this is my study note

1. Hafez Ahmad Department of Oceanography, University of Chittagong
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Seamanship and maritime navigation [411]
Seamanship: Seamanship is an art or qualities possessed by the seafarers to operate the ships safely at sea.
Seamanship is evolutionary and dynamic in nature. Why is it Evolutionary in Nature?
Seamanship is not something that can be mastered in schools, rather it is an experience. It is acquired over
some time. We are taught various things about seamanship in training institutes which indeed helps in
establishing the foundations but real acquisition starts onboard ships only. I would like to supplement this
fact with an example. You cannot ask a Seaman on the first day who is first on board for making a bowline
on a rope or handle the ropes alone while in the station. However, he knows bowline because it has been
taught in a training institute to him. But he needs some time to get accustomed to the real environment and
to gain real experience which is different from the training institute. After some months with the experience,
he would be able to handle the situation alone. Because he has acquired art over some time. Thus, it is
evolutionary (Gradual Learning).
Why is it dynamic?
Seamanship is a very vast subject. It is not a fixed set of qualities that every seaman possesses, rather it
varies from seaman to seaman. For example, as a navigational officer, I cannot expect the Able Seaman
(AB) to take the navigational fix for me. Because this is certainly not his qualities. He is expected to operate
the helm of the ship. Whereas I was an in-charge of the navigational watch must know the operation of all
Navigational equipment as well as operation of helm too. Therefore it varies from seaman to seaman. You
can look at dynamism with the Individualistic aspect too. Previously I was working with paper charts and
accustomed to it. But with the advent of technology, Electronic Charts have evolved. Now I have to upgrade
the qualities by learning to operate electronic charts. Otherwise, I am not fit to serve the sea, Hence
Seamanship qualities are not static, and rather they are dynamic.
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of
a craft or vehicle from one place to another. The field of navigation includes four general categories:
a. land navigation,
b. marine navigation,
c. aeronautic navigation,
d. Space navigation.
Navigation, describe commonly used navigation types / methods?
Navigation can be divided into four basic types. They are,
1. Piloting: Piloting may be defined as the determination of the position and the direction of the
movements of a vessel involving frequent or continuous reference to landmarks, aids to navigation
and depth soundings. Piloting is done only in coastal water where we have a sight on land. Piloting
normally provides a vessel’s position with precision and accuracy.
2. Dead reckoning (DR) : Dead Reckoning (DR) is one of the four main divisions of navigation. When
the earliest mariners become sufficiently daring and skilled to venture beyond their known waters
in which they could pilot their vessel, they developed dead reckoning as a means of keeping track
of their position. Dead Reckoning is the process of determining a ship’s approximate position by
applying to its last well determined position a vector
3. Celestial navigation: Celestial navigation is the determination of position by observing the celestial
bodies such as the Sun, Moon, planets and stars, by drawing lines of position using tables, spherical

2. Hafez Ahmad Department of Oceanography, University of Chittagong
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trigonometry, and almanacs. It is used primarily as a backup to satellite and other electronic systems
in the open ocean.
4. Radio navigation: Radio navigation is the determination of position and to lesser extent, course
direction using information gained from radio waves received and processed on board a vessel or
aircraft. It uses radio waves to determine position by either radio direction finding systems or
hyperbolic systems. Radar navigation also uses radar to determine the distance from or bearing of
objects whose position is known, in addition to the collision avoidance system. Radar is ‘electronic
piloting’ and the use of satellites is a unique application of radio waves. Radio navigation system
in general provides coverage of a few hundred to many thousands of miles with accuracies from +
5 miles.
Describe for marine navigation: prime meridian, sailing direction/pilot, the log, nautical mile
the difference between "magnetic north" and "true north" is an angle that varies slightly from place to
place (and from year to year, because the position of Earth's magnetic north is constantly changing) and
it's called the declination or variation. When really accurate navigation is important (for example, on
ships), you have to take the declination into account and correct for it.
Marine navigation is The process of directing the movements of watercraft from one point to another; the
process, always present in some form when a vessel is under way and not drifting, varies with the type of
craft, its mission, and its area of operation.
A nautical mile is based on the circumference of the earth, and is equal to one minute of latitude. It is
slightly more than a statute (land measured) mile (1 nautical mile = 1.1508 statute miles ). Nautical
miles are used for charting and navigating.
Magnetic deviation often refers specifically to compass error caused by magnetized iron within a ship or
aircraft. The deviation errors caused by magnetism in the ship's structure are minimized by precisely
positioning small magnets and iron compensators close to the compass.
These are imaginary lines, which pass from pole to pole. In the charts (Mercator) these lines are drawn as
vertical lines and parallel to each other. The prime meridian which passes from pole to pole through the
site of the Royal observatory at Greenwich, England.
Important of studying seamanship in oceanography
Seamanship skills include safety at sea, maintenance, knot typing, hitching, splicing, ropes and wires,
mending of nets, cargo handling. A fundamental skill of professional seamanship is being able to maneuver
a vessel with accuracy and precision. Ship handling is about arriving and departing a berth and in proximity
to other ships, whilst at all times navigating safety. A key ability for a ship handler is an innate
understanding of how the wind, tide & swell, the passage of other vessel, as well as the shape of seabed,
will effect a vessel’s movement, which together with an understanding of a specific vessels performance,
should allow that vessel a safe passage.
Draw typical research vessel and different terms used for different parts and section in a research
vessel
A research vessel (RV or R/V) is a ship or boat designed, modified, or equipped to carry out research at
sea. A typical RV consists of following basic instruments
1. CTD: an oceanography instrument used to measure the conductivity, temperature, and pressure of
seawater

3. Hafez Ahmad Department of Oceanography, University of Chittagong
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2. coring / drilling 3. GPS 4. SONAR 5. RADAR 6. Autonomous underwater and unmanned vehicles
7. remotely operated vehicle 8. trawling /nets 9. onboard laboratory 10. cranes ,winch
Describe pilotage, way point and position fixing navigation
Waypoints are sets of coordinates that identify a point in physical space.
In position fixing navigation, a position fix (PF) or simply a fix is a position derived from measuring in
relation to external reference points. Usually, a fix is where two or more position lines intersect at any
given time.
Piloting or pilotage is navigating, using fixed points of reference on the sea or on land, usually with
reference to a nautical chart or aeronautical chart to obtain a fix of the position of the vessel or aircraft
with respect to a desired course or location.
Principal dimension: The principal dimensions of a ship are length between perpendiculars, beam,
draft, and depth

