A B and C Class Divisions

'A' class divisions are constructed of steel or equivalent material and are to be capable of preventing the passage of smoke and flame to the end of a one-hour standard fire test. A plain stiffened steel bulkhead or deck has what is known as an A-O rating. By adding insulation in the form of approved incombustible materials to the steel an increased time is taken for the average temperature of the unexposed side to rise to 139 C above the original temperature or not more than 180 C at any one...

Fore End Structure

Consideration is given in this chapter to the structure forward of the collision bulkhead. The chain locker is included as it is usually fitted forward of the collision bulkhead below the second deck or upper deck, or in the forecastle itself. An overall view of the fore end structure is shown in Figure 20.1, and it can be seen that the panting stiffening arrangements are of particular importance. These have already been dealt with in detail in Chapter 17 as they are closely associated with the...

Structural Design Programs

In recent years the principal classification societies have developed software packages for use by shipyards which incorporate dynamic-based criteria for the scantlings, structural arrangements and details of ship structures. This was a response to a perception that the traditional semi-empirical published classification rules based on experience could be inadequate for new and larger vessel trends. The computer programs made available to shipyards incorporate a realistic representation of the...

Purchase of a New Vessel

In recent years the practice of owners commissioning 'one off' designs for cargo ships from consultant naval architects, shipyards or their own technical staff has increasingly given way to the selection of an appropriate 'stock design' to suit their particular needs. To determine which stock design, the shipowner must undertake a detailed project analysis involving consideration of the proposed market, route, port facilities, competition, political and labour factors, and cash flow...

Protection of Special Category Spaces

A special category space is an enclosed space above or below the bulkhead deck used for the carriage of motor vehicles with fuel for their own propulsion in their own tanks and to which passengers have access. Obvious examples are the garage spaces in ro-ro passenger ferries and vehicle decks in ro-ro cargo ships. Such spaces cannot have the normal main vertical fire zoning without interfering with the working of the ship. Equivalent protection is provided in such spaces by ensuring that the...

Liquefied Natural Gas ships

There are over twenty approved patent designs of containment vessel for LNG ships, the majority of which fall into the membrane or independent tank categories. Those types which have been or are more commonly found in service are described below. A feature of LNG ships is their double hull construction within which are fitted the cargo tanks and the secondary barrier system. INDEPENDENT TYPE A TANKS Early LNG ships such as the 'Methane Princess' and 'Methane Progress' were fitted with...

Prfabrication

During the Second World War a large number of merchant and war ships were required to be built in a short period of time. These requirements speeded the adoption of welding in shipyards, and often led to the application of mass production techniques in shipbuilding. Prefabrication of ship units, that is the construction of individual sections of the ship's structure prior to erection, became a highly developed science. Often the units were manufactured at a location remote from the shipyard,...

Aluminium Alloy

There are three advantages which aluminium alloys have over mild steel in the construction of ships. Firstly aluminium is lighter than mild steel (approximate weights being aluminium 2.723 tonnes m3, mild steel 7.84 tonnes m3), and with an aluminium structure it has been suggested that up to 60 per cent of the weight of a steel structure may be saved. This is in fact the principal advantage as far as merchant ships are concerned, the other two advantages of aluminium being a high resistance to...

Air and Sounding Pipes

Air pipes are provided for all tanks to prevent air being trapped under pressure in the tank when it is filled, or a vacuum being created when it is emptied. The air pipes may be fitted at the opposite end of the tank to the filling pipe and or at the highest point of the tank. Each air pipe from a double bottom tank, deep tanks which extend to the ship's side, or any tank which may be run up from the sea, is led up above the bulkhead deck. From oil fuel and cargo oil tanks, cofferdams, and all...

Classification Society Weld Tests

Classification societies specify a number of destructive tests which are intended to be used for initial electrode and weld material approval. These tests are carried out to ascertain whether the electrode or wire-flux combination submitted is suitable for shipbuilding purposes in the category specified by the manufacturer. Tests are made for conventional electrodes, deep penetration electrodes, wire-gas and wire-flux combinations, consumables for electro-slag and electro-gas welding, and...

