3 Definitions

3.1 Principal Particulars

3.1.1 L, Rule length

The Rule length L is the distance, in m, measured on the waterline at the scantling draught T_SC from the forward side of the stem to the centre of the rudder stock. L is to be not less than 96% and need not exceed 97% of the extreme length on the waterline at the scantling draught T_SC.

In ships without rudder stock (e.g. ships fitted with azimuth thrusters), the Rule length L is to be taken equal to 97% of the extreme length on the waterline at the scantling draught T_SC.

In ships with unusual stem or stern arrangements, the Rule length is considered on a case-by-case basis.

3.1.2 L_LL, freeboard length

The freeboard length L_LL, in m, is to be taken as 96% of the total length on a waterline at 85% of the least moulded depth measured from the top of the keel, or as the length from the fore side of the stem to the axis of the rudder stock on that waterline, if that be greater.

For ships without a rudder stock, the length L_LL is to be taken as 96% of the waterline at 85% of the least moulded depth.

Where the stem contour is concave above the waterline at 85% of the least moulded depth, both the forward end of the extreme length and the forward side of the stem are to be taken at the vertical projection to that waterline of the aftermost point of the stem contour (above that waterline), see Figure 1.

Figure 1 : Concave stem contour

3.1.3 Moulded breadth

The moulded breadth B is the greatest moulded breadth, in m, measured amidships at the scantling draught, T_SC.

3.1.4 Moulded depth

D, the moulded depth, is the vertical distance, in m, amidships, from the moulded baseline to the moulded deck line of the uppermost continuous deck measured at deck at side. On ships with a rounded gunwale, D is to be measured to the continuation of the moulded deck line.

3.1.5 Draughts

T, the draught in m, is the summer load line draught for the ship in operation, measured from the moulded baseline at midship. Note this may be less than the maximum permissible summer load waterline draught.

T_SC is the scantling draught, in m, at which the strength requirements for the scantlings of the ship are met and represents the full load condition. The scantling draught T_SC is to be not less than that corresponding to the assigned freeboard. The draught of ships to which timber freeboards are assigned corresponds to the loading condition of timber, and the requirements of the Society are to be applied to this draught.

T_BAL is the minimum design normal ballast draught amidships, in m, at which the strength requirements for the scantlings of the ship are met. This normal ballast draught is the minimum draught of ballast conditions including ballast water exchange operation, if any, for any ballast conditions in the loading manual including both departure and arrival conditions.

T_BAL-H is the minimum design heavy ballast draught, in m, at which the strength requirements for the scantlings of the ship are met. This heavy ballast draught is to be considered for ships having heavy ballast condition.

3.1.6 Moulded displacement

Moulded displacement, in t, corresponds to the underwater volume of the ship, at a draught, in seawater with a density of 1.025 t/m³.

3.1.7 Maximum service speed

V, the maximum ahead service speed, in knots, means the greatest speed which the ship is designed to maintain in service at her deepest seagoing draught at the maximum propeller RPM and corresponding engine MCR (Maximum Continuous Rating).

3.1.8 Block coefficient

C_B, the block coefficient at the draught, T_SC is defined in the following equation:

where:

Δ : Moulded displacement of the ship at draught T_SC.

3.1.9 Lightweight

The lightweight is the ship displacement, in t, complete in all respects, but without cargo, consumable, stores, passengers and crew and their effects, and without any liquids on board except that machinery and piping fluids, such as lubricants and hydraulics, are at operating levels.

3.1.10 Deadweight

The deadweight DWT is the difference, in t, between the displacement, at the summer draught in seawater of density ρ = 1.025 t/m³, and the lightweight.

3.1.11 Fore end

The fore end (FE) of the rule length L, see Figure 2, is the perpendicular to the scantling draught waterline at the forward side of the stem.

Figure 2 : Ends and midship

3.1.12 Aft end

The aft end (AE) of the rule length L, see Figure 2, is the perpendicular to the scantling draught waterline at a distance L aft of the fore end.