4. Hafez Ahmad Department of Oceanography, University of Chittagong
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1. After Perpendicular (AP): A perpendicular drawn to the waterline at the point where the aft side
of the rudder post meets the summer load line. Where no rudder post is fitted it is taken as the centre
line of the rudder stock.
2. Forward Perpendicular (FP): A perpendicular drawn to the waterline at the point where the
foreside of the stem meets the summer load line.
3. Length between Perpendiculars (LBP): The length between the forward and aft perpendiculars
measured along the summer load line.
4. Amidships: A point midway between the after and forward perpendiculars.
5. Length Overall (LOA): Length of vessel taken over all extremities.
6. Extreme Depth: Depth of vessel at ship’s side from upper deck to lowest point of keel.
7. Freeboard: The vertical distance measured at the ship’s side between the summer load line (or
service draft) and the freeboard deck. The freeboard deck is normally the uppermost complete deck
exposed to weather and sea which has permanent means of closing all openings, and below which
all openings in the ship’s side have watertight closings.
8. Extreme Draft: Taken from the lowest point of keel to the summer load line. Draft marks represent
extreme drafts.
9. Extreme Depth: Depth of vessel at ship’s side from upper deck to lowest point of keel.
10. The summer load line is the primary load line and it is from this mark that all other marks are
derived. The position of the summer load line is calculated from the load line rules and depends on
many factors such as length of ship, type of ship, type and number of superstructures, amount of
sheer, and bow height.
Ship nomenclature is the system of naming the different parts of the ship such as funnel , stern ,
propeller ,bow , deck , anchor etc.

5. Hafez Ahmad Department of Oceanography, University of Chittagong
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Draw ship and label different parts of ship
1) Anchor: An anchor is a heavy metal piece attached to the chain cables and is stored or secured in the
hose pipe during the voyage / ship operation. It can be either permanent or temporary with an additional
sub class of sea anchors. An anchor is made of five major parts; shank, crown, stock, flute and tripping ring.
Function: to secure ships in place against the natural forces such as wind and tide current. They acts as a
holding hand securing them to a definite place.
2) Bow: A bow is the front most part of a ship which cuts the water along its sides as the ship proceeds.
Function: to reduce similar negative forces on ships body; bow are placed on ship assisting easy
propulsion.
3) Bow Thrusters
A bow thruster is a propeller like device fitted on both side of ship’s bow. It is used to increase the
maneuverability of a ship in congested waters under very slow speed like that in canals or near ports.
Function: A ship is maneuvered using propulsion and rudder angle variation.
4 ) Accommodation: It is a place on ship where the crew resides or live. Together with offices, crew cabins,
gym, prayer room ,salon, recreation room, laundry, hospital and galley it is the heart of a ship next to engine
room and bridge.
Function: An accommodation accounts for the living space of the ship. Under maritime labor convention
.it is required by law to provide adequate accommodation facilities to ship’s crew and officers along with
proper recreational facilities.

6. Hafez Ahmad Department of Oceanography, University of Chittagong
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5 ) Deck : A deck is a floor or covering to the ship’s hull structure. A ship can have different decks at
different section or parts of ship; namely upper and lower deck or deck 1, deck 2 and deck 3 in a sequential
downward way.
Function : a deck is the plane that holds the hull structure providing different celling floor to the ship. The
other job it do is to provide space and floor for the equipment and people to stand and work while protecting
them from outside weather.
6 ) Ship’s Hull: A hull is that part of ship that extends below the waterline to cover and protect water from
getting in. Everything that is stored and situated within the main ship structure is covered and protected by
the ship’s hull. It includes the key parts of the ship such as bow, deck, the bottom keel and the both sides
of the ship. They are made up of series of plates jointed together called stakes along with other structural
member such as plating and stiffeners.
Function: role of ship’s hull is to maintain its water tight integrity and reduce water drag. And so hull
plays a major role in determining overall efficiency of a ship.
7 ) Keel: A keel is a part of ship’s hull that is responsible for providing strength to the ships structure;
spreading stress and load equally along its longitudinal sides
Function: it helps stabilize and support ship structure. It also plays an important role increasing the
effective speed of a ship.
8 ) Freeboard: A freeboard stands for the part of ship’s hull located above the waterline. It is the distance
between the upper deck of ship and the point of waterline. The freeboard of a ship is not fixed but rather
depends on the amount of cargo it carries.
Function: The role of freeboard among different parts of ship is to maintain ships stability and avoid it
from sinking.
9 ) Engine Room: An engine room is the power house of the ship located in the lowest most deck on aft
of the ship. It contains important machinery such as main engine, auxiliary engine (Alternator ), shafting,
boiler, fresh water generator, air compressor, calorifier, purifier, incinerator, pumps, heat exchangers,
workshop machineries etc.
Function: The key role of engine room is to hold all the key machinery and auxiliaries required for different
operations on board ship.
10 ) Funnel: A funnel is what from which the exhaust gases are released into atmosphere. We can consider
it as the chimney of the ship. Since the introduction of mechanized ship; it has been an integral part of the
ships structure.
Function: Being one of the parts of ship the function of a funnel is to safely release exhaust gas produced
in engine room to the outside atmosphere.
11 ) Navigation Bridge: If engine room is the heart of the ship; Navigation Bridge is its brain. It is a wide
platform on top of the accommodation from which the ship is controlled.
Function: the function of Navigation Bridge is to provide ample space for officers to look out and
maneuver safely. It also holds necessary equipment’s and controls to change ships speed and its direction
while monitoring outside sea condition and establishing proper means of communication.

7. Hafez Ahmad Department of Oceanography, University of Chittagong
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13 ) Forecastle: A forecastle is the foremost parts of ship. It accounts for the front part of the ships upper
deck and is not more than 7% of total deck
Function: Being one of the key structural parts of ship; a forecastle or the foremost part of the fore deck it
hold all the necessary equipment required for anchoring operation. On navy ships apart from holding
anchoring tools and equipment a forecastle also holds strategic defensive guns position.
14 ) Propeller: It is a fan like mechanical device with blades fitted on the shaft. It rotates with the shaft to
produce much needed thrust to propel a ship. The propeller of a ship produce this thrust by converting the
rotational energy of its blades to pressure energy. This is done by using the difference in pressure generated
on its near and far side of the blade to push the water aside.
Function: the function of propeller in ship is to provide much needed thrust to propel the ship
15 ) Rudder: If propeller is the parts of ship that propels then rudder is the one that makes it steer. Situated
in the aft of propeller; it is a flat hollow structure that moves from port to starboard turning on its axis to
help steer the ship. A rudder is consist of parts such as; rudder trunk, main rudder blade, movable flap,
hinge system, links and rudder carrier bearing. The rudder steers the ship following newton’s third law of
motion similar to that of propeller. It moves to a direction producing resistance to water flow forcing them
to move to the other side. In this very process it produce much needed resultant force for the ship to turn it
to the opposite side of the altered water flow.
Function: A rudder is the parts of ship that make it steer. Based on the newton’s third law of motion it
generates enough resultant force to steer a ship to desired direction. The movement of a rudder is controlled
by steering gear system. A rudder must be capable of moving from 35 degree port to 35 degree starboard;
with the ability of steering gear to move from 35 degree on one side to 30 degree on another in not more
than 28 seconds.
16) Mast: A mast is a vertical ship structure mounted on top of bridge and forward of the forecastle towards
the ship’s bow.
Function: the main job of mast is to hold necessary equipment such as radar receiver, navigation lights,
ships horn, flags and derricks in some cases.
Classify ships according to purposes
By usage By support type
1. Merchant ship
2. Naval and coast guard vessel
3. Recreational vessel
4. Utility tugs
5. Research and environmental ship
6. Ferries
1. Aerostatic support
2. Hydrodynamic support
3. Hydrostatic support
4. Submarine
Transport
1. Cargo ships
2. Passenger ships
3. Container ships
4. Fishing vessel
5. Tug
6. Service craft
7. Supple vessel
8. warships

