TERMS OF HULL STRUCTURE

Hull Terms & Hull Survey

Hull Terms

2.1 General

Accommodation Ladder

is a portable set of steps on a ship’s side for people

boarding from small boats or from a pier.

Aft Peak Bulkhead

is a term applied to the first main transverse watertight

bulkhead forward of the stern. The aft peak tank is the compartment in the

narrow part of the stern aft of this last watertight bulkhead.

Bay

is the area between adjacent transverse frames or transverse bulkheads.

Bilge Keel

is a piece of plate set perpendicular to a ship’s shell along her bilges

for about one third her length to reduce rolling.

Bilge Strake

is the strake at the turn of bilge extending outward to a point where

the side rises vertically.

Breast Hook

is a triangular plate bracket joining port and starboard side

structural members at the stem.

Bulkhead Deck

is the uppermost continuous deck to which transverse watertight

bulkheads and shell are carried.

Bulkhead Structure

is the transverse or longitudinal bulkhead plating with

stiffeners and girders.

Bulwark

is the vertical plating immediately above the upper edge of the ship’s

side surrounding the exposed deck(s).

Cargo Area

or

Cargo Length Area

is that part of the ship that contains cargo

holds and cargo / slop tanks and adjacent areas including ballast tanks, fuel

tanks, cofferdams, void spaces and also including deck areas throughout the

entire length and breadth of the part of the ship over the mentioned spaces.

Cargo Hold Bulkhead

is a boundary bulkhead separating cargo holds.

Cargo Port

is a door or port in a ship’s side for the loading or discharge of cargo

or stores.  Also called side port.

Carlings

are supports usually of flat plate, welded in a fore and aft direction

between transverse deck beams to prevent distortion of the plating.

Casing

is the covering or bulkhead around or about any space for protection.

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Ceilings

is wood sheathing or planking fitted on various parts of the ship such as

tank tops, ship’s sides and bulkheads to protect the ship’s structure from

damage and also used to protect the cargo from damage.

Coaming

is the vertical boundary structure of a hatch or skylight.

Cofferdams

are

spaces between two bulkheads or decks primarily designed as

a safeguard against leakage of oil from one compartment to another.

Collision Bulkhead

is the foremost main transverse watertight bulkhead.

Companion Way

is a weathertight entrance leading from a ship's deck to spaces

below.

Confined Space

is a space identified by one of the following characteristics:

limited openings for entry and exit, unfavorable natural ventilation or not

designed for continuous worker occupancy.

Cross Deck

is the area between cargo hatches.

Cross Ties

are used to support the longitudinal bulkheads of oil tankers against

hydrostatic and hydrodynamic loads.

Dead Covers

are

plates of bronze or steel working on a hinge serving to protect

the glass port light in heavy weather.  Also called dead light.

Deck House

is a structure on the freeboard or superstructure deck not extending

from side to side of the ship.

Deck Structure

is the deck plating with stiffeners, girders and supporting pillars.

Deep Tank

is a tank extending from the bottom or inner bottom up to or higher

than the lowest deck.

Discharges

are any piping leading through the ship's sides for conveying bilge

water, circulating water, drains etc. Also called Overboard Discharge.

Double Bottom Structure

is the shell plating with stiffeners below the top of the

inner bottom and other elements below and including the inner bottom plating.

Duct Keel

is a keel built of plates in box form extending the length of the cargo

hold.  It is used to house ballast and other piping leading forward which otherwise

would have to run through the cargo holds.

Enclosed Superstructure

is the

superstructure with bulkheads forward and/or

aft fitted with weather-tight doors and closing appliances.

Equipment Number

is used by classification societies mainly to determine the

size and number of anchors and chain cables for a new ship.

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Floor

is a bottom transverse member.

Flush Deck Ship

is a ship that has no superstructure on the freeboard deck.

Forecastle

is a short superstructure situated at the bow.

Forepeak

is

the area of the ship forward of the collision bulkhead.

Freeboard Deck

is normally the uppermost complete deck exposed to weather

and sea, which has permanent means of closing all exposed openings.