Protection by Means of Paints

It is often assumed that all paint coatings prevent attack on the metal covered simply by excluding the corrosive agency, whether air or water. This is often the main and sometimes the only form of protection however there are many paints which afford protection even though they present a porous surface or contain various discontinuities. For example certain pigments in paints confer protection on steel even where it is exposed at a discontinuity. if the reactions at the anode and cathode of...

Periodical Surveys

To maintain the assigned class the vessel has to be examined by the Society's surveyors at regular periods. The major hull items to be examined at these surveys only are indicated below. annual surveys All steel ships are required to be surveyed at intervals of approximately one year. These annual surveys are where practicable held concurrently with statutory annual or other load line surveys. At the survey the surveyor is to examine the condition of all closing appliances covered by the...

Plate and Section Preparation

Initial preparation of material is essential for its efficiency in the completed ship structure and its marshalling on arrival is essential to the efficiency of the shipbuilding process. STOCKYARD On arrival at the shipyard, plates and sections are temporarily stored in the stockyard. As a rule the stockyard is an uncovered space having sufficient area to provide storage for enough plates and sections required for the working of the yard some months ahead. In the United Kingdom the amount...

Other Welding Processes

Thermit Welding Process

There are one or two welding processes which cannot strictly be classified as gas or arc welding processes and these are considered separately. electro-slag welding The electro-slag welding process may be used for the automatic vertical welding of thicker steel plate. It is claimed that the welding of plates of thickness down to 13 mm can be economical, but it is usual to weld somewhat heavier plates with this process. Heavy cast sections up to 450 mm in thickness can in fact be welded. To...

Conditions of Assignment of Freeboard

(1) The construction of the ship must be such that her general structural strength will be sufficient for the freeboards to be assigned. The design and construction of the ship must be such that her stability in all probable loading conditions is sufficient for the freeboards assigned. Stability criteria are given in the Convention. (2) Superstructure End Bulkheads To be of efficient construction to the satisfaction of the Administration. The heights of the sills of openings at the ends of...

Heat Treatment of Steels

The properties of steels may be altered greatly by the heat treatment to which the steel is subsequently subjected. These heat treatments bring about a change in the mechanical properties principally by modifying the steel's structure. Those heat treatments which concern shipbuilding materials are described. annealing This consists of heating the steel at a slow rate to a temperature of say 850 C to 950 C, and then cooling it in the furnace at a very slow rate. The objects of annealing are to...

Production of Aluminium

For aluminium production at the present time the ore, bauxite, is mined containing roughly 56 per cent aluminium. The actual extraction of the aluminium from the ore is a complicated and costly process involving two distinct stages. Firstly the bauxite is purified to obtain pure aluminium oxide known as alumina the alumina is then reduced to a metallic aluminium. The metal is cast in pig or ingot forms and alloys are added where required before the metal is cast into billets or slabs for...

Electric Arc Welding

The basic principle of electric arc welding is that a wire or electrode is connected to a source of electrical supply with a return lead to the plates to be welded. If the electrode is brought into contact with the plates an electric current flows in the circuit. By removing the electrode a short distance from the plate, so that the electric current is able to jump the gap, a high temperature electrical arc is created. This will melt the plate edges and the end of the electrode if this is of...

Liquefied Petroleum Gas Ships

Ships carrying LpG are categorized by their cargo containment system. fully pressurized tanks The capacity of fully pressurized ships is usually less than 2000 m3 of propane, butane or anhydrous ammonia carried in two to six uninsulated horizontal cylindrical pressure vessels arranged below or partly below deck. These independent tanks of Type c are normally designed for working pressures up to 17.5 kg cm2 which Cargo temperature 10 C and at atmospheric above pressure Below 10 C Below 55' Down...

Bilge and Ballast Pumping and Piping

All cargo ships are provided with pumping and piping arrangements so that any watertight compartment or watertight section of a compartment can be pumped out when the vessel has a list of up to 5 , and is on an even keel. In the case of passenger ships, each compartment or section of a compartment may be pumped out following a casualty under all practical conditions whether the ship is listed or not. The arrangements in the machinery space are such that this space may be pumped out through two...

Welding Sequences

During the welding operation heat is applied to the plate, and because of this the metal will expand, and on cooling contract. A weld on cooling and contracting tends to pull the plate with it. This results in a structural deflection, the restraining action of the plate preventing the weld from contracting fully. The actual distortion of a welded structure is difficult to predict owing to the lack of knowledge of the degree of restraint. It is known however that shrinkage in butt welds does...

