Shipboard Plate and Construction Terms

‘A’ Frame – A support structure to provide rigidity to the shaft of a twin-propeller construction. It is shaped like a turned-over ‘A’, hence its name, where the propeller shaft is supported at the apex of the structure.

Aft Peak Tank – A water tank set right aft of the vessel. It will either be a designated freshwater tank or a ballast water tank used for adjusting the ship’s trim.

Beam Knees – Triangular steel plates secured between beams or half-beams and the side frames. They tend to compensate for racking stresses and localised stresses from heavyweights.

Beams – These are usually in the form of ‘T’ bulb bars, ‘H’ girders or channel bars, which are designed to stiffen and support throughout the vessel’s length. They compensate for water pressure, panting, dry docking and racking stresses.

Bearing Pintle – Described by being the lowest bearing point of the ship’s rudder, when the rudder is of a type which is supported within the structure of a stern frame arrangement.

Bitter End – The term given to the end of the ship’s anchor cable. It is often slipped in drydock for the purpose of ranging cables on the floor of the dock for inspection.

Boss Plate – The shell plate in a position either side of the propeller boss.

Bulkhead Deck – Defined as the deck up to which all the main watertight transverse bulkheads extend.

Bulkheads – The steel vertical partitions found between compartments. They compensate for racking, water pressure, dry docking and heavyweight stresses. They also combat hogging, sagging and shear forces.

Ceiling – A protective cover, usually of wood, which is set over the tank tops in way of the hatchway of a cargo hold aboard a general cargo vessel.

Chain Locker – A compartment usually positioned forward of the collision bulkhead which is used to accommodate the volume of chain cable attached to each of the ship’s anchors. Locker maintenance is usually carried out when the vessel is drydocked because the cables are normally ranged on the dock flor, freeing up the space to allow inspection, cleaning and painting to take place.

Coff Plate – A ‘U’-shaped plate found between the end of the keel and the bottom of the stern frame.

Collision Bulkhead – An athwartships bulkhead positioned at the forepart of the vessel. As the name suggests, it is meant to sustain the rest of the ship’s length following an impact such as when in a collision. The bulkhead is stiffened and considered watertight, although it is pierced by a single pipe usually to accommodate the fore peak pumping arrangement. It would be one of the structural members that would be visually sighted when carrying out a damage assessment following a collision, to detect cracks or similar damage which might lead to consecutive flooding of the vessel.

Decks – Horizontal steel plates providing deck flooring throughout the ship’s length. Decks compensate for all longitudinal and athwartships stresses and reduce the hogging, sagging, shearing and bending forces affecting the vessel.

Deep Tank – A steel tank arrangement generally used for the carriage of liquid/bulk cargoes or ballast water. They are often found beneath a lower tween deck of a general cargo vessel or set either side of a shaft tunnel.

Double Bottom Tanks – The internal tanking system found at the bottom of a ship, positioned either side of the keel. Usually employed for the carriage of fuel oil, ballast water or diesel oil.

Duct Keel – The name given to a tunnel structure which tends to run from the fore end of the engine room to the collision bulkhead. It is usually large enough to accommodate an upright walking man. Access is normally gained through a manhole cover situated at the bottom of the engine room near the fore and aft line and close to the forward engine room bulkhead. Its function is to carry pipelines through the forward length of the vessel. There is no need for an aft ‘duct keel’ because the same function is available with the shaft tunnel arrangement.

Floor – An athwartships steel member which can be either a ‘watertight floor’, ‘solid floor’, or a ‘bracket floor’. They act in way of the ship’s frames in the double bottom structure of the vessel and interconnect the ‘intercostal’ and ‘longitudinal’ members. Solid plate floors have lightening holes cut in and these serve to reduce the overall weight of the ship (and subsequent tonnage dues) as well as providing access for tank inspection personnel.

Fore Foot – The area of the shell plating where the stem of a ship is joined to the keel.

Fore Peak Tank – A water tank set under the fo’c’sle head. It is usually a designated Water Ballast Tank, used for trimming the vessel.

Frames – Probably best described as the steel ribs of the ship. They act to stiffen the shell plating of the ship’s hull and resist the stresses caused by water pressure when the vessel is at sea. They also resist dry docking stresses and racking stresses. Ships are built either transversely or longitudinally framed.