3.1.13 Midship

The midship is the perpendicular to the scantling draught waterline at a distance 0.5 L aft of the fore end.

3.1.14 Midship part

The midship part of a ship is the part extending 0.4 L amidships, unless otherwise specified.

3.1.15 Forward freeboard perpendicular

The forward freeboard perpendicular, FP_LL, is to be taken at the forward end of the length L_LL and is to coincide with the foreside of the stem on the waterline on which the length L_LL is measured.

3.1.16 After freeboard perpendicular

The after freeboard perpendicular, AP_LL, is to be taken at the aft end of the length L_LL.

3.2 Position 1 and Position 2

3.2.1 Position 1

Position 1 includes:

Exposed freeboard and raised quarter decks.
Exposed superstructure decks situated forward of 0.25 L_LL from FP_LL.

3.2.2 Position 2

Position 2 includes:

Exposed superstructure decks situated aft of 0.25 L_LL from FP_LL and located at least one standard height of superstructure above the freeboard deck.
Exposed superstructure decks situated forward of 0.25 L_LL from FP_LL and located at least two standard heights of superstructure above the freeboard deck.

3.3 Standard height of superstructure

3.3.1 The standard height of superstructure is defined in Table 6.

Table 6 : Standard height of superstructure

*Freeboard length L_LL, in m*	*Standard height h_S, in m*
*Freeboard length L_LL, in m*	Raised quarter deck	All other superstructures
90 < L_LL ≤ 125	0.3 + 0.012 L_LL	1.05 + 0.01 L_LL
L_LL > 125	1.80	2.30

3.3.2 A tier is defined as a measure of the extent of a deckhouse. A deckhouse tier consists of a deck and external bulkheads. In general, the first tier is the tier situated on the freeboard deck.

3.4 Type A and Type B freeboard ships

3.4.1 Type A ship

Type A ship is one which:

Is designed to carry only liquid cargoes in bulk.
Has a high integrity of the exposed deck with only small access openings to cargo compartments, closed by watertight gasketed covers of steel or equivalent material.
Has low permeability of loaded cargo compartments.

Type A ship is to be assigned a freeboard following the requirements specified in the ICLL.

3.4.2 Type B ship

All ships which do not come within the provisions regarding Type A ships stated in [3.4.1] are to be considered as Type B ships.

Type B ship is to be assigned a freeboard following the requirements specified in ICLL.

3.4.3 Type B-60 ship

Type B-60 ship is any Type B ship of over 100 m in length which, according to applicable requirements of ICLL is assigned with a value of tabular freeboard which can be reduced up to 60% of the difference between the ‘B’ and ‘A’ tabular values for the appropriate ship lengths.

3.4.4 Type B-100 ship

Type B-100 ship is any Type B ship of over 100 m in length which, according to applicable requirements of ICLL is assigned with a value of tabular freeboard which can be reduced up to 100% of the difference between the ‘B’ and ‘A’ tabular values for the appropriate ship lengths.

3.5 Operation definition

3.5.1 Multiport

Multiport corresponds to short voyage with loading and unloading in multiple ports.

3.5.2 Sheltered water

Sheltered waters are generally calm stretches of water when the wind force does not exceed 6 Beaufort scale, i.e. harbours, estuaries, roadsteads, bays, lagoons.

3.6 Reference coordinate system

3.6.1 The ship’s geometry, motions, accelerations and loads are defined with respect to the following right-hand coordinate system, see Figure 3:

Origin : At the intersection among the longitudinal plane of symmetry of ship, the aft end of L and the baseline.
X axis : Longitudinal axis, positive forwards.
Y axis : Transverse axis, positive towards portside.
Z axis : Vertical axis, positive upwards.

Figure 3 : Reference coordinate system

3.7 Naming convention

3.7.1 Structural nomenclature

Figure 4 to Figure 8 show the common structural nomenclature used within these Rules.