Freeing Port

is an opening in the bulwarks to allow water shipped on deck to run

freely overboard.

Gangway

is the raised walkway between superstructure such as between

forecastle and bridge or between bridge and poop.

Girder

is a collective term for primary supporting structural members.

Gunwale

is the upper edge of the ship's sides.

Gusset

is a triangular plate, usually fitted to distribute forces at a strength

connection between two structural members.

Hatch Coaming

is the vertical plating built around the hatchways to prevent

water from entering the hold; and to serve as a framework for the hatch covers.

Hatch Covers

are wooden or steel covers fitted over a hatchway to prevent the

ingress of water into the ship s hold and may also be the supporting structure for

deck cargo.

Hatch Ways

are openings, generally rectangular, in a ship’s deck affording

access into the compartment below.  Also called hatches.

Hopper Side Tanks

are tanks used for ballast or for stability when carrying

certain cargoes in bulk carriers.  Also referred to as topside wing ballast tanks

and bottom hopper tanks.

Independent Tank

is a self-supporting tank.

Keel

is the main structural member or backbone of a ship running longitudinal

along centerline of bottom.  Usually a flat plate stiffened by a vertical plate on its

centerline inside the shell.

Margin Plate

is 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.

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Midship Section

is the cross section through the ship, midway between the

forward and after perpendiculars.

Pipe Tunnel

is 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 holds.

Poop

is the space below an enclosed superstructure at the extreme aft end of a

ship.

Poop Deck

is the first deck above the shelter deck at aft end of a ship.

Port Light

is another term for side light or side scuttle.

Reduced Scantlings

are scantlings that are allowed to be reduced because

approved corrosion control arrangements have been applied.

Representative Spaces

is those which are expected to reflect the condition of

other spaces of similar type and service and with similar corrosion prevention

systems.

Scupper

is any opening for carrying off water from a deck, either directly or

through piping.

Scuttle

is 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

are slanted plates fitted in dry cargo holds to prevent undesired

pockets of cargo. The term is also commonly applied to slanted plates that are

fitted to improve the structural stability of corrugated bulkheads and framing

members.

Sheer Strake

is the top strake of a ship's side shell plating.

Single Bottom Structure

is the shell plating with stiffeners and girders below the

upper turn of bilge.

Skylight.

A deck opening fitted with or without glass port light and serving as a

ventilator for engine room, quarters, etc.

Spaces

are separate compartments including holds and tanks.

Stay

is a term for bulwarks and hatch coaming brackets.

Stem

is the piece of bar or plating at which a ship’s outside plating terminates at

her forward end.

Stern Frame

is the heavy strength member in single or triple screw ships,

combining the rudder post.

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Stiffener

is a collective term for secondary supporting structural members.

Stool

is a structure supporting cargo hold and tank bulkheads.

Strake

is a course, or row, of shell, deck, bulkhead, or other plating.

Strength Deck

is normally the uppermost continuous deck. After special

consideration of its effectiveness, another deck may be defined as strength deck.

Stringer Plate

is the outside strake of deck plating.

Superstructure

is a decked structure on the freeboard deck extending for at

least 92% of the breadth of the ship.

Suspect Areas

are locations showing substantial corrosion and/or which are

considered by the Surveyor to be prone to rapid wastage.

Tank Bulkhead

is a boundary bulkhead in a tank for liquid cargo, ballast or

bunkers.

Topside Wing Ballast

tanks are ballast tanks in bulk carriers that normally

stretch along the length of the ship’s side and occupy the upper corners of the

cargo hold.

Tween Decks

is an abbreviation of between decks, placed between the upper

deck and the tank top in the cargo holds.

Void

is an enclosed empty space in a ship.

Wash Bulkhead

is a perforated or partial bulkhead in a tank.

Watertight Bulkhead

is a collective term for transverse bulkheads required for

subdivision of the hull into watertight compartments.

Wind and Water Strakes

are the strakes of a ship's side shell plating between

the ballast and deepest load waterline.