8. Hafez Ahmad Department of Oceanography, University of Chittagong
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Shipboard fitting
Shipboard fittings mean bollards and bitts, fairleads, stand rollers and chocks used for the normal mooring
of the ship and similar components used for the normal towing of the ship.
What block and tackle , give figure
A block and tackle is a system of two or more pulleys with a rope or cable threaded between them,
usually used to lift heavy loads. The pulleys are assembled together to form blocks and then blocks are
paired so that one is fixed and one moves with the load
Type of shackles with figure
A shackle, also known as a gyve, is a U-shaped piece of metal secured with a clevis pin or bolt across the
opening, or a hinged metal loop secured with a quick-release locking pin mechanism. Shackles are
manufactured in a wide variety of types, styles, sizes, and fabrications.
1.1 Bow shackle
1.2 D-shackle
1.3 Headboard shackle
1.4 Pin shackle
1.5 Snap shackle
1.6 Threaded shackle
1.7 Twist shackle
1.8 Soft shackle
Ship anchoring and mooring, list of common ship anchors
An anchor is a device, normally made of metal, used to connect a vessel to the bed of a body of water to
prevent the craft from drifting due to wind or current. Anchoring is as frequent operation on board as
loading and unloading a cargo.
Ship mooring is the nautical term used to describe the act of securing a vessel to a berth, mooring buoy,
floating platform, or a jetty (dock).
Several other types of anchors are in common use. Lightweight, Danforth, and plow anchors have long.
International Association of Classification Societies (IACS) governs the rules for anchors. IACS enlist
three types of anchors.
1. Normal holding power anchors,:- Union , Byers , Gruson, klipp ,BALDT, SPEK ,HALL
2. high holding power anchors:- AC-14, Pool Tw, Pool N, D’ hone
3. Super high holding power anchors. the Stevin range supplied by Vrijhof Anker
Describe the following commands: hold , check , ease slack double up
Hold : do not let any more line out . To take enough turns on the windlass, capstan or bitts to hold the
mooring line where it is. Do not surge or pay any more line out. If the mooring line begins to take an
excessive strain and is in danger of parting, report this to the bridge immediately.

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Check: hold the mooring line but if it begins to take on an excessive strain, surge or pay out enough line
so that it is in no danger of parting.
Ease : let line out until under less tension but not slacked. To pay out or start to slack the mooring line,
but do not take off all of the tension.
Slack : take all tension off a line . To surge or pay-out and allow the mooring line to form an easy bight.
Double up: means to run additional mooring line or bights or mooring line as needed to make the mooring
secure.
Archimedes' Principle: the upward buoyant force that is exerted on a body immersed on a fluid whether
fully or partially submerged is equal to the weight of the fluid that the body displaces and acts in the
upward direction at the center of the displaced fluid.
B = ρgVdisplaced [V =volume, rho= total submerged in fluid of density, g= acc. Due to gravity]
Buoyancy
Buoyancy (also known as the buoyant force) is the force exerted on an object that is wholly or partly
immersed in a fluid. Buoyancy is caused by differences in pressure acting on opposite sides of an object
immersed in a static fluid.
Discuss tidal behavior of Bangladesh coast
The tides in the coastal and estuarine areas of Bangladesh are semi- diurnal in nature. The coastal zone of
Bangladesh is criss-crossed by large tidal rivers which discharge into the Bay of Bengal. The tides in the
Bay are predominantly semi-diurnal (ie, two high and two low waters every day; the tidal period is 12 hours
25 minutes). The speed of the tidal wave that propagates through the tidal channels depends on the cross-
sectional area of the channel as well as on the water levels of the adjacent rivers. The average tidal range in
the area varies from about 3m on the coast of Hiron Point (Pasur River) to 0.5m 275 km inland. The major
tidal channels of Bangladesh are: Lower Meghna River, Shahbazpur Channel, Hatia Channel, Sandwip
Channel, raymangal, Maloncha, shibsa, Pasur, Baleshwar, karnafuli, sangu, matamuhuri and bakkhali.
Discuss Suitable maritime navigation zones of Bangladesh
Potential conflict of interest between artisanal and industrial fishing regarding fishing area and navigation
many industrial fishers to invade small-scale fishing grounds, thereby reducing their field of action.