Figure 4 : Corrugated transverse bulkhead of double hull tanker

Figure 5 : Transverse bulkhead of double hull tanker

Figure 6 : Mid cargo hold transverse section of double hull tanker

Figure 7 : Mid cargo hold transverse section of single side bulk carrier

Figure 8 : Transverse bulkhead of bulk carrier

3.8 Glossary

3.8.1 Definitions of terms

Table 7 : Definition of terms

Terms	Definition
Accommodation deck	A deck used primarily for the accommodation of the crew.
Accommodation ladder	A portable set of steps on a ship’s side for people boarding from small boats or from a pier.
Aft peak	The area aft of the aft peak bulkhead.
Aft peak bulkhead	The first main transverse watertight bulkhead forward of the stern.
Aft peak tank	The compartment in the narrow part of the stern aft of the aft peak bulkhead.
Anchor	A device which is attached to anchor chain at one end and lowered into the sea bed to hold a ship in position; it is designed to grip the bottom when it is dragged by the ship trying to float away under the influence of wind and current, usually made of heavy casting or casting.
Ballast tank	A compartment used for the storage of water ballast.
Bay	The area between adjacent transverse frames or transverse bulkheads.
Bilge hopper tank	The tank used for ballast or for stability when carrying certain cargoes in bulk carriers.
Bilge keel	A piece of plate set perpendicular to a ship’s shell along the bilges to reduce the rolling motion.
Bilge plating	The bilge plating is the curved plating between the bottom shell and side shell. It is to be taken as follows: Within the cylindrical part of the ship: From the start of the curvature at the lower turn of bilge on the bottom to the end of the curvature at the upper turn of the bilge, Outside the cylindrical part of the ship: From the start of the curvature at the lower turn of the bilge on the bottom to the lesser of: A point on the side shell located 0.2D above the baseline/local centreline elevation. The end of the curvature at the upper turn of the bilge.
Bilge strake	The lower strake of bilge plating.
Boss	The boss of the propeller is the central part to which propeller blades are attached and through which the shaft end passes.
Bottom shell	The shell envelope plating forming the predominantly flat bottom portion of the shell envelope including the keel plate.
Bow	The structural arrangement and form of the forward end of the ship.
Bower anchor	An anchor carried at the bow of the ship.
Bracket	An extra structural component used to increase the strength of a joint between two structural members.
Bracket toe	The narrow end of a tapered bracket.
Breakwater	Inclined and stiffened plate structure on a weather deck to break and deflect the flow of water coming over the bow.
Breast hook	A triangular plate bracket joining port and starboard side structural members at the stem.
Bridge	An elevated superstructure having a clear view forward and at each side, and from which a ship is steered.
Buckling panel	Elementary plate panel considered for the buckling analysis.
Builder	The party contracted by the owner to build a ship in compliance with the specifications including Rules.
Bulb profile	A stiffener utilising an increase in steel mass on the outer end of the web instead of a separate flange.
Bulkhead	A structural partition wall sub-dividing the interior of the ship into compartments.
Bulkhead deck	The uppermost continuous deck to which transverse watertight bulkheads and shell are carried.
Bulkhead stool	The lower or upper base of a corrugated bulkhead.
Bulkhead structure	The transverse or longitudinal bulkhead plating with stiffeners and girders.
Bulwark	The vertical plating immediately above the upper edge of the ship’s side surrounding the exposed deck(s).
Bunker	A compartment for the storage of fuel oil used by the ship's machinery.
Cable	A rope or chain attached to the anchor.
Camber	The upward rise of the weather deck from both sides towards the centreline of the ship.
Cargo hold region	See Ch 1, Sec 1, [2.4.3].
Cargo hold	Generic term for spaces intended to carry cargo, liquid or dry bulk.
Cargo tank	Tank carrying cargoes
Cargo tank bulkhead	A boundary bulkhead separating cargo tanks.
Carlings	A stiffening member used to supplement the regular stiffening arrangement.
Casing	The covering or bulkhead around or about any space for protection.
Cellular construction	A structural arrangement where there are two closely spaced boundaries and internal diaphragm plates arranged in such a manner to create small compartments.