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2.2 Nomenclature for typical hull structures

28

1 Strength deck plating 14 Bilge longitudinals

2 Stringer plate 15 Longitudinal bulkhead lower strake

3 Sheer strake 16 Side shell longitudinals

4 Side shell plating17 Longitudinal bulkhead plating

5 Bilge plating 18 Longitudinal bulkhead longitudinals

6 Bottom shell plating25 Deck transverse centre tank

7 Keel plate 26 Bottom transverse centre tank

8 Deck longitudinals 27 Deck transverse wing tank

9 Deck girders 28 Side shell vertical web

10 Sheer strake longitudinal 29 Longitudinal bulkhead vertical web

11 Longitudinal bulkhead top strake 30 Bottom transverse wing tank

12 Bottom longitudinals 31 Cross ties

13 Bottom girders 32 Transverse web face plate

Figure 1: Single Hull Tanker — Typical Transverse Section

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1 Strength deck plating 16 Side shell longitudinals

2 Stringer plate 17 Longitudinal bulkhead plating

3 Sheer strake 18 Longitudinal bulkhead longitudinals

4 Side shell plating19 Inner bottom plating

5 Bilge plating 20 Inner bottom longitudinals

6 Bottom shell plating25 Deck transverse centre tank

7 Keel plate 26 Bottom transverse centre tank

8 Deck longitudinals 27 Deck transverse wing tank

9 Deck girders 28 Side shell vertical web

10 Sheer strake longitudinal 29 Longitudinal bulkhead vertical web

11 Longitudinal bulkhead top strake

3. Hull Survey Terms

Abrasion

is the removal of material by mechanical, i.e. rubbing or frictional,

means.

Active Corrosion

means gradual chemical or electrochemical attack on a metal

producing loose scale, by atmosphere, moisture or other agents.

Allowable Corrosion

or

Wastage Limit

is the acceptable thickness diminution

of structural elements.

Anode

is the positively charged metal surface and the corroding part of an

electrochemical corrosion cell at which the oxidation or loss of electrons occurs.

Sacrificial anode or impressed current anode.

Antifouling

is paint for use on underwater areas on hulls. Antifouling contains

agents who prevent the adhesion and growth of organisms on the hull.

Bacterial Corrosion

or

Microbially Influenced Corrosion (MIC)

is corrosion

which is induced or accelerated by the presence of micro organisms.

Blasting

or

Shot-Blasting

is the cleaning of a metal surface by a stream of

abrasive particles.

Blister

- a raised area, often dome shaped, resulting from loss of adhesion

between a coating or deposit and the substrate.

Brittle Fracture

is the separation of a solid accompanied by little or no

macroscopic plastic deformation. Typically, brittle fracture occurs by rapid crack

propagation with less expenditure of energy than for ductile fracture. Brittle

tensile fractures have a bright, granular appearance and exhibit little or no

necking.

Buckling

: a bulge bend or other wavy condition of the structure caused by in

plane compressive stresses and /or shear stresses.

Butt Joint

is a joint between two structural members lying in the same plane.

Typically a butt joint is used to describe the welded connection between two

plates in the transverse direction.

Cathode

is the negatively charged metal surface and the non-corroding or

protected part of an electrochemical corrosion cell.

Cathodic Protection

is the partial or complete protection of a metal from

corrosion by making it a cathode, using either a galvanic or an impressed current

to bring a metal to a potential where it is thermodynamically stable.

Cavitation Damage

is degradation of metal surfaces, characterized by pitting, in

which the pit profile is irregular, occurring when very turbulent fluids are in

contact with the metal surface, and associated with the formation and collapse of

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cavities in the liquid at the solid — liquid interface.

Close-up Survey

is a survey where the details of structural members are within

the close visual inspection range of the surveyor, i.e. normally within the reach of

hand.

Coating Evaluation Criteria

is normally an assessment of the extent of damage

registered in terms of coating breakdown area and/or rust scales in % of area

under consideration, normally the complete tank, with additional information on

coating damage to edges and weld connection. Typical coating failures may be

given as additional information.