Ganger Length – A short length of the ship’s anchor cable which is found between the ‘Anchor Crown ‘D’ Shackle’ and the first joining shackle of the cable. It may contain a swivel and usually is made up of only a few links.

Garboard Strake – The first strake of the shell plate, either side and next to the keel plate.

Gusset Plates – Triangular plates often used for joining angle bar to plate steel.

Hat Box – A term given to a suction or filing well found in deep tank construction. It can operate as a bilge suction or allow filing operations for water ballast. The line can also be blanked off

Hawse Pipes – The usual position for the stowage of the ship’s anchors. The hawse pipes facilitate the run of chain cable when letting go the anchor.

Hopper Tanks – Side wing tanks found in the region of the lower cargo hold of a Bulk Carrier vessel.

Intercostals – A longitudinal strength member of the ship’s bottom structure. They tend to tie together the athwartships floors. It is fist and foremost a steel girder used in way of the
plate keel as a centre line intercostal, running from forward to aft.
Side intercostals positioned either side of the centre line are aligned at a suitable distance apart to afford continuity of strength. Centre line and side intercostals are generally inter spersed with secondary longitudinals but of a smaller depth size and are considered to be a lesser strength member.

Keel Rake – The inclination of the line of the keel to the horizontal.

Keel (Plate) – The centre line plate at the bottom of the ship. Not all keels are plate keels.

Lightening Holes – These are round or oval holes punched into floors and intercostals to lighten the structure and allow access into tank areas.

Limbers – Coverings over the bilge bays at the bottom of the cargo compartments. Old tonnage usually had portable ‘limber boards’ manufactured in timber. More modern tonnage usually has hinged steel plates which can be lifted to permit inspection of bilge areas.

Longitudinals – see Intercostals.

Margin Line (Margin of Safety Line) – Established by the Bulkheads Committee of 1914, which recommended a 3-inch line of safety below the top of the ‘bulkhead deck’, measured at the ship’s side. As agreed by the SOLAS convention 1929.

Margin Plate – A longitudinal plate which passes alongside the extreme ends of the floors in way of the ‘turn of the bilge’. The construction provides an end plate, situated either side of the vessel, to the ‘Double Bottom’ tank system.

Mud Box – The space contained at the bottom of the anchor chain locker. It is usually covered by wooden gratings and accommodates mud and waste residues from the anchor cable following the anchor being heaved in. The mud box is rarely accessible except in a dry dock situation when cables have been ranged on the flor of the dock and this presents an
ideal opportunity to clean and paint the space.

Oxter Plate – An ‘S’-shaped shell plate, found around the stern quarters of the vessel at the point where the body of the ship falls away towards the boss plate.

Panting Beams – Athwartships steel members found in the forepart of the vessel, abaft the stem, and forward of the collision bulkhead. They are intended to brace the ship’s side plating in the area of the bow to reduce the in/out movement of the plates as increased pressure is brought to bear, by the depth of sea water affecting the hull, when the ship is
pitching.

Panting Stringers – Horizontal steel plates which interconnect the panting beams found at the ship’s sides, in the fore part of the vessel.

Pillars – Found extensively in general cargo vessels for upper and intermediate deck support. They compensate for stresses caused by heavy weights, racking, dry docking and water pressure stresses.

Propeller Hub – A central covering that is found in the middle of the propeller designed to cover the locking propeller nut securing.

Propeller Shaft – A rotational shaft, driven from a main engine source, which generates propeller movement. Multiple screw vessels will have a multiple propeller shaft arrangement. With the advent of ‘pod propulsion units’ many ships have been able to dispense with propeller shafts.

Reaction Fins – Steel plates set in ‘ducting’ in a position forward of the propeller in order to deflect water flow more favourably to the propeller blades.

Rise of Floor – An angular measurement taken next to the keel which indicates the angle between the base line of the top edge of the keel and the bottom shell plating.

Rudder Carrier – Internal support set about the rudder post for accommodating the weight
of the rudder construction. Often incorporates a stuffing box arrangement with a rudder
post guide to prevent water ingress as the post passes through the hull.
Rudder Post – The member that supports the position and weight of the rudder. The post passes through the hull via a watertight gland arrangement and is allowed to rotate in order to angle the rudder.

