2. General Ship Knowledge

2.1 Principle dimensions and definitions of ship: Length, Breadth, Depth, LOA, LBP, etc.,

Length Overall (LOA)

The maximum length of the vessel measured from the extreme forward point of the vessel to the extreme after point. It is the maximum length of a vessel's hull measured parallel to the waterline. This length is important while docking the ship.

Length between Perpendiculars (LBP)

The distance between the forward and aft perpendiculars. It is the length of a ship along the summer load line from the forward surface of the stem, or main bow perpendicular member, to the after surface of the sternpost, or main stern perpendicular member. When there is no sternpost, the centerline axis of the rudder stock is used as the aft end of the length between perpendiculars.

Breadth

The maximum beam of the vessel measured from the outside edge of the shell plating on either side of the vessel is the extreme breadth. The beam of the vessel measured amidships, between the inside edge of the shell plating on either side of the vessel, is the moulded breadth.

Ship’s Beam

The widest part of the ship in the transverse athwartships direction.

Depth

The extreme depth of the vessel is measured from the bottom side of the keel to the top of the deck beams, the measurement being taken at the side of the vessel.

The moulded depth is measured from the top side of the keel to the top of the deck beams, at the side of the vessel.

Freeboard

This is the vertical distance, measured at the ship’s side, from the waterline to the top of the freeboard deck edge. The freeboard measurement is taken at the amidships point.

The deck edge is marked by a painted line 25 mm × 300 mm, above the Plimsoll line.

Draft or Draught

This is the vertical distance between the waterline and the bottom of the hull (keel).

Keel

The keel is the bottom-most longitudinal structural element on a vessel.

Tumblehome

The inward curvature of the ship’s side shell plating above the summer load line.

Camber (or round of beam)

The curvature of the deck in the athwartships direction. The measurement is made by comparing the height of the deck at the centre of the vessel to the height of the deck at the side of the vessel.

Sheer

This is the curvature of the deck in the fore and aft direction, measured as the height of the deck at various points above the height of the deck at the amidships point.

Flare

The outward curvature of the shell plating in the foremost part of the vessel, providing more width to the forecastle head and at the same time helping to prevent water coming aboard.

Part of a Ship (Watch Here)

2.2 Ship's Volume & Weight Measurements

2.2.1 Tonnage

All ships constructed on or after 8 July 1982 are measured in accordance with the IMO-International Convention on Tonnage Measurement of Ships 1969. Since 18 July 1994 all ships have needed to comply with the 1969 convention.

"Tonnage" specifically refers to a calculation of the total volume or cargo volume of a ship. Tonnage should not be confused with displacement, which refers to the actual weight of the vessel. Tonnage is commonly used to assess fees on commercial shipping.

Gross tonnage (GT)

It is defined as that measurement of the internal capacity of the ship. Gross tonnage is calculated by measuring a ship's volume (from keel to funnel, to the outside of the hull framing) and applying a mathematical formula.

Net tonnage (NT)

It is that measurement which is intended to indicate the working/earning capacity of the vessel. Port and harbour dues are based on the gross and net tonnage figures. Net tonnage is also calculated by measuring volume of cargo spaces and applying a mathematical formula.

2.2.2 Density & Specific Gravity

Density is defined as 'mass per unit volume'. For example, the mass density of

Fresh Water = 1000 kg per cubic metre or 1.000 tonne/m3

Sea Water = 1025 kg per cubic metre or 1.025 tonne/m3

River/ Dock Water = between 1000 to 1025 kg per cubic metre or 1 to 1.025 tonne/m3

The specific gravity (SG) or relative density of a substance is defined as the ratio of the weight of the substance to the weight of an equal volume of fresh water.

2.2.3 Displacement & Weight

Displacement

The displacement of a vessel is the weight of water it displaces, i.e., the weight of

the vessel and all it contains. It is the immersed volume of the ship in cubic metres × density of the water, expressed in tonnes per cubic metre. It is normal practice to regard the ship’s displacement as being that displacement when at her load draught (load displacement).

Displacement of a vessel can be expressed as an underwater volume, in cubic metres or as a weight determined by the volume x density of the water displaced. In sea water the density constant is taken as 1,025 kg/m3.