Centreline girder	A longitudinal member located on the centreline of the ship.
Chain	Connected metal rings or links used for holding anchor, fastening timber cargoes, etc.
Chain locker	A compartment usually at the forward end of a ship which is used to store the anchor chain.
Chain pipe	A section of pipe through which the anchor chain enters or leaves the chain locker.
Chain stopper	A device for securing the chain cable when riding at anchor as well as securing the anchor in the housed position in the hawse pipe, thereby relieving the strain on the windlass.
Coaming	The vertical boundary structure of a hatch or skylight.
Cofferdams	See Ch 2, Sec 3, [1].
Collar plate	A patch used to, partly or completely, close a hole cut for a longitudinal stiffener passing through a transverse web.
Collision bulkhead	The foremost main transverse watertight bulkhead.
Companionway	A weathertight entrance leading from a ship’s deck to spaces below.
Compartment	An internal space bounded by bulkheads or plating.
Confined space	A space identified by one of the following characteristics: limited openings for entry and exit, unfavourable natural ventilation or not designed for continuous worker occupancy.
Corrugated bulkhead	A bulkhead including corrugations and usually fitted with lower and upper stools.
Corrugation	Plating arranged in a corrugated fashion.
Cross deck	The area between cargo hatches.
Cross ties	Large transverse structural members joining longitudinal bulkheads or joining a longitudinal bulkhead with double side structures and used to support them against hydrostatic and hydrodynamic loads.
Deck	A horizontal structure element that defines the upper or lower boundary of a compartment.
Deckhouse	See Ch 1, Sec 1, [2.4.6].
Deck structure	The deck plating with stiffeners, girders and supporting pillars.
Deck transverse	Transverse PSM at the deck.
Deep tank	Any tank which extends between two decks or the shell/inner bottom and the deck above or higher.
Designer	A party who creates documentation submitted to the Society necessary for approval or for information. The designer can be the builder or a party contracted by the builder or owner to create this documentation.
Discharges	Any piping leading through the ship’s sides for conveying bilge water, circulating water, drains etc.
Docking bracket	A bracket located in the double bottom to locally strengthen the bottom structure for the purposes of docking.
Double bottom structure	The shell plating with stiffeners below the top of the inner bottom and other elements below and including the inner bottom plating.
Doubler	Small piece of plate which is attached to a larger area of plate that requires strengthening in that location. Usually at the attachment point of a stiffener.
Double skin member	Double skin member is defined as a structural member where the idealised beam comprises webs, with top and bottom flanges formed by attached plating.
Duct keel	A keel built of plates in box form. It is used to house ballast and other piping leading forward which otherwise would have to run through the cargo tanks and/or ballast tanks.
Enclosed superstructure	The superstructure with bulkheads forward and/or aft fitted with weather tight doors and closing appliances.
Engine room bulkhead	A transverse bulkhead either directly forward or aft of the engine room.
EPP	Elementary plate panel, the smallest plate element surrounded by structural members, such as stiffeners, PSM, bulkheads, etc.
Face plate	The section of a stiffening member attached to the plate via a web and is usually parallel to the plated surface.
Flange	The section of a stiffening member, typically attached to the web, but is sometimes formed by bending the web over. It is usually parallel to the plated surface.
Flat bar	A stiffener comprised only of a web.
Floor	A bottom transverse member.
Forecastle	A short superstructure situated at the bow.
Fore peak	The area of the ship forward of the collision bulkhead.
Fore peak deck	A short raised deck extending aft from the bow of the ship.
Freeboard deck	Generally the uppermost complete deck exposed to weather and sea, which has permanent means of closing all exposed openings.
Freeing port	An opening in the bulwarks to allow water shipped on deck to run freely overboard.
Gangway	The raised walkway between superstructure, such as between the forecastle and bridge, or between the bridge and poop.
Girder	A collective term for primary supporting structural members.
Gudgeon	A block with a hole in the centre to receive the pintle of a rudder; located on the stern post, it supports and allows the rudder to swing.