Coating,

often synonymous with

Painting

, i.e. a protective film of thickness

usually about 0,2 - 0,5 mm, applied to prevent corrosion mainly via a three main

mechanisms; the barrier effect, the cathodic effect or by inhibition / passivation.

Collision Damage

is damage caused by physical impact between two or more

ships used for navigation.

Condition Assessment Programme (CAP)

is a voluntary system, which gives a

detailed assessment of a tanker’ s actual condition at the time of inspection and is

available to both charter-parties and owners.

Condition Survey

is a survey normally of limited scope and time and intended to

identify any anticipated structural or corrosion related deficiencies and give an

overall visual impression of the structural integrity.

Contact Damage

is damage caused when the ship strikes something other than

another ship. (see also ‘

Grounding

’).

Corrosion Fatigue

is the process in which a metal fractures prematurely in a

trans-crystalline manner under conditions of simultaneous corrosion and

repeated cyclic loading of lower stress levels or fewer cycles than would be in the

absence of a corrosive environment

Corrosion

is the chemical or electrochemical reaction between a material,

usually a metal and its environment that produces a deterioration of material and

its properties, usually an oxide is formed.

Corrosion Prevention System

is considered a full hard coating; alternatively a

full hard coating supplemented by cathodic protection.

Crack

is a fracture type discontinuity without complete separation characterized

by a sharp tip and high ratio of length and width to opening displacement.

Crevice Corrosion

is localized corrosion of a metal surface at, or immediately

adjacent to, an area that is shielded from full exposure to the environment

because of close proximity between the metal and surface of another material.  It

is usually associated with small volumes of stagnant water; within lapped joints,

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under heads of fastenings, under gaskets and packings, under marine organisms

and porous deposits.

Critical Structural Areas

are locations which have been identified from

calculations to require monitoring or from the service history of the subject ship or

from similar ships to be sensitive to cracking, buckling or corrosion which would

impair the structural integrity of the ship.

Cumulative Damage

is an aggregation of damage due to various physical

causes, specifically applied to fatigue under various stress ranges and

frequencies.

Damage Survey

is a survey requested as a result of hull damage or other

defects.

Deformation

is a change in the form of a structure due to stress, thermal

change, change in moisture, or other causes.

Delamination

is peeling from undercoat or substrate.

Deposit Attack

is an attack under, or around, the edge of a local deposit formed

on a metal surface in the presence of an electrolyte.

Ductile Fracture

is

the separation of a solid accompanied by gross plastic

deformation.

Edge Corrosion

is local corrosion at the free edges of stiffeners, brackets,

flanges, manholes etc.

Elasticity

means the structural member's capability of sustaining stress without

permanent deformation, i.e. to recover its original size and shape after the stress

has been removed.

Electrochemical Corrosion

is corrosion associated with the passage of an

electric current. If the current is produced by the system itself it is called Galvanic

Corrosion and if it results from an impressed current it is called Electrolytic

Corrosion.

Erosion Corrosion

is a combined action involving corrosion and erosion in the

presence of a moving corrosive fluid, leading to the accelerated loss of material.

Erosion corrosion is characterized by grooves, gullies, waves, valleys etc.,

usually with directional pattern and with bright surfaces free from corrosion

products.

Erosion Damage

is the physical removal of material from a surface by

mechanical means such as e.g. flowing liquid and it may be accelerated by

corrosion.

Excessive Corrosion

is an extent of corrosion that exceeds the Allowable

Corrosion.

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Extensive Corrosion

is an extent of corrosion consisting of hard and/or loose

scale, including pitting, over 70% or more of the area under consideration,

accompanied by evidence of thickness diminution.

FAIR

condition

is a term used to describe the condition of a hard coating; with

local breakdown at edges of stiffeners and weld connections and/or light rusting

over 20% or more of areas under consideration, but less than as defined for

POOR condition.

Fair

is to smooth or fair up a ship's lines and eliminating irregularities.

Fatigue

is the phenomenon leading to fracture under repeated or fluctuating

stresses having a maximum value significantly less than the ultimate tensile

strength of the material.

