the daily pages of the nautical almanac. They are tabulated for the middle day of the three on that page and provide the Local Mean Time (LMT) of the rising/setting…
Polar Distance. This is the angular distance of a body from the elevated pole (the pole that is above the celestial horizon). This is the distance PX in the sketch. When the elevated pole and the declination have the same names, the polar distance is 90° – declination. When they…
Since the declination gives us the “latitude” of the heavenly body we must now find it’s “longitude”. We do this by measuring the angle between the celestial meridian passing through the body and that running through the observer’s position. The hour angle is defined as “the angle between the meridian…
Declination. Declination corresponds to terrestrial latitude and is defined as the angular distance of a heavenly body north or south of the celestial equator, measured in units of arc (ie degrees, minutes and seconds). Declination is the result of the earth’s movement/orbit around the sun and the fact that the…
Introduction. Astro-navigation is based upon the concept of the “celestial sphere”. What is the “celestial sphere”? If one looked up into the night sky one would see what would appear to be an enormous black dome with all the heavenly bodies stuck to the inside like thousands of diamonds. This…
Scale of a Mercator chart. Because the equator is shown on a Mercator chart as a straight line of definite length and the meridians appear as straight lines perpendicular to it, the longitude scale is fixed by that length and is constant in all latitudes. The latitude scale, on the…
‘Sailings’ is a term given to various methods used to determine courses and distances to be steamed when travelling from one geographical position to another. There are six different “sailings”, ie Parallel, Plane, Middle Latitude, Mercator, Great Circle and a combination of Great Circle and one of the others. During…
This website has been compiled for the guidance of and use by grade 11 learners taking Nautical Science as one of their secondary school subjects. It follows the approved national curriculum for the subject and comprises four parts, namely Navigation, Seamanship, Meteorology and Communications. Although it has been written for…
By parallel sailing we mean travelling along a parallel of latitude from one place to another. This means that one would either be travelling directly westward or eastward [270° (T) or 090° (T)]. The distance along a parallel of latitude between two particular meridians decreases as the meridians converge towards…
When we refer to plane sailing we mean sailing from one position to another where the latitude and longitude of each is different to the other. Because we are using a mean latitude, this method is not very accurate over long distances and should be confined to distances of 600…