Derrick Rigs

Ships Derricks

Various forms of derrick rig may be used aboard the cargo ship, the commonest use of the single derrick being as a 'single swinging derrick' (see Figure 24.2(a)). Adjacent derrick booms may be used in 'union purchase' (Figure 24.2(b)) the booms being fixed in the overboard and inboard positions. Cargo is lifted from the hatch and swung outboard by the operator Figure 24.1 Stiffening in way of mast and heavy derrick Figure 24.1 Stiffening in way of mast and heavy derrick controlling the winches...

Loftwork Following Drawing Office

The mould loft in a shipyard was traditionally a large covered wooden floor area suitable for laying off ship details at full size. When the loftsmen received the scale lines plan, and offsets from the drawing office, using the traditional method the lines would be laid off full size and faired. This would mean using a great length of floor even though a contracted sheer and plan were normally drawn, and aft and forward body lines were laid over one another. Body sections were laid out full...

Freeboard Computation

Basic freeboards are given in the rules which are dependent on the length and type of vessel. Ships are divided into types 'A' and 'B'. Type 'A' ships are those which are designed to carry only liquid cargoes in bulk, and in which the cargo tanks have only small access openings closed by watertight gasketed covers of steel or equivalent material. These vessels benefit from the minimum assignable freeboard. All ships which do not come within the provisions regarding Type 'A' ships are considered...

Plate and Section Machining

Line Bending Steel Plate

A number of the methods in use for forming plates into the required shapes are time honoured. This is particularly true of the methods adopted for fitting plates to the curve of the hull, but as we have seen in the previous chapter the information for doing this can now be derived using the CAD CAM systems available. Cutting flat plates to the required profiles has in the past decade become highly automated, very sophisticated machine tools having been introduced for this purpose. In the main,...

Oil Tankers

Bulk Carrier Structure

Until 1990 the form of vessels specifically designed for the carriage of oil cargoes had not undergone a great deal of change since 1880 when the vessel illustrated in Figure 3.5(a) was constructed. The expansion tank and double bottom within the cargo space having been eliminated. The greatest changes in that period were the growth in ship size and nature of the structure (see Figure 3.5(b)). The growth in size of ocean-going vessels from 1880 to the end of the Second World War was gradual,...

Superstructures and Deckhouses

Superstructures might be defined as those erections above the freeboard deck which extend to the ship's side or almost to the side. Deckhouses are those erections on deck which are well within the line of the ship's side. Both structures are of importance in the assignment of the load line as they provide protection for the openings through the freeboard deck. Of particular importance in this respect are the end bulkheads of the superstructures, particularly the bridge front which is to...

Nature and Forms of Corrosion

There is a natural tendency for nearly all metals to react with their environment. The result of this reaction is the creation of a corrosion product which is generally a substance of very similar chemical composition to the original mineral from which the metal was produced. atmospheric corrosion Protection against atmospheric corrosion is important during the construction of a ship, both on the building berth and in the shops. Serious rusting may occur where the relative humidity is above...

Fabrication Of Large Aluminium Panels By Mechanised Mig Welding

Allday, 'Fabrication of Large Aluminium Panels by Mechanised MIG Welding', Lightweight Materials in Naval Architecture 1996, Royal Institution of Naval Architects Publications. 'Automatic Vertical Welding on the Berth', The Naval Architect, April, 1971. Chadburn and Salter, 'The Welding of Higher Tensile Shipbuilding Steels', The Naval Architect, January, 1974. Gilbert and Maughan, 'Economics of Welding from One Side', Shipping World and Shipbuilder, September, 1968. Gourd, 'Principles of...

Bulwarks

Bulwarks fitted on weather decks are provided as protection for personnel and are not intended as a major structural feature. They are therefore of light scantlings, and their connections to the adjacent structures are of some importance if high stresses in the bulkwarks are to be avoided. Freeing ports are cut in bulwarks forming wells on decks in order that water may Section through cross joint between panels Dumb panel raised by high-lift cylinders c WEATHER TIGHT GASKETS FOR Motorized panel...