Rudder Trunk – The compartment that the rudder post passes through the ship’s hull, from the steering arrangement to the rudder itself.

Sacrificial Anodes – A method of corrosion reduction employed for many years on steel hulled vessels where dissimilar metals or different grades of steel are employed, e.g. around the stern plates and the propeller. The use of sacrificial anodes served to reduce corrosive activity on the hull, impressing a current flow to cause direct corrosion towards resistant
anodes. They were usually made of zinc or other similar metal.

Scantlings – A term used to describe the measurements of steel sections used in ship construction.  This term was originally applied to the size of lintels in wood-built ships.

Shaft Tunnel – The space which lies in the fore and aft line which accommodates the propeller shaft. This space is usually fitted with a side walkway to allow inspection of the propeller shaft, bearings, and any stuffing box or watertight glands where the shaft passes through the hull.

Sheer Strake – This is the uppermost strake of ship’s plate beneath the ship’s gunwale and in a position which is usually adjacent to the uppermost continuous deck.

Shell Plating – The steel sides of the vessel are constructed from a series of steel plates referred to as the ‘shell plating’. The shell plates compensate for all stresses incurred by the vessel, including localised stresses, e.g. shell doors.

Sole Piece – The name given to the lowest part of the stern frame which extends from right aft to the keel plate. When a vessel grounds, because more often than not the vessel is trimmed by the stern, the sole piece is most likely to make fist contact with the ground, resulting in a broken sole piece. When the vessel dry docks, it is one of the rare occasions that the vessel might be docked stern fist as opposed to bow fist, which is the norm.

Spar Ceiling – Wooden cargo battens which cover the steel frames of a general cargo vessel to prevent cargo coming into contact with the steelwork and so preventing cargo sweat.

Spectacle Frame – A special support frame set in way of the twin propeller shafts of a twin-screw vessel. The frame is found at the after part of the vessel in way of the fie lines of the ship.

Spurling Pipes – Vertical tubes designed to carry the anchor cable from the upper deck down to the lower chain locker. (Warships: Navel Pipes.)

Stealer Plate – An ‘L’-shaped plate found generally at the extremities of the vessel where deck stringers or hull plates are reduced from a triple width to a double width.

Stem Rake – The inclination of the stem line to the vertical.

Stern Frame – A supporting structure at the after end of the ship, which provides rigidity and strength to the rotating propeller and the rudder stock.

Strake – A term which describes a continuous row of steel plate, e.g. Garboard Strake.

Struts – Supporting steel work positioned to provide securing between the propeller shafts and the stern quarters of the outer hull.

Stuffing Box – The term is given to a gland connection where the tail shaft or rudder post pass through the hull. The packing inside the gland can be compressed tight, to ensure a watertight seal. It is a common task when in dry dock for the packing to be renewed.

Tail End Shaft – The part of the propeller shaft which is positioned most aft and accommodates the ship’s propeller. It is usually tapered and the propeller is ‘keyed’ into position. The propeller hub would be turned onto the shaft end. This is an important inspection area when in dry dock because it is piercing the watertight integrity of the hull. As such, it is often fitted with a stuffing box or an alternative watertight lining system to reduce the possibility of water ingress. It would be usual practice to renew packing or lining of the arrangement once the shaft has been removed in dock.

Tank Side Bracket – An interconnecting plate found between the margin plate and the frames. Its function is to strengthen the connection at the turn of the bilge in way of the double bottom construction.

Tank Tops – Tank tops are the covering deck plates over the double bottom structure and are found at the bottom of the ship’s holds. They are often covered by a protective wood shield known as the ‘ceiling’ which has a tendency to protect the plates from heavy duty cargoes being landed either intentionally or accidentally.
Windlass – A mooring winch used extensively for heaving in and lowering the ship’s anchor cable. It may be centre line fitted or operated as a split windlass to accommodate port and starboard anchors.

Windlass Bed – Steel bed plate secured to the fore mooring deck of a vessel to accommodate the windlass.

Windlass Brakes – Band or disc brakes designed to control the movement of the anchor chain cable. These would normally be thoroughly inspected during the period of dry docking and brake linings would be renewed if required.