Displacement = Lightweight + Deadweight

Lightweight or Light Displacement

This is the weight of the ship when completely empty. It is a mass of a ship with all of its structures including all steels, decks, cargo gears and machineries with boilers topped up to working level. It does not include fuel, lubricating oil, fresh water, water ballast, cargo, stores, crew, passengers and effects.

Deadweight or Deadweight tonnage

It is the displacement at any loaded condition minus the lightship weight. It includes the crew, passengers, cargo, fuel, water, and stores. Like Displacement, it is often expressed in long tons or in metric tons.

Summer Deadweight

Deadweight is defined by the difference in tonnes between the displacement of a ship in water of a specific gravity of 1.025 at the load waterline corresponding to the assigned summer freeboard and the lightweight of the ship. It consists of the total weight of cargo, stores, bunkers, etc., when the vessel is at her summer loadline.

Weight of cargo carriage onboard

Cargo quantity is the deadweight minus non-cargo deductible such as fuel, lubricating oil, fresh water, water ballast, stores, crew, passengers and effects.

2.2.4 Deadweight Scale

A drawing which provides a method for estimating the additional draft or for determining the extra load that could be taken onboard when a vessel is being loaded in water of density less than that of salt water.

This deadweight scale displays columns of scale readings for:

− Freeboard (f).

− Dwt in salt water and in fresh water.

− Draft of ship (mean).

− Displacement in tonnes in salt water and in fresh water.

2.2.5 Load Lines and Zones

Load Line is a special marking positioned amidships that indicates the freeboard of the ship and the legal limit to which a ship may be loaded for specific water types in order to safely maintain buoyancy.

Load Line Marks

shall assign to ships as mandatorily required by International Load Line Convention.
mark in amidships position on both side of the hull.
consist a set of Deck line, Load Line Disc (Plimsoll mark) and Seasonal Load line markings (Load line tree).

There are two types of Load line markings:

Standard (ordinary) Load Line marking –is applicable to all types of vessels.
Timber Load Line Markings – is applicable to vessels carrying timber cargo.

Load Line Zones

The navigable waters of the world are divided into load line zones defined by the International Convention on Load Lines (1966). These geographical areas are described as either

Tropical (T),
Summer (S),
Winter (W) and
Winter North Atlantic

These had been divided into permanent load line zones and seasonal areas. These zones govern the freeboard or draft to which a vessel can be loaded.

Submersion

Except (2) and (3), the appropriate load lines shall not be submerged at any time when the ship puts to sea, during the voyage or on arrival.
In fresh water: the appropriate load line may be submerged by the amount of the FWA. If the density is other than unity, an allowance shall be made for the difference.
When a ship departs from a river or inland waters, deeper loading shall be permitted required for consumption between the point of departure and the sea.

2.3 Parts of The Ship's Structure: Hull, Beams, Frames, Bulkheads, Hatch Covers, Propellers and Rudders, Various Decks, Bilges, Sounding Pipes, Air Pipes, Ventilators

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 is the rear end of the hull. The midships part is the section in the middle of the hull. When one is standing anywhere inside the hull he is facing forward if he faces the stem. When he is facing aft he is facing the stern.

Any line which runs lengthways in a ship is said to run fore and aft and the line joining the stem with the middle of the stern is called the fore-and-aft centre line.

The vertical plane running through the fore-and-aft line divides the ship into two halves. When facing the stem, the starboard side is on your right hand and the port side on your left.

The vertical sides of the hull meet at the bottom of the hull at the keel, which is the backbone or spine of the ship. The curved (vertical) surface at the fore part of the ship is called the bow. The equivalent (sometimes curved) surface at the after part of the ship is called the quarter. The centre part of the ship is referred to as amidships.

Beams

These resist racking, water pressure, longitudinal torsional stresses and local stresses due to weights.

Frames

These resist water pressure, panting, drydocking and racking stresses. May be compared to the ribs of the body, which stiffen the body of the vessel. May be longitudinally or transversely constructed.

Bulkheads

Bulkhead is a vertical partition between compartments. May be in the fore and aft line or athwartships. These resist racking stresses, water pressure, drydocking stresses, heavy weights, hogging and sagging, torsion stresses and shear forces.

Hatch cover

A large steel structure fitted over a hatch opening to prevent the ingress of water into the cargo hold. It may also be the supporting structure for deck cargo. Hatch covers are a moveable structure designed to a weathertight standard. Various designs exist for particular applications.