Joining Ship Sections Afloat

Owing to the enormous increase in size of bulk carriers and tankers, shipyards with restricted facilities, berth size particularly, have examined various means of building these large ships in sections which are to be joined off the berth. In most cases the problem becomes one of joining the two hull sections afloat or in a dry-dock of sufficient size where available. Where the sections are to be joined afloat extremely accurate fit up of the sections is aided by the possibilities of ballasting...

Corrosion Control

The prevention of corrosion may be broadly considered in two forms, cathodic protection and the application of protective coatings. CATHODIC PROTECTION Only where metals are immersed in an electrolyte can the possible onset of corrosion be prevented by cathodic protection. The fundamental principle of cathodic protection is that the anodic corrosion reactions are suppressed by the application of an opposing current. This superimposed direct electric current enters the metal at every point...

Unit Erection

When any panel and the block assemblies are complete there will be some time buffer before their erection at the building berth or dock to allow for mishaps in the production schedule. Stowage is generally adjacent to the building hall and will vary in size according to the yard's practice, some yards storing a large number of units before transferring them to the berth or dock for erection in order to cut the berth dock time to a minimum. Sequences of erection for any particular ship vary from...

Further Reading

Eidal, 'Recent Developments in Fire Safety for High Speed Craft,' Fire at Sea 1997, Royal Institution of Naval Architects Publications. Hoyning and Taby, 'Fire Protection of Composite Vessels Fire Protection and Structural Integrity an Integrated Approach', Fire at Sea 1997, Royal Institution of Naval Architects Publications. IMO 'International Code of Safety for High Speed Craft HSC Code ' 1994. Marchant, 'Meeting the Fire Requirements of the IMO High Speed Craft Code with Composite...

Stern and Bow Doors

Ro-ro vessels may be fitted with stern doors of the hinge down or hinge up type which if large are articulated. Bow doors are either of the visor type or of the side hinged type 'barn door' type . These are situated above the freeboard deck and where the bow doors lead to a complete or long forward enclosed superstructure Lloyd's require an inner door to be fitted which is part of the collision bulkhead. This would also be in keeping with the SOLAS requirements for passenger ships where the...

Stem Construction Of Ship

On many conventional ships a stem bar, which is a solid round bar, is fitted from the keel to the waterline region, and a radiused plate is fitted above the waterline to form the upper part of the stem. This forms what is referred to as a 'soft nose' stem, which in the event of a collision will buckle under load, keeping the impact damage to a minimum. Older ships had solid bar stems which were riveted and of square section, and as the stem had no rake it could cause considerable damage on...

Propellers

Ship propellers may have from three to six similar blades, the number being consistent with the design requirements. It is important that the propeller is adequately immersed at the service drafts and that there are good clearances between its working diameter and the surrounding hull structure. The bore of the propeller boss is tapered to fit the tail shaft and the propeller may be keyed onto this shaft a large locking nut is then fitted to secure the propeller on the shaft. For securing the...

Welding Practice

Automatic Welding Slag Chipping System

In making a butt weld with manual arc welding, where the plate thickness exceeds say 5 to 6 mm it will become necessary to make more than one welding pass to deposit sufficient weld metal to close the joint. With the higher current automatic welding processes thicker plates may be welded with a single pass, but at greater thicknesses multi-pass welds become necessary. In ship work unless a permanent backing bar is used, or the 'one sided' welding technique Chapter 9, Submerged Arc Welding is...

Frame Bending

The traditional system of bending side frames may still be in use for repair work, and is described as follows. A 'set-bar' which is a flat bar of soft iron is bent to the scrieve line of the frame on the scrieve board and then taken to the frame bending slabs. On these solid cast-iron slabs pierced with holes the line of the frame is marked, and modified to agree with the line of the toe of the frame. As the heated frame on cooling will tend to bend, the set-bar is sprung to allow for this...

Bulbous Bows

Vessels operating at higher speeds, and those with high block coefficients, are often found to have a bulbous or protruding bow below the waterline. The arguments for and against fitting some form of bulbous bow are the province of text-books on naval architecture, but it may be indicated that like most peculiarities of the immersed hull form this feature is usually intended to reduce the vessel's resistance to motion under certain conditions. From the construction point of view the bulbous bow...