Gunwale	The upper edge of the ship’s sides.
Gusset	A plate, usually fitted to distribute forces at a strength connection between two structural members.
Hatch cover	A cover fitted over a hatchway to prevent the ingress of water into the ship’s hold.
Hatchways	Openings, generally rectangular, in a ship’s deck affording access into the compartment below.
Hawse pipe	Steel pipe through which the hawser or cable of anchor passes, located in the ship's bow on either side of the stem, also known as spurling pipe.
Hawser	Large steel wire or fibre rope used for towing or mooring.
Hopper plating	Plating running the length of a compartment sloping between the inner bottom and vertical portion of inner hull longitudinal bulkhead.
HP	Bulb profile in accordance with the Holland profile standard.
IACS	International Association of Classification Societies
ICLL	IMO International Convention on Load Lines, 1966, as amended.
IMO	International Maritime Organisation
Independent tank	A self supporting tank.
Inner hull	The innermost plating forming a second layer to the hull of the ship.
Intercostal	Non-continuous member between stiffeners or PSM.
JIS	Japanese industrial standard.
Keel	The main structural member or backbone of a ship running longitudinally along the centreline of the bottom. Usually a flat plate stiffened by a vertical plate on its centreline inside the shell.
Keel line	Keel line is the line parallel to the slope of the keel intersecting the top of the keel at amidships.
Knuckle	A discontinuity in a structural member.
Lightening hole	A hole cut in a structural member to reduce its weight.
Limber hole	A small drain hole cut in a frame or plate to prevent water or oil from collecting.
Local support members	Local stiffening members which only influence the structural integrity of a single panel, e.g. deck beams.
Longitudinal centreline bulkhead	A longitudinal bulkhead located on the centreline of the ship.
Longitudinal hull girder structural members	Structural members that contribute to the longitudinal strength of the hull girder, including: deck, side, bottom, inner bottom, inner hull longitudinal bulkheads including upper sloped plating where fitted, hopper, bilge plate, longitudinal bulkheads, double bottom girders and horizontal girders in wing ballast tanks.
Longitudinal hull girder shear structural members	Structural members that contribute to strength against hull girder vertical shear loads, including: side, inner hull longitudinal bulkheads, hopper, longitudinal bulkheads and double bottom girders.
Manhole	A round or oval hole cut in decks, tanks, etc, for the purpose of providing access.
Margin plate	The outboard strake of the inner bottom and when turned down at the bilge the margin plate (or girder) forms the outer boundary of the double bottom.
MARPOL	IMO International Convention for the Prevention of Pollution from Ships, 1973 and Protocol of 1978, as amended.
Mid-hold	Middle hold(s) of the three cargo hold length FE model as defined in Pt 1, Ch 7, Sec 2, [1.2.2]
Notch	A discontinuity in a structural member caused by welding.
Oil fuel tank	A tank used for the storage of fuel oil.
Outer shell	Same as shell envelope.
Owner	The party that has assumed all duties and responsibilities for registration and operation of the ship and who on assuming such responsibilities has agreed to take over all the duties and responsibilities on delivery of the ship from the builder with valid certificates prepared for the owner.
Pillar	A vertical support placed between decks where the deck is unsupported by the shell or bulkhead.
Pipe tunnel	The void space running in the midships fore and aft lines between the inner bottom and shell plating forming a protective space for bilge, ballast and other lines extending from the engine room to the tanks.
Plate panel	Unstiffened plate surrounded and supported by structural members, such as stiffeners, PSM, bulkheads, etc. See also EPP.
Plating	Sheet of steel supported by stiffeners, primary supporting members or bulkheads.
Poop	The space below an enclosed superstructure at the extreme aft end of a ship.
Poop deck	The first deck above the shelter deck at the aft end of a ship.
Primary supporting members PSM	Members of the beam, girder or stringer type which provide the overall structural integrity of the hull envelope and tank boundaries, e.g. double bottom floors and girders, transverse side structure, deck transverses, bulkhead stringers and vertical webs on longitudinal bulkheads.