Types of Hatch Covers

Single-Pull Folding Hatch Cover
Single-Pull Hatch Covers with Long-Chain Drive Operation
Folding hatch covers
Lift-and-roll Piggy-Back covers
Lift-away hatch covers /Pontoon hatch covers
Roll-stowing type hatch cover
Side Rolling hatch covers

Propeller

A ship propeller is a rotating fan-like structure which is used to propel the ship by using the power generated and transmitted by the main engine of the ship.

Types of propellers

Fixed Propeller (Right-handed/Left-handed)
Controllable Pitch Propeller
Twin screw propellers

Rudder

An underwater blade that is positioned at the stern of a boat or ship and controlled by its helm and that when turned causes the vessel's head to turn in the same direction.

Types of rudders

Unbalanced Single Plate Rudder
Semi-Balanced ‘Mariner’-Type Rudder
Balanced Bolt Axle Rudder
Balanced Spade-Type Rudder

Various decks

Deck is the levels or floors of the ship and the main horizontal parts of a ship's structure. There is no one agreed system for naming decks and various name of decks depend on the types of ships and used of purposes.

Forecastle deck: A partial deck above the main deck at the fore part of the ship. It runs from the foremast to the bow.

Main deck: The principal deck of a vessel; the Freeboard Deck is sometimes called Main deck. In some ships, the highest deck of the hull is called Main deck. It can also be the weather deck.

Freeboard deck: The freeboard deck is normally the uppermost complete deck exposed to weather and sea, which has permanent means of closing all openings in the weather part thereof, and below which all openings in the sides of the vessel are fitted with permanent means of watertight closing.

Weather deck: Any deck exposed to the weather, wind and sea condition from outside.

Poop deck: The deck forming the roof of a poop or poop cabin, built on the upper deck and extending from the aft.

Boat deck: The deck area where lifeboats or the ship's gig are stored.

Bridge deck: The deck area including the helm and navigation station, and where the Officer of the Deck/Watch will be found. Uppermost complete deck: The highest deck of the hull, constructed unbroken deck that runs from stem to stern.

Flush deck: Any unbroken deck that runs from stem to stern.

Tween deck: The storage space between the hold and the main deck, often retractable.

Helicopter deck (Heli or Helo deck): Usually located near the stern and always kept clear of obstacles hazardous to a helicopter landing.

Vehicle deck: The decks used to carry vehicles, named in Car carrier and Ro-Ro Ship.

Bilges

the compartment at the bottom of the hull of a ship where water and other drainage collects and must be pumped out of the vessel;
the space between the bottom hull planking and the ceiling of the hold

Normally, there are

Engine room bilges
Cargo hold/Cargo tank bilges
Cargo pump-room bilges
Other spaces (i.e., Forecastle store, Chain locker, voice space) bilges

These bilge compartments are also known as bilge wells, where all the bilge water gets accumulated. The depth and the number of bilge wells depends on the ship’s size, its capacity and the amount of bilge it generates.

Sounding pipes

A pipe which leads down to almost the bottom of a tank to enable the depth of liquid to be measured by a sounding tape. A striking pad must be located on the tank bottom beneath the pipe. Sounding pipes are to end above freeboard deck in easily accessible places and are to be fitted with efficient, permanently attached, metallic closing appliances.

Sounding pipe are fitted and used to measure the level of liquid/water in

Fresh water tanks (FW tank’s sounding pipes are marked and painted with Blue colour)
Ballast Water tanks (BW tank’s sounding pipes are marked and painted with Green colour)
Fuel tanks (Fuel tank’s sounding pipes are marked and painted with Red colour)
Cargo tanks (various as per the colour code system)
Bilges wells (Bilges wells’ sounding pipes are marked and painted with Black colour)
Cofferdams, voice spaces and chain locker, etc. (Gray or Black or other specified)

Sounding pipe are fitted with screw-down caps or cocks and must be kept shut when not in use, to prevent potential flooding.

Air pipes and ventilators

Air pipe – A pipe provided to equalize the tank pressure with the atmospheric one while the tank is being emptied or filled. Air pipes terminating on the open deck shall be fitted with approved air pipe heads. However, air pipes from the fuel oil settling and service tanks should be led to the funnel in order to eliminate the risk of water ingress due to a broken pipe or head.