Shaft Bossing and A Brackets

Propeller Bossing

Twin-screw or multi-screw vessels have propeller shafts which leave the line of shell at some distance forward of the stern. To support the shaft overhang, bossings or 'A' brackets may be fitted. Bossings are a common feature on the larger multiple-screw passenger ships and are in effect a moulding of the shell which takes in the line of shaft for some distance. Access from inside the hull is thus provided to the shaft over a great proportion of its length, and it is afforded greater...

Ship Construction Pillars

Tripping Bracket

Heavy plate introduced into deck girder flange in way of pillar intersection in the double bottom below. Where this is not possible partial floors and short intercostal side girders may be fitted to distribute the load. Machinery space pillars are fabricated from angles, channels, or rolled steel joists, and are heavily bracketed to suitably stiffened members Figure 18.6 . SMALL PILLARS Within the accommodation and in relatively small vessels solid round steel pillars having diameters seldom...

Refrigerated Container Ships

Many of the container ships operating on trade routes where refrigerated cargoes were carried in conventional refrigerated cargo liners 'reefer ships' have provision for carrying refrigerated containers and have in many cases replaced the latter. The ISO containers usually 20 foot size since with most refrigerated cargoes 40 foot size would be too heavy are insulated, and below decks the end of each hold may be fitted with brine coolers which serve each stack of containers. Air from the brine...

Gussac Plate Ship Construction

Hatchway Coaming Deep Webs

The weather decks of ships are cambered, the camber being parabolic or straight. There may be advantages in fitting horizontal decks in some ships, particularly if containers are carried and regular cross-sections are desired. Short lengths of internal deck or flats are as a rule horizontal. Decks are arranged in plate panels with transverse or longitudinal stiffening, and local stiffening in way of any openings. Longitudinal deck girders may support the transverse framing, and deep transverses...

Pillars

The prime function of the pillars is to carry the load of the decks and weights upon the decks vertically down to the ship's bottom structure where these loads are supported by the upward buoyant forces. A secondary function of pillars is to tie together the structure in a vertical direction. Within the main hull of a cargo ship two different forms of pillar may be found, those in the holds invariably fulfilling the first function, and those in the machinery spaces fulfilling the latter...

Rudders

Dimensions Ship Rudder

Many of the rudders which are found on present-day ships are semibalanced, i.e. they have a small proportion of their lateral area forward of the turning axis less than 20 per cent . Balanced rudders with a larger area forward of the axis 25 to 30 per cent , and un-balanced rudders with the full area aft of the axis are also fitted. The object of balance is to achieve a reduction in torque since the centre of lateral pressure is brought nearer the turning axis. However the fully balanced rudder...

Outfit Modules

Units of machinery, pipework and other outfit systems required for a specific zone can be planned and built up into modules and installed as such into a block fabrication. Pipework in particular lends itself to this form of assembly and can, with careful planning from the CAD stage, be arranged in groupings so that pipe bank modules can be arranged for a particular zone. Modules can range from a small pipe bank supported by light framing of pipe hangers, or a complete auxiliary machinery unit...

Classification Society Tests for Hull Materials

Charpy Impact Machine

Both mild steel and higher tensile steel plates and sections built into a ship are to be produced at works approved by the appropriate classification society. During production an analysis of the material is required and so are prescribed tests of the rolled metal. Similar analyses and tests are required by the classification societies for steel forgings and steel castings, in order to maintain an approved quality. Destructive tests are made on specimens obtained from the same product as the...

Shell Plating

Ship Construction Shell Plating

The bottom and side shell plating consists of a series of flat and curved steel plates generally of greater length than breadth butt welded together. The vertical welded joints are referred to as 'butts' and the horizontal welded joints as 'seams' see Figure 17.1 . Stiffening members both longitudinal and transverse are generally welded to the shell by intermittent fillet welds with a length of continuous weld at the ends of the stiffening member. Continuous welding of stiffening members to the...

Cargo Restraint

Cell Guides

In ro-ro and container ships the lashing of cargo is an important safety consideration and usually calls for fittings which will permit rapid and easy but effective securing of the cargo because of short ship turn around times. The shipbuilder is responsible for the deck and perhaps hatch fittings for the securing devices and will look to the ship operator for guidance on their type and positions. On the decks of ro-ro ships where the direction of lashing is unpredictable and vehicles must...