10. Hafez Ahmad Department of Oceanography, University of Chittagong
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Problems including diseases encountered by Seafarers/ seamen?
Seafarers are prone to certain serious diseases and health hazards due to the nature of onboard work, change
in climatic conditions, type of cargo carried, working hours, materials being handled, epidemic and endemic
diseases, personal habits etc. The following listed diseases/ illnesses can commonly occur working onboard
merchant marine vessels at sea.
1. Hand Arm Vibration Syndrome (HAVS): Hand transmitted vibration is one of the major hazards
that several seafarers face during their course of work. Operating power tools such as chipping
machine (rust bust), needle guns and hand held grinders is the main reason for such syndrome.
Frequent and prolonged exposure to such power tools results in hand –arm vibration syndrome and
it may lead to permanent disability if not treated in time.
2. Cardio-Vascular Disease (CVD): Cardio- vascular disease is as commonly found in the seafaring
community as in the general population.
3. Musculoskeletal Disorder (MSD): Seafarers were reported to suffer from serious disorders related
to muscular and skeleton structure of their body. The reason was that as offshore operations are
carried out by modern fleets with high end technology and round the clock schedules in all types
of weather conditions, many seafarers work on straight 12 hours shift or 6 on 6 off shifts, which
leaves them with very less time to do any major physical activities
4. Cancer: The most common among them being lungs cancer, renal Cancer, leukemia and
lymphoma. Potential carcinogens such as beryllium, cadmium, lead etc. have been introduced in to
the work place. Officers and crew working on both deck and engine fall prey to this deadly disease
due to continuous exposure to such toxic substances.
5. Sexually Transmitted Disease (STD): Traveling to different countries make seafarers vulnerable
to sexually transmitted diseases such as HIV/ AIDS and venereal diseases like gonorrhea and
syphilis. Seafarers are easily susceptible to unsafe sexual activities and make them a victim of fatal
diseases.
6. Pandemic And Epidemic Diseases: Because of their nature of work, seafarers are bound to visit
many ports in different parts of the world and are thus exposed to various pandemic and epidemic
diseases such as malaria, cholera, yellow fever, tuberculosis etc.
7. Hypertension: Hypertension is mentioned as one of the major occupation hazards onboard
merchant and offshore fleets. Excessive stress, fatigue, loneliness, smoking, consumption of
alcohol, lack of physical activity etc. are the main causes for the same.
Chart and maps
A nautical chart represents hydrographic data, providing very detailed information on water depths,
shoreline, and tide predictions, obstructions to navigation such as rocks and shipwrecks, and navigational
aids. On the other hand, a map is representation, in miniature, on a flat surface, of a portion of the earth’s
surface. It shows physical features; cities, towns, and roads; political boundaries; and other geographic
information. A chart is also a representation of a portion of the earth’s surface, but has been specially
designed for convenient use in navigation. A nautical chart has to do primarily with areas of navigable
water. It features such information as coastlines and harbors, depths of water, channels and obstructions,
and landmarks and aids to navigation.
1. A chart is used by mariners to plot courses through open bodies of water as well as in highly
trafficked areas. Because of its critical importance in promoting safe navigation, the nautical
chart has a certain level of legal standing and authority. A map, on the other hand, is a reference
guide showing predetermined routes like roads and highways.

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2. Nautical charts provide detailed information on hidden dangers to navigation. Maps provide no
information of the condition of a road.
3. Charts are used to represent portions of water or bodies of water with land surrounding them
or land surrounded by them while maps represent the geographical features and relative
positions.
4. Charts give more detailed information about the bodies of water, tidal levels, area underneath
the water’s surface, etc. while maps do not provide information which is not visible by the
naked eye.
5. Charts are used to plot a course. Maps do not help in plotting a course; they show a
predetermined course like a road.
Latitude is an angle which ranges from 0° at the Equator to 90° (North or South) at the poles. Lines of
constant latitude, or parallels, run east–west as circles parallel to the equator.
longitude is the distance on the earth’s surface, east or west of a defined meridian, usually the meridian of
Greenwich, England (0° Longitude), expressed in angular measurements from 180° West (or -180°) to 180°
East.
Passage planning
Passage planning or voyage planning is a procedure to develop a complete description of a vessel's voyage
from start to finish. The plan includes leaving the dock and harbor area, the en route portion of a voyage,
approaching the destination, and finally alongside berth or moored at mooring buoy. This is called 'berth to
berth' passage plan.
There are four distinct stages in the planning and achievement of a safe passage: -
1. Appraisal
This is a process of collecting all the relevant information concerning the intended passage. It may involve
an ocean passage, coupled with an intervening coastal passage consisting of routing systems, and ending
up with a coastal pilotage and berthing schedules. In this stage, the master of the ship discusses with the
chief navigating officer (usually the First Officer), as to how he intends to sail to the destination port.
Taking into consideration master’s guidelines, company’s guidelines, ship’s cargo, marine environment,
and all other factors that may affect the ship, the navigating officer collect , confirm and validate availability
of required up to date navigational publications and charts for intended voyage.
For the ease of planning, this plan is first laid out on a small scale chart, which is later transferred to larger
scale charts, and then minor modifications are made as and when deemed necessary.
2. planning In this stage the intended courses of the ships are actually laid out on the charts of suitable
scale and all additional information is marked. The plan is laid out from pier to pier, including the pilotage
waters. It is a good practice to mark dangerous areas such as nearby wrecks, shallow water, reefs, small
islands, emergency anchorage positions, and any other information that might aid safe navigation. In
addition to the above mentioned things, is it advisable to layout the rate of turn for waypoints and laying
out of PI ranges for suitable objects, if any? Reporting areas should also be clearly marked on the charts.

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3. Execution In this stage, the navigating officers execute the plan that has been prepared. After departure,
the speed is adjusted based on the ETA and the expected weather and oceanographic conditions. The speed
should be adjusted such that the ship is not either too early or late at its port of destination.
4. Monitoring A safe and successful voyage can only be achieved by close and continuous monitoring of
the ship’s progress along the pre-planned tracks. Situations may arise wherein the navigating officer might
feel it prudent to deviate from the plan. In such case he shall inform the master and take any action that he
may deem necessary for the safety of the ship and its crew. This stage is a very important stage wherein all
the deck officers contribute their part to execute the plan. This calls for personal judgment, good seamanship
and experience.
How to write pilotage plan?
Pilotage refers to activities related to the navigation of vessels in which the pilot acts as an advisor to the
master of the vessel and as an expert on the local waters and their navigation. The purpose of pilotage is
to enhance the safety of vessel traffic and prevent environmental damage generated by vessel traffic.
What is LSA?
Life-saving appliances are those appliances that protect human life at sea. Life-saving appliances include:
1. Lifebuoys and life-jackets
2. Immersion suits, anti-exposure suits and thermal protective aids
3. Lifeboats
4. Life-rafts
5. Rescue boats
6. Rocket parachute flares
7. Hand flares
8. Buoyant smoke signals
9. Launching and embarkation appliances
10. Marine evacuation systems
11. Line-throwing appliances
12. General emergency alarm system
13. Public address system
Commonly used onboard lifesaving equipment with respective safety
Safety at sea is a universal responsibility, both of the ship and at a personal level.
1. Lifeboats: There are three types of lifeboats that are generally mandatory on ships, free-fall boats,
partially-covered lifeboats, and totally-covered lifeboats.
2. Rescue boats: As the name suggests, rescue boats are used to rescue people from drowning, near the
shore, or in the deep sea.
3. Davits: Davit systems are used for hoisting, lifting, and storing lifeboats, so that they stay secure at all
times but can be easily removed when necessary.
4. Line-throwing devices: Line-throwing appliances are used to project a from the boat to the person
overboard or from one boat to another and pull the object in distress to safety. It is propelled by an internal
striker mechanism and a rocket and needs to be capable of projecting the line with reasonable accuracy