Ventilator – Any grid, vent pipe or opening through which air can enter or leave a space. Vent pipes on the weather deck can be a source of water ingress to lower deck areas. Strong built-in vent trunks are safer solutions.

2.4 Ship's Tanks such as Peak Tanks, Double Bottom Tanks, Side Tanks, Wing Tanks

Tank

An enclosed space formed by the permanent structure of a ship and which is designed for the carriage of liquid in bulk.

If use to storage the fuel oil/diesel oil, name as Fuel Oil Tank/Diesel Oil Tank.

(FOT/DOT)

If use to storage the fresh water/ballast water, name as Fresh Water Tank/Ballast Water Tank. (FWT/BWT).

If use to storage the dirty water, name as Gray (Grey) water Tank.

If use to storage the oily water mixture (sludge from Engine room), name as Sludge Tank. If use to storage the oily water mixture (residues from Cargo spaces), name as Slop Tank.

If designate to carry the cargo oil/liquid chemical, name as Cargo Tank. If designate to store the sewage, name as sewage Tank.

Base on purposes, other names of tanks on ship are Settling tanks, Service tanks,

Over flow tank, Lubricating oil tanks, Main Engine Crank Case (M.E.C.C) Oil Tank, etc.…

Depend on the construction and location of the tanks, types of tanks are known as follows;

Forepeak tank (FPT)
Afterpeak tant/Aft peak tank (APT)
Deep Tank (Deep TK)
Double Bottom tank (DBT)
Top side tank (TST)
Side tank/ Wings tank
Heeling tank

Forepeak tank (FPT): The watertight compartment situated forward of the collision bulkhead.

Aft peak tank (APT): A compartment located aft of the aftermost watertight bulkhead. Fore peak and aft peak tank is generally used as Ballast water tank and fresh water tank respectively.

Double bottom tank: A tank constructed at the bottom of a ship between the inner bottom and the shell plating. Generally, it is to be fitted from the collision bulkhead to the afterpeak bulkhead and shall be continued out to the ship’s sides.

Top Side Tank: It is tank of triangular configuration fitted at both shoulders/wings of the cargo holds. Mostly constructed on bulk carrier. Their purpose is to carry ballast water, but topside tanks of some bulk carrier are also designed to carry grain cargo.

Side tank/ Wing tank (Lower Hopper Tanks): These tanks are on the sides of the vessel within the bottom wing of each cargo hold and are the continuation of the DB tanks. They provide additional space for ballast and the sloping margins of the tank top to collect the cargo in the central part of the hold.

Heeling tanks: These are a kind of side/wing tanks which correct the heel of ship, especially during cargo operation.

2.5 Void Space, Longitudinal and Transverse Cofferdam

Void space

Void space is an enclosed space in the cargo area external to a cargo containment system, other than a hold space, ballast space, fuel oil tank, cargo pump or compressor room, or any space in normal use by personnel. Void space will not be used in most case. Openings to void spaces adjacent to cargo tanks should be so designed and fitted as to prevent the entry of water, sulfur or cargo vapor.

Cofferdam (Coffer + Dam)

Coffer is a chest or a box for storing items or a hull of monuments.

Cofferdam is an isolating space arranged so that compartments on each side have

no common boundary; a cofferdam may be located vertically or horizontally.

A cofferdam on tankers may be a void space or a ballast space.

Cofferdam avoids intermixing of two different liquid when there is a leak from the

boundary separating the two liquids.

The cofferdam is provided with manholes for entry and inspection. It is also provided with sounding pipe. It is always maintained dry to detect an early leak.

2.6 Ship Structural Arrangement

2.6.1 Different elements in ship construction

Keel

A centerline plate passing from the stem to the stern frame; referred to as a flat plate keel; generally, of increased scantlings. Though it can also be in the form of steel bar but it is very rare these days.

Nowadays, keel of the ship is the bottom most plate of the ship laid along the entire length of the ship. Floors or bottom transverses are attached to the keel.

Duct keel: A hollow passage within the double bottom along the centerline of the vessel used for piping.

Shell plating: Shell plating is the steel plate used on the shell of the ship and the plates forming the outer side and bottom skin of the hull.

Steel plates of various size, which, when joined together, form the sides of the ship’s hull. The plates forming the outer side and bottom skin of the hull. The shell plating is of crucial importance to the longitudinal strength of the ship structure.