Fracture

is the propagation of a crack through the thickness of a material.

( see ‘

Brittle

’ and ‘

Ductile

’ Fractures )

Galvanic Corrosion is

electrochemical accelerated corrosion of a metal

because of an electrical contact with a more noble metal or nonmetallic

conductor in a corrosive electrolyte.

Galvanizing

is the

deposition of zinc on to the surface of steel to provide

corrosion protection by both protecting the steel from contact with the

environment and giving sacrificial protection.

General Corrosion

or

Overall Corrosion

appears

as non-protective, friable rust

of a uniform nature on uncoated surfaces. Rust scale continually breaks off,

exposing fresh metal to corrosive attack. Visual judgment of thickness loss is

difficult until serious wastage has occurred.

GOOD

condition

is a term used to describe condition of hard coating; with only

minor spot rusting.

Grooving Corrosion

is local corrosion normally adjacent to welding joints along

abutting stiffeners and at stiffener or plate butts or seams.

Grounding

is contact of the ship’s bottom with the sea floor.

Hard Coating

is a coating which chemically converts during its curing process,

normally used for new construction, or non-convertible air drying coating which

may be used for maintenance purposes. Hard coating can be either organic or

inorganic and covers typical marine coatings such as those based on epoxy, coal

tar epoxy, polyurethane, chlorinated rubber, vinyl, zinc epoxy, zinc silicate.

Hose Testing

is carried out to demonstrate the tightness of structures not

subject to structural (hydrostatic) or leak testing and to other components that

contribute to the watertight or weathertight integrity of the hull.

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Hydropneumatic Testing

is a combination of hydrostatic and air testing.

Indent

is deformation of structural members caused by out of-plane loads like

bottom slamming and bow impact forces, contact with other objects etc.

Inhibitors

are substances used to prevent or retard a chemical or

electrochemical reaction, often used to render corrosion products less soluble

and thereby tending to stifle electrochemical corrosion processes.

Insignificant Corrosion

or

Minor Corrosion

is an extent of corrosion with minor

spot rusting and such that an assessment of the corrosion pattern indicates

wastage generally not exceeding of 30% of the allowable corrosion limits.

Lamination

is an excessively large, laminar, non-metallic inclusion, producing a

defect appearing in sheets or strips as segregation or in layers.

Lap Joint

is a joint between two structural members that overlap each other.

Leak Testing

is an air or other medium test carried out to demonstrate the

tightness of the structure.

Local Corrosion

is by name local in nature, often appearing at areas with local

breakdown of coating or at areas with stress concentrations.

Loose Scale

is sheets of rust falling off if the surveyor hits the structure with his

test hammer. Loose scale can best be removed by hand or power tool cleaning

or a combination of these.

Mill Scale

is thick oxide film formed on wrought-metal products which have been

hot-rolled or forged and allowed to cool in air, the term is principally applied to

steel on which the oxide is essentially magnetic black oxide.

Necking Effect

is a term describing local corrosion at junction of plating and

stiffeners due to flexure effects caused by reverse, cyclic loading with loss of

coating or shedding of scale exposing fresh steel to further corrosion. The

corrosion rate may be rather high and accelerates with thinning of the material.

On-hire/Off-hire Survey

is surveys carried out to state the ship's condition prior

to or after her chartering. The main purpose is to record deficiencies or damages.

Overall Survey

is survey intended to report on the overall condition of the hull

structure and determine the extent of additional close-up surveys.

Paint

can be

described as a liquid material capable of being applied or spread

over a solid surface on which it subsequently dries or hardens to form a

continuous adherent, obliterating film.

Paint Cracking

is deep cracks in paint that expose substrate.

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Periodical Survey

is a collective term of classification surveys carried out after

the delivery a ship and at prescribed time intervals, i.e. annual, intermediate and

renewal/special surveys.

Pinholing

is tiny, deep holes exposing substrate.

Pinpoint Rusting

is local rusting at pinholes or holidays.

Pitguard Anode

is a sacrificial anode placed just above tank bottom in order to

mitigate the general and pitting corrosion process.