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5. Ladders: Ladders are a means of getting on or off ships safely, along with the ships’ side. Various types
of ladders can be used to embark on or disembark from a ship, depending on the urgency and the location.
6. Jason’s Cradles: Jason’s cradles are strong nets woven from cloth webbing, used to rescue a man
overboard. They are available in different formats, such as standard units, scramble nets, stretcher units,
etc.
7. Thermal Suits: They are used to conserve body heat in extreme temperatures, up to -30 degrees Celsius
8. Portable fire extinguishers: Portable fire extinguishers are invaluable tools to protect seafarers in case a
fire breaks out on the ocean.
9. Gas detectors and spares: Gas detectors are highly useful in finding the presence of toxic and combustible
gases on ships. These are especially popular in mining, oil and gas, chemical, and industrial sectors, where
there is a high possibility of noxious leaks.
10. Intelligent fire alarm systems: Intelligent systems, such as fire detectors, smoke detectors, etc., are high-
performing devices that allow for fast detection and management of fires. They work using a series of
control and relay modules and probes and are useful in providing advanced warning to protect lives. They
also have the added advantage of low cabling cost.
11. GMDSS equipment: it was a set standard for usage of communication protocol, procedures and safety
equipment to be used at the time of distress situation by the ship. The goal of GMDSS is to virtually
guarantee that complying vessels will be able to communicate with an onshore station at any time, from
any location, in case of distress or to exchange safety-related information.
True north is the direction along Earth's surface
towards the geographic North Pole or True North
Pole. We call the North Pole.
Ship stability
Ship stability is an area of naval architecture and ship design that deals with how a ship behaves at sea,
both in still water and in waves, whether intact or damaged. Stability calculations focus on centers of
gravity, centers of buoyancy, the metacenters of vessels, and on how these interact. There are three types
of equilibrium conditions that can occur, for a floating ship, depending on the relation between the
positions of center of gravity and center of buoyancy.

14. Hafez Ahmad Department of Oceanography, University of Chittagong
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1.Stable equilibrium: when a
vessel is heeled (inclined by an
external force) if she tends to come
back to her original condition, she
is said to be in stable equilibrium.
For vessel to be stable, her GM
(metacentric height) must be
positive.
2.Unstable equilibrium: when a
vessel is heeled, if she tends to
continue heeling further, she is said
to be in unstable equilibrium. An
unstable equilibrium is caused
when the vertical position of G is
higher than the position of
transverse metacenter (M). For a
vessel to be unstable her GM must
be negative i.e. KG must be greater
than KM as shown in the figure.
3. Neutral equilibrium: when a vessel is heeled, if she has no tendency to return to her original
condition or to continue heeling further, she is said to be neutral equilibrium. For a vessel to be in
neutral equilibrium, her GM must be zero i.e. KG equal to KM.
Sextant
Sextant is an essential tool for celestial navigation and is used to measure the angle between the horizon
and a visible object (or two objects at sea.
The sextant is used to measure the following:
1. Vertical Sextant Angle (VSA)
2. Horizontal Sextant Angle (HSA)
3. Altitudes
Principle of the Sextant: When a ray of light suffers two
successive reflections in the same plane by two plane mirrors, the
angle between the incident ray and the reflected ray is twice the
angle between the mirrors
Optical Principles of A Sextant
When a plane surface reflects a light ray, the angle of reflection
equals the angle of incidence. The angle between the first and final
directions of a ray of light that has undergone double reflection in the same plane is twice the angle the two
reflecting surfaces make with each other (Figure 1601).
In Figure, AB is a ray of light from a celestial body.

15. Hafez Ahmad Department of Oceanography, University of Chittagong
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Figure . Optical principle of the marine sextant.
The index mirror of the sextant is at B, the horizon glass at C, and the eye of the observer at D. Construction
lines EF and CF are perpendicular to the index mirror and horizon glass, respectively. Lines BG and CG
are parallel to these mirrors. Therefore, angles BFC and BGC are equal because their sides are mutually
perpendicular.
Angle BGC is the inclination of the two reflecting surfaces. The ray of light AB is reflected at mirror B,
proceeds to mirror C, where it is again reflected, and then continues on to the eye of the observer at D.
Since the angle of reflection is equal to the angle of incidence,
ABE = EBC, and ABC = 2EBC.
BCF = FCD, and BCD = 2BCF.
Since an exterior angle of a triangle equals the sum of the two non adjacent interior angles,
ABC = BDC+BCD, and EBC = BFC+BCF.
Transposing,
BDC = ABC-BCD, and BFC = EBC-BCF. Substituting 2EBC for ABC, and 2BCF for BCD in the first of
these equations,
BDC = 2EBC-2BCF, or BDC=2 (EBC-BCF).
Since BFC=EBC - BCF, and BFC = BGC, therefore
BDC = 2BFC = 2BGC.
That is, BDC, the angle between the first and last directions of the ray of light, is equal to 2BGC, twice the
angle of inclination of the reflecting surfaces. Angle BDC is the altitude of the celestial body. If the two
mirrors are parallel, the incident ray from any observed body must be parallel to the observer’s line of sight
through the horizon glass. In that case, the body’s altitude would be zero. The angle that these two reflecting
surfaces make with each other is one-half the observed angle. The graduations on the arc reflect this half
angle relationship between the angle observed and the mirrors’ angle.

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There are three types of sextants:
1. Nautical Sextant
2. Box Sextant
3. Sounding Sextant
1. Nautical Sextant: Nautical sextant, also called as vernier sextant or marine sextant, is an instrument
mainly used to determine latitude and longitude by measuring angles between two objects. Celestial objects
such as sun, moon, and stars are sighted using a nautical sextant, and angular measurements between them
and the horizon can be determined. Uses of Nautical Sextant
1. It is used for navigational purposes on ships and boats.
2. It is used for astronomical purposes to take angular measurements between celestial bodies.
3. The angles can be measured in any plane i.e. either in the plane of a telescope or in the plane of an
object.
4. Vertical angles measured can be reduced into horizontal angles.
2. Box Sextant: Box sextant is a small pocket instrument which looks like a sextant enclosed in a box and
is 75mm in diameter. Similar to the nautical instrument, it is also used for measuring both the horizontal
and vertical angles. Box sextant is a very small and handy instrument which is easy to carry. It is also used
in ships for celestial navigation, and it also works well even if the ship or boat is moving. Uses of Box
Sextant
1. Box sextant can be used as an optical square by setting vernier to 90o
.
2. Box sextant can be used to measure angles in chain surveying.
3. It is used to check the angles measured by other surveying instruments.
4. Radiation in traversing can be done using box sextant.
3.Sounding Sextant: Sounding sextant is more similar to the nautical instrument and the only difference
is that it has a larger index glass compared to that of the nautical sextant.
Care and maintenance of a sextant
1. Do not put too much stress on the index bar when grasping a sextant
2. Ensure that worm and rack are clean
3. Coat worm and rack with vaseline when not using it for too long
4. Mirrors, lenses and shades should be wiped clean with a soft cloth
5. After each use, gently wipe the index mirror, horizon glass
6. Put it in the box when not using it
7. Do not bump the sextant anywhere
8. Avoid exposure to sunlight
9. Keep sextant stowed away from direct sunlight, dampness, heaters or blowers
The sextant is an expensive, precision instrument which should be handled with utmost care.