Propeller post	The forward post of stern frame, which is bored for propeller shaft.
Rudder post	After post of stern frame to which the rudder is hung (also called stern post).
Scallop	A hole cut into a stiffening member to allow continuous welding of a plate seam.
Scarfing bracket	A bracket used between two offset structural items.
Scantlings	The physical dimensions of a structural item.
Scupper	Any opening for carrying off water from a deck, either directly or through piping.
Scuttle	A small opening in a deck or elsewhere, usually fitted with a cover or lid or a door for access to a compartment.
Shedder plates	Slanted plates that are fitted to minimise pocketing of residual cargo in way of corrugated bulkheads.
Sheer strake	The top strake of a ship’s side shell plating.
Shelf plate	A horizontal plate located on the top of a bulkhead stool.
Shell envelope plating	The shell plating forming the effective hull girder exclusive of the strength deck plating.
Side frame	A vertical member attached to the side shell in bulk carriers.
Side shell	The shell envelope plating forming the side portion of the shell envelope above the bilge plating.
Single skin member	A structural member where the idealised beam comprises a web, with a top flange formed by attached plating and a bottom flange formed by a face plate.
Skylight	A deck opening fitted with or without a glass port light and serving as a ventilator for engine room, quarters, etc.
Slop tank	A tank in an oil tanker which is used to collect the oil and water mixtures from cargo tanks after tank washing.
SOLAS	IMO International Convention for the Safety of Life at Sea, 1974 as amended.
Spaces	Separate compartments including tanks.
Stay	Bulwark and hatch coaming brackets.
Stem	The piece of bar or plating at which a ship's outside plating terminates at forward end.
Stern	The after end of the vessel.
Stern frame	The heavy strength members attached to the after end of a hull to form the ship’s stern. It includes rudder post, propeller post, and aperture for the propeller.
Stern tube	A tube through which the shaft passes to the propeller; and acts as an after bearing for the shafting. It may be water or oil lubricated.
Stiffener	A collective term for secondary supporting structural members.
Stool	A structure supporting tank bulkheads.
Strake	A course, or row, of shell, deck, bulkhead, or other plating.
Strength deck	The uppermost continuous deck.
Stringer	Horizontal girders linking vertical web frames.
Stringer plate	The outside strake of deck plating.
Superstructure	See Ch 1, Sec 1, [2.4.6].
SWL	Safe working load
Tank	Generic term for spaces intended to carry liquid, such as, seawater, fresh water, oil, liquid cargoes, FO, DO, etc.
Tank top	The horizontal plating forming the bottom of a cargo tank.
Towing pennant	A long rope which is used to effect the tow of a ship.
Topside tank	The tank that normally stretches along the length of the ship’s side and occupies the upper corners of the cargo hold in bulk carriers.
Transom	The structural arrangement and form of the aft end of the ship.
Transverse ring	All transverse material appearing in a cross section of the ship's hull, in way of a double bottom floor, vertical web and deck transverse girder.
Transverse web frame	The primary transverse girders which join the ships longitudinal structure.
Tripping bracket	A bracket used to strengthen a structural member under compression against torsional forces.
Trunk	A decked structure similar to a deckhouse, but not provided with a lower deck.
‘Tween deck	An abbreviation of between decks, placed between the upper deck and the tank top in the cargo tanks.
Ullage	The quantity represented by the unoccupied space in a tank.
Void	An enclosed empty space in a ship.
Wash bulkhead	A perforated or partial bulkhead in a tank.
Watertight	Watertight means capable of preventing the passage of water through the structure under a head of water for which the surrounding structure is designed.
Weather deck	A deck or section of deck exposed to the elements which has means of closing weathertight, all hatches and openings.
Weathertight	Weathertight means that in any sea conditions water will not penetrate into the ship.
Web	The section of a stiffening member attached perpendicular to the plated surface.
Web frame	Transverse PSM including deck transverse.
Wind and water strakes	The strakes of a ship's side shell plating between the ballast and the deepest load waterline.
Windlass	A winch for lifting and lowering the anchor chain.
Wing tank	The space bounded by the inner hull longitudinal bulkhead and side shell.