Pitting Corrosion

is local, random scattered corrosion mainly on horizontal

surfaces and at structural details where water is trapped, particularly at bottom of

tanks. For coated areas the attack produces deep and small diameter pits which

may lead to perforation. Pitting of uncoated areas in tanks, as it progresses,

forms shallow but very wide scabby patches (e.g. 300 mm in diameter) and the

appearance resembles condition of general corrosion.

Plasticity

is the property of a material that allows it to be extensively repeatedly

deformed without rupture when acted upon by a force sufficient to cause

deformation and that allows it to retain its deformed shape after the applied force

has been removed.

POOR

condition is a term used to describe condition of hard coating; with

general breakdown of coating over 20% or more or hard scale at 10% or more of

areas under consideration.

Prompt and Thorough Repair

is permanent repair completed at the time of the

survey to the satisfaction of the surveyor, therein removing the need for

imposition of any associated condition of class.

Rust

is a visible corrosion product consisting of hydrated oxides of iron and is

formed on steel surfaces exposed to moist atmospheric conditions.

Sags

are excess flow of paint, also called runs or curtains.

Scale

is surface oxidation, consisting of partially adherent layers of corrosion

products, left on metals by heating or casting in air or in other oxidizing

atmospheres and is the product of the corrosion process of steel with a porous

surface layer or flakes, in volume greater than the metal from which it was

formed.

Scantlings

are the dimensions of a ship's structural members as girders,

stiffeners and plates.

Seam

is a joint between two structural members lying in the same plane.

Typically a seam is used to describe the welded connection of two plates in the

longitudinal direction.

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Semi-hard Coating

is a coating that dries or converts in such a way that it stays

flexible although hard enough to touch and walk upon.

Shop primer

is a rust preventing paint for temporary protection of steel

immediately after blasting for protection of the material surface from corrosion

during construction and until the final paint system is applied.

Soft Coating

is a coating that remains soft so that it wears off at low mechanical

impact or when touched; often based on oils (vegetable or petroleum) or lanolin

(sheep wool grease). Application of soft coating does generally not allow

relaxation of the extent of periodical hull survey requirements of ballast tanks.

Statutory Survey

is a collective term of surveys required to meet International

Convention requirements such as Load Line, SOLAS and MARPOL.

Strain

is any forced change in the dimensions of a structural member.

Stress Concentration

or

Stress Raiser

is a term used of any notch, crack, hole,

corner, groove, attachment or other interruption to smooth flow of stress and

strain in structures introduces a concentration of stress.

Stress Corrosion

is the preferential attack of areas under tensile stress in a

corrosive environment, where such an environment alone would not have caused

corrosion. Tensile stresses may be residual stresses from welding or cold-

working or applied working stresses.

Stripe Coating

is used to produce a coating with sufficient film thickness on

edges, corners, weld seams and other areas that are difficult to coat using airless

spray.

Structural Testing

or

Tank Testing

is a hydrostatic test carried out to

demonstrate the structural adequacy of design and tightness of tank boundaries.

Substantial Corrosion

is an extent of corrosion such that assessment of

corrosion pattern indicates wastage in excess of 75% of allowable corrosion, but

within allowable corrosion limits.

Survey

is a collective term for examination, testing and evaluation of results and

decision making.

Suspect Areas

are locations showing substantial corrosion and/or are

considered to be prone to rapid wastage.

Transverse Section

includes, for thickness measurement purposes, all

longitudinal members such as plating, longitudinals and girders at the deck, side,

bottom, inner bottom and longitudinal bulkheads. For transversely framed ships,

a transverse section includes adjacent frames and their end connections in way

of transverse section. Also called

Girthbelt.

Watertight

means capable of preventing the passage of water through the

structure under a head of water for which the surrounding structure is designed.

Wear

is the deterioration of a surface due to relative motion between it and

another.

Weathertight

means

that in any sea condition water will not penetrate into the

ship.

Weld Metal Corrosion

is a preferential corrosion of the weld deposit due to an

electrolytic action between the weld metal and base metal.