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A muster list provides crew members with a plan to manage emergency situations. It gives clear
instructions to be followed in the event of an emergency for every person on board and ensures that all
vital duties are assigned. The muster list also ensures that, on the sounding of the emergency signal,
crewmembers and passengers know where to muster. This allows everyone on board to be readily
accounted for at the outset of an emergency.
Different teams with duties for the individuals of the team for emergencies mentioned in
muster list:
1. Command Team: In-charge master
2. Emergency team 1: In-charge chief officer.
3. Emergency team 2 : In-charge 2nd
engineer (Standby team).
4. Support team : In-charge 2nd
officer includes medical items .
5. Technical team : In-charge chief engineer
Content of muster list:
1. Vessel name / IMO number
2. Emergency duties of all crew and personnel onboard
3. General and emergency alarms
4. person responsible for LSA/FFA maintenance
5. Substitutes for person in-charge ( if incapacitated )
6. Masters signature & Location of Muster station and SOPEP gears
7. Special duties in case of emergency and abandon ship
8. Format to be approved by the flag state
What is fire ? what are the protection measures for fire caution on board ?
A fire needs three elements - heat, oxygen and fuel. Without heat,
oxygen and fuel a fire will not start or spread. A key strategy to
prevent fire is to remove one or more of heat, oxygen or fuel. it is
also important to check/test fire detectors on regular basis. Four
things must be present at the same time in order to produce fire:
 Enough oxygen to sustain combustion,
2. Enough heat to raise the material to its ignition temperature,
3. Some sort of fuel or combustible material, and
4. The chemical, exothermic reaction that is fire.

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Classification of Fuels: four different classifications of fuel.
Class A - Wood, paper, cloth, trash, plastics
Solid combustible materials that are not metals.
Class B - Flammable liquids: gasoline, oil, grease, acetone
Any non-metal in a liquid state, on fire.
Class C - Electrical: energized electrical equipment
As long as it's "plugged in," it would be considered a class C fire.
D Class D - Metals: potassium, sodium, aluminum, magnesium
A fire extinguisher is an active fire protection device used to extinguish or control small fires, often in
emergency situations.
The 4 Classes of Fire Extinguishers: Fire extinguishers aren’t one size fits all; in fact, there are five
different fire extinguisher ratings: A, B, C, and D. Each rating denotes the type of fire the extinguisher
can be effectively used against. Use this guide to determine which class of fire extinguisher you should
purchase to keep your home or workplace safe.
1. Class A fire extinguishers: Class A fire extinguishers are used for ordinary combustibles, such
as paper, wood, cloth, and some types of plastic. These extinguishers typically use water or
certain types of dry chemicals to either absorb heat or coat the fire.
2. Class B fire extinguishers: Fires that originate from flammable liquids and gas can be
extinguished by a class B fire extinguisher. This is the type of extinguisher you’ll want to use on
a fire caused by oil or fuel.
3. Class C fire extinguishers: Class C fire extinguishers are effective against electrical fires from
live wires, panels, and circuit breakers. The extinguisher works by releasing materials that stop
the conduction of electricity.
4. Class D fire extinguishers: Class D fire extinguishers are used on combustible metals. These
include magnesium, sodium, aluminum, and titanium. In order to identify the correct extinguisher
for the risk in your workplace, you need to know what each fire extinguisher type does.
Explanations regarding the different fire extinguisher colors are detailed below:
a. Red – Water: Water extinguishers are safe for use on wood, paper & fabric fires. They are not
safe for use on electrical, flammable liquids or flammable metal fires.
b. Cream – Foam: Foam extinguishers are safe for use on flammable liquid fires; can also be used
for wood, paper, fabric fires. They are not safe for use on electrical or flammable metal fires.
c. Blue – Powder: Powder extinguishers are safe for use on gaseous fires; can also be used for
wood, paper, and fabric, flammable liquid and electrical fires.
d. Black – C02: C02 extinguishers are safe for use on electrical fires; can also be used for flammable
liquid fires. They are not safe for use on wood, paper or fabric fires. They should not be used in a
confined space. And the horn should not be held whilst operating the extinguisher.
Errors of the Sextant
The errors can be classified as
1. Adjustable Errors (adjustable on board), and

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2. Non-adjustable Errors (not adjustable onboard)
Adjustable Errors Of Sextant
 Error of Perpendicularity: This is caused when the index glass is not perpendicular to the plane of
the instrument. To check for this, clamp the index bar about the middle of the arc, and holding the
sextant horizontally, with the arc away from you, look obliquely into the index mirror till the arc of
the sextant and its reflection on the index mirror are seem simultaneous. If in alignment, the error
does not exist. If not, turn the adjustment screw at the back of the index glass, until they are aligned
 Side Error: This is caused by the horizon glass not being perpendicular to the plane of the
instrument. Clamp the index bar at 0 degree 0.0’. Hold the sextant vertically and look at the heavenly
body. Turn the micrometer one way and then the other, while looking at the body. The reflected
image of the body will move above and below the direct image and should pass exactly over it. If
the reflected image passes to the left or right of the direct image, side error exists. This error can be
removed by turning the second adjustment screw (the top screw behind the horizon glass) until the
true and reflected horizons appear in the same line.
 Index Error: This is caused if the index mirror and the horizon glass are not exactly parallel to each
other when the index is set at 0 degree 0.0’. Basically, this is the difference between the optical zero
of the sextant and its graduated zero, termed OFF the arc if the optical zero lies to the right of the
graduated zero and termed ON the arc if the optical zero lies to the left of the graduated zero.
A) By observing the horizon: Clamp the index at 0 deg 0.0’ and, holding the sextant vertical, look
at the horizon. The reflected image and the direct image should appear in a perfect line. If not, turn
the micrometre until they coincide exactly. The reading of the micrometer, ON or OFF the arc gives
the IE
 Error of Collimation: This is due to the axis of the telescope not being parallel to the plane of the
instrument. The telescope is attached to the sextant in such a manner that it cannot tilt. These modern
sextants are therefore not provided with any collimating screws.
Non-Adjustable Errors of Sextant
 Graduation Error: Due to the inaccurate graduation of the main scale on the arc or of the
micrometre/vernier
 Centring Error: Caused if the pivot of the index bar is not situated at the geometric centre of the
arc. This can be caused due to a manufacturing defect or due to careless handling.
 Shade Error: The shades should be so mounted that their glass surfaces are normal to the rays of
light passing through them. If not, the distortion would result. The greater number of shades used,
the greater the chances of distortion.
 Optical Errors: Caused by prismatic errors of the mirrors or aberrations in the telescope lens
 Wear on the rack and worm: This causes a backlash, leading to inconsistent errors. Wearing down
of the worm can be due to lack of lubrication, the presence of dust particles, careless handling