One of the main purposes of shell plating is to provide watertight skin of the ship. Shell plating is divided into two parts;

Bottom shell plating
Side shell plating

Strake: A strip of plating used in the outer hull structure, decks or bulkheads; for example

Bilge strake, Keel strake, Sheer strake, Garboard strake etc.

Girder: A collective term for primary supporting structural members.

Girders are also named according to its location and types of girders are as follows;

Center girder
Web girder
Deck girder
Double bottom girder
Hull girder
Intercostal girder
Longitudinal girder

Stiffners: A secondary supporting structural member: an angle, T-bar, channel, built-up section, etc.

Purpose of stiffeners

To prevent the planes (plate fields i.e., the shell, decks, bulkheads and tank top) of a ship from distorting under influence of the shearing loads, bending moments and local loads, they have to be stiffened.

Stringers: A term applied to a fore-and-aft girder running along the side of a ship at the shell and also, to the outboard strake of plating on any deck. If same stiffener is required to be welded in horizontal direction, it will be called stringer.

Deck plating: The plating forming the covering of a deck, considered collectively. It is steel plate that forms the various deck of the ship. As per the location, these can be given a more specific name to the deck plating, i.e., accommodation deck plating or main deck plating.

2.6.2 Bow part (Force end structure)

The foreship is the part of the ship between the stem and the collision or forepeak bulkhead, and the adjacent section.

The space in front of the collision bulkhead is the forepeak. The forepeak tank is the lowest space in the forepeak and can be divided into a lower and an upper forepeak tank. The forepeak tank is usually used as a ballast tank.

2.6.3 Bulbous Bow

Bulbous Bow

A bulbous bow is a protruding bulb at the bow (or front) of a ship just below the waterline. The bulb modifies the way the water flows around the hull, reducing drag and thus increasing speed, range, fuel efficiency, and stability.

2.6.4 Fore part (Cargo hole structure)

2.6.5 Midship Part

2.6.6 Aft Part (Engine Room)

2.6.7 Stern Part

2.6.8 Stern Frame

2.6.9 Stern Tube

A stern tube is a hollow tube that runs through the bottom of the ship from the main engine to the propeller. The ship's tail shaft (or propeller shaft), which transfers power from the main engine, runs inside the stern tube and connects to the propeller.

2.6.10 Outfitting on Deck

Outfitting related to Mooring & Anchoring arrangements

Bitts: Vertical tubular steel posts; two of them are fastened to the rectangular base of a bollard.

Bollard: A rectangular base welded to the deck of the ship, upon which two vertical bitts are welded. Bollards are used to secure the mooring lines.

A single bitt on ships may also be referred to as a bollard around which the eye of the rope is attached. The term ‘bollard’ is usually applied to a mooring post found on the quayside and ‘bitts’ to the twin posts found on ships.

Chock: A guide for a mooring line, or steel towing wire which enables the line to pass through a ship bulwark or other barrier.

Panama-type fairlead, Panama chock: A non-roller type fairlead mounted at the ship side and enclosed so that mooring lines may be led to shore with equal facility either above or below the horizontal. Strictly refers to fairleads complying with Panama Canal Regulations, but often applied to any closed fairlead or chock.

Fairlead: A guide for a mooring line which enables the line to be passed through a ship bulwark or other barrier, or to change direction through a congested area without snagging or fouling.

Pedestal roller fairlead, pedestal roller guide: Part of mooring equipment used to change the direction of a rope or wire in order to provide a straight lead to a winch drum.

It is generally referred to as an ‘Old man’ or a ‘Deadman’.

Cable compressor: It is separated fitting of chain holder which is intended for emergency towing arrangement. Mostly fitted on tanker vessels.

Other outfitting on deck are;

Outfitting related to Lifting gear arrangements
Outfitting related to cargo access, closing/opening arrangements
Outfitting related to cargo operation/lashing arrangements
Outfitting related to piping arrangements
Outfitting related to deck machinery arrangements
Outfitting related to boarding arrangements and etc.

Typical layout of a general cargo vessel (Admiralty manual of seamanship).

A merchant ship has holds where they store cargo. They are below the upper deck and are numbered consecutively from forward to aft. The decks below the upper deck are referred to as ‘tween decks’. The lowest part of the hold is referred to as the lower hold. A flat is a platform which does not run the length or breadth of the ship, ie the tiller flat (the compartment situated right aft where the steering motors are mounted).

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