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Pointers on the use of sextant
1. Always check the errors before use
2. Focus the telescope while looking at the horizon and make a mark on the circumference of the stem
3. During use, hold the sextant steady. For this, stand with feet slightly apart for balance with hands
holding the sextant steady
4. While observing the altitude of a celestial body, remember to swing the sextant to the other side, The
body will appear to move along the arc. Measure altitude at the lowest point on this arc
5. Stand as close as far as practicable to the centerline of the ship
Buoys are floating objects heavily anchored to the bottom that are intended to convey information to a
navigator by their shape and color, by the characteristics of a visible or audible signal or a combination of
two or more such features. Buoys are perhaps the largest category of aids of navigation and come in many
shapes and sizes. Lightships fit such a definition but form a separate category by themselves. Buoys
detection at night; these reflect brightly in the beam of a vessel’s searchlight. Many buoys have radar
reflection.
Write down lunching procedure of life buoy , life raft and life boat in case of emergency
1. Release gripes
2. Secure hatches
3. Suitable jackets are to be worn
Launching Raft by Davit:
1. Open the lashing and remove the raft container from HRU by opening the manual slip hook or
bottle screw arrangement.
2. Tie up the one end of the painter of raft into a strong point at deck.
3. Keep the container in the open and attach the davit hook to the given eye in the canister/
container.
Procedure of launching lifeboat:
1. Initial preparation
2. Lower to deck level
3. Secure to embarkation deck
4. Embark personnel
5. Lower to water
6. Letting go
Launching procedure of life boat:
(i) Two persons go inside the Life Boat and passes the end of toggle painter and plugs
the drain.
(ii) Check all lines and falls are clear of Life Boat.
(iii) Make fast the other end of toggle painter on a strong point forward of the ship.
(iv) Remove forward and aft gripes and secure tricing pendant, both person stand by for
passing browsing tackle.
(v) Remove harbor safety pin.

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(vi) Make sure the ship’s side is free of everything, no water or garbage is there.
(vii) Now, one person lift’s the Deadman’s handle slowly which releases the brake.
(viii) The boat along with cradle sides downward till it comes to the embarkation deck. Do
not let the falls over run because tricing pendants are not strong enough to carry the
weight of the boat.
(ix) By pulling bowsing tackle, bring it alongside the embarkation deck.
(x) Crew embark inside the boat.
(xi) Now, tricing pendant is removed and the whole load comes on falls.
(xii) Boat is further lowered with Deadman’s handle.
(xiii) Get the lifeboat away from the ship, rescue any survivor in the water.
How to determine risk of collision: When determining risk of collision a number of factors are involved:
1. Closest distance of approach
2. Type of waterway
3. Vessel size and maneuverability
4. Speed
5. Distance out from closest point of approach
6. Relative bearing
Risk of collision.
(a) Every vessel shall use all available means appropriate to the prevailing circumstances and
conditions to determine if risk of collision exists. If there was any doubt such risk shall be
deemed to exist.
(b) Proper use shall be made of radar equipment if fitted and operational, including long-range
scanning to obtain early warning of risk of collision and radar plotting or equivalent
systematic observations of detected objects.
(c) Assumptions shall not be made on the basis of scanty information, especially scanty radar
information.
(d) In determining if risk of collision exists the following considerations shall be among those
taken into account.
(i) Such risk shall be deemed to exist it the compass bearing of an approaching vessel does
not appreciably change.
(ii) Such risk may sometimes exist even when an appreciable bearing change is evident,
particularly when approaching a very large vessel or a tow or when approaching a
vessel at close range.
Short note:
GPS and DGPS

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The Global Positioning System, is a satellite-based radionavigation system owned by the United States
government and operated by the United States Space Force. At a basic level, GPS enables position
determination through a process of trilateration. This method establishes an unknown location’s position
geometrically by measuring the distances to three known locations. The GPS system has three components:
The space segment, control segment, and user segments. The space component consists of about 31 GPS
satellites.
1. The space component consists of about 31 GPS satellites. The United States Air Force operates
these 31 satellites, plus three to four decommissioned satellites that can be reactivated if needed.
At any given moment, a minimum of 24 satellites is operational in a specially designed orbit. This
orbit ensures that at least four satellites are in view at the same time from almost any point on earth.
2. The control segment is made up of a series of ground stations used to interpret and relay satellite
signals to various receivers. Ground stations include a master control station, an alternate master
control station, 12 ground antennas, and 16 monitoring stations.
3. The user segment of the GPS system involves various receivers from all different types of
industries. National security, agriculture, space, surveying, and mapping are all examples of end-
users in the GPS system. In aviation, the user is typically the pilot, who views GPS data on display
in the cockpit of the aircraft.
How It Works : GPS satellites orbit about 12,000 miles above us and complete one orbit every 12 hours.
They are solar-powered, fly in medium Earth orbit and transmit radio signals to receivers on the ground.
Ground stations use the signals to track and monitor satellites, and these stations provide the master control
station (MCS) with data. The MCS then provides precise position data to the satellites. The receiver in an
aircraft receives time data from the satellites' atomic clocks. It compares the time it takes for the signal to
go from the satellite to the receiver, and calculates distance based on that very accurate and specific time.
GPS receivers use triangulation—date from at three satellites—to determine a precise two-dimensional
location. With at least four satellites in view and operational, three-dimensional location data can be
obtained.
GPS Errors: Ionosphere interference: the signal from the satellites actually slows down as it passes through
the Earth's atmosphere. GPS technology accounts for this error by taking an average time, which means the
error still exists but is limited.
1. Clock error: The clock on the GPS receiver might not be as accurate as the atomic clock on the
GPS satellite, creating a very slight accuracy problem.
2. Orbital error: Orbit calculations can be inaccurate, causing ambiguity in determining the satellite's
exact location.
3. Position error: GPS signals can bounce off of buildings, terrain, and even electrical interference
can occur. GPS signals are only available when the receiver can "see" the satellite, meaning the
data will be missing or inaccurate among tall buildings, dense terrain, and underground.

23. Hafez Ahmad Department of Oceanography, University of Chittagong
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DGPS (Differential GPS) is essentially a system to provide positional corrections to GPS signals. DGPS
uses a fixed, known position to adjust real time GPS signals to eliminate pseudorange errors. An important
point to note is that DGPS corrections improve the accuracy of position data only. The basic difference
between GPS and DGPS lies on their accuracy, DGPS is more accurate than GPS. DGPS was intentionally
designed to reduce the signal degradation. GPS provides the accuracy about 10 meters, but DGPS can
provide accuracy around 1 meter, even beyond that 10 cm.
Basis for comparison GPS DGPS
Number of receivers
used
Only one, i.e., stand-alone GPS receiver Tow, rover and stationary
receivers
Accuracy 15-10m 10cm
Range of the
instruments
global local
cost Affordable as compared to DGPS Expensive
Frequency range 1.1 -1.5 GHz Varies according to agency
Factors affecting
accuracy
Selective availability , satellite timing ,
atmospheric condition
Distance between the transmitter
and rover, ionosphere,
troposphere and multipath
Time coordinate
system
WGS84 Local coordinate system
SONAR (an acronym for Sound Navigation and Ranging) is an acoustic equipment that works with the
principle of underwater sound propagation like echo sounder. SONAR has the four basic components:
1) Transmitter: the transmitter generates pulses of electrical energy and pass on to the
transducer. The pulses of SONAR is meant for long ranges, there are differences in
frequency, power and pulse length. For longer range use lower frequencies are preferred
because they travel further in water. Common sonar frequency range from 20-40KHz. The
power output is increased up to 10 Kw as compared with about 1Kw for an average echo
sounder.
2) Transducer

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3) Receiver and Recorder: signals that are returned from fish shoal or any target to the
transducer are amplified to a sufficient magnitude and then sent to the display unit.
4) Display
Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It
can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and
terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or
microwaves domain, a transmitting antenna, a receiving antenna (often the same antenna is used for
transmitting and receiving) and a receiver and processor to determine properties of the object(s). Radio
waves (pulsed or continuous) from the transmitter reflect off the object and return to the receiver, giving
information about the object's location and speed.
Basically radar works on the same principle as an echo sounder but use radio waves instead of sound
waves. Radar sends radio waves with the help of directional antenna to particular direction. The radio wave
travels with the speed of light that is 3x108
m/s, hit an object if any, on the way of radio wave and bounce
back as echo. Since the waves travel at a constant speed (3x108
m/s), the distance of an object can be
calculated by noting the time interval between transmission of a wave and reception of an echo. If the
travel time of radio wave from antenna to object and back to the antenna as echo is ‘ t’, then the
distance(Range-R) between the antenna fitted vessel and the target object may be determined by the simple
formula:𝑅 =
𝐶𝑇
2
where c = 3 x 108
m/s, the speed of light or radio wave.
The value needs to be taken as 50% because the radio wave pulse travels twice the time of actual required.
Radar signals can be displayed on the Plan Position Indicator (PPI) with rotating vector indicates the
pointing direction of the antenna and hence the bearing of targets.
The advantages of radar are:
1. It is used at night hours and low visibility time.
2. It gives the accurate picture about the objects available around the vessel.
3. It is also useful to trace heavy storms and low pressures areas
4. It is possible to take bearing of any object around a vessel.
5. The distance between the vessel and target can be measured
A compass is an instrument used for navigation and orientation that shows direction relative to the
geographic cardinal directions. The magnetic compass is the most familiar compass type. Magnetic
compasses operate by placing a magnetized needle on a pivot point, which pulls the needle towards the
North and South Poles of the Earth. Compasses revolutionized navigation by including cardinal directions
(North, South, East, and West) combined with the idea of the 360 degree circular plane around the needle.
Gyrocompass is an electro-mechanical device used to find out the direction without adjusting the compass
error such as variation or deviation. The Gyro compass readings are always related to true north.
Gyrocompass will not be influenced by steel structures, electric circuits, etc. this property makes the
gyrocompass a very accurate and reliable than magnetic compass.
Advantages and Limitations
Gyrocompass has the following advantages over the magnetic compass.
1. It seeks the true north instead of the magnetic north.
2. It can be used near the earth’s magnetic poles, where the magnetic compass is useless.

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3. It is not being influenced by surrounding magnetic or electric materials which might influence the
readings of the magnetic compass.
4. Its information can be fed electronically into automatic steering unit or autopilot.
5. It also indicates the ship’s rolling and pitching data needed for instruments used for celestial
navigation.
6. Corrections like variation and deviation need not be applied in the readings of gyrocompass and
the readings are very accurate.
Limitations
1. It requires a constant source of electrical power. In case of any interruption in its operation for any
length of time, nearly four hours may be required for it to settle back into reliable operation.
2. It requires intelligent care, attention and maintenance
3. The accuracy decrease when latitudes above 75o
.
A gyrocompass is a type of non-magnetic compass which is based on a fast-spinning disc and the rotation
of the Earth to find geographical direction automatically. Gyro compasses are pre-eminently used in most
ships in order to detect true north, steer, and find positions and record courses
Working principles of gyro compass
Gyrocompass is working with the high speed gyro rotor (gyroscope) to accurately seek the direction of
true north. It operates by seeking an equilibrium direction under the combined effects of the force of
gravity and the rotation of earth.
Gyrocompass consists of a spinning wheel mounted on
gimbal so that the wheel's axis is free to orient itself in
any way. When it is spun with its axis pointing in some
direction, such a wheel will maintain its axis of rotation.
A gimbal is constructed in such a way that no external
torque acts on the axis of rotation of gyro.
Advantage Disadvantage
1: Seeks geographic (true) north instead of
magnetic.
2: Can be used near the earth’s magnetic poles,
where magnetic compass is useless.
3: unaffected by surrounding metals
1:Gimbal lock occur when two axis align parallel
to each other.
2: Requires a constant source of electrical power
and is sensitive to power fluctuations.
3: requires periodic maintenance by qualified
technicians
Major part of magnetic compass

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The compass consists of a magnetized metal needle that floats on a pivot point. The needle orients to the
magnetic field lines of the earth. The basic orienteering compass is composed of the following parts:
1. Base plate
2. Straight edge and ruler
3. Direction of travel arrow
4. Compass housing with 360 degree markings
5. North label
6. Index line
7. Orienting arrow
8. Magnetic needle
The Principles of the magnetic compass
The Earth itself is a big magnet having north and
south poles, but the poles are not exactly aligned with the rotation axis of the Earth. The magnetic
compass is working with the principle of Earth’s Magnetic Field and shows the magnetic north and south.
The simplest form of compass consists of a magnetized needle free to rotate in a horizontal plane. Such a
needle tends to settle in the magnetic meridian.
A Magnetic compass is a critical piece of marine navigational equipment. Simply put, a magnetised
needle, suspended freely, points North because of the forces caused by the Earth’s magnetic field. Once
North is known, the other directions are easily found.
Advantages of Magnetic compass:
1. No mechanical moving parts.
2. Does not require electrical power.
Limitation of magnetic compass
1. Magnetic compass will not show true north.
2. It will deflected by electric flow.
3. It will deflected by magnetic field.