Steering Gear

Rudder Carrier Bearing

Unless the main steering gear comprises two or more identical power units, every ship is to be provided with a main steering gear and an auxiliary steering gear. The main steering gear is to be capable of putting the rudder over from 35 on one side to 35 on the other side with the ship at its deepest draft and running ahead at maximum service speed, and under the same conditions from 35 on either side to 30 on the other side in not more than 28 seconds. It is to be power operated where...

Bending Moments in a Seaway

When a ship is in a seaway the waves with their troughs and crests produce a greater variation in the buoyant forces and therefore can increase the Figure 8.1 Vertical shear and longitudinal bending in still water bending moment, vertical shear force, and stresses. Classically the extreme effects can be illustrated with the vessel balanced on a wave of length equal to that of the ship. If the crest of the wave is amidships the buoyancy forces will tend to 'hog' the vessel if the trough is...

Single Bottom Structure

In smaller ships having single bottoms the vertical plate open floors are fitted at every frame space and are stiffened at their upper edge. A centre line girder is fitted and one side girder is fitted each side of the centre line where the beam is less than 10 m. Where the beam is between 10 and 17 m two side girders are fitted and if any bottom shell panel has a width to length ratio greater than four additional continuous or intercostal stiffeners are fitted. The continuous centre and...

Testing of Materials

Metals are tested to ensure that their strength, ductility, and toughness are suitable for the function they are required to perform. In comparing the strengths of various metals stresses and strains are often referred to and require to be defined. Stress is a measure of the ability of a material to transmit a load, and the intensity of stress in the material, which is the load per unit area, is often stated. The load per unit area is simply obtained by dividing the applied load by the...

Bilge Keel

Midship Section Container

Most ships are fitted with some form of bilge keel the prime function of which is to help damp the rolling motion of the vessel. Other relatively Rounded sheerstrake . m grade 'E' Deck plating Rounded sheerstrake . m grade 'E' Deck plating Bottom plating 14mm Bottom longitudinals 225mm x 11mm O.B.P Figure 17.7 Bulk carrier midship section Bottom plating 14mm Bottom longitudinals 225mm x 11mm O.B.P Figure 17.7 Bulk carrier midship section minor advantages of the bilge keel are protection for the...

End Launches

Stern Launching Cradle

On release of a holding mechanism the launching cradle with the ship slides down the ground ways under the action of gravity. When the stern has entered the water the vessel is partly supported by buoyancy and partly by the ground ways. If this buoyancy is inadequate after the centre of gravity of the ship has passed the way ends, the ship may tip about the way ends causing large pressures on the bottom shell and on the ends of the ground ways. To avoid this the greatest depth of water over the...

Deep Tanks

Tripping Brackets

Deep tanks were often fitted adjacent to the machinery spaces amidships to provide ballast capacity, improving the draft with little trim, when the ship was light. These tanks were frequently used for carrying general cargoes, and also utilized to carry specialist liquid cargoes. In cargo liners where the carriage of certain liquid cargoes is common practice it was often an advantage to have the deep tanks adjacent to the machinery space for cargo heating purposes. However in modern cargo...

Ramps

Ro-ro ships fitted with ramps usually have a stern ramp, but some vessels fitted with bow doors may also have a bow ramp which doubles as the inner weathertight door see above and is lowered onto a linkspan when the bow visor or side hinged doors have been opened. Ramps may also be fitted internally to give access from deck to deck. These can be hydraulically or mechanically tilted to serve more than one deck and can be fixed in the horizontal position to serve as decks themselves see Figure...

Gas Welding

Forward Gas Welding Techniques

A gas flame was probably the first form of heat source to be used for fusion welding, and a variety of fuel gases with oxygen have been used to produce a high temperature flame. The most commonly used gas in use is acetylene which gives an intense concentrated flame average temperature 3000 C when burnt in oxygen. An oxy-acetylene flame has two distinct regions, an inner cone, in which the oxygen for combustion is supplied via the torch, and a surrounding envelope in which some or all the...

Cutting Processes

Steel plates and sections were mostly cut to shape in shipyards using a gas cutting technique, but the introduction of competitive plasma-arc cutting machines has led to their widespread use in shipyards today. GAS CUTTING Gas cutting is achieved by what is basically a chemical thermal reaction occurring with iron and iron alloys only. Iron or its alloys may be heated to a temperature at which the iron will rapidly oxidize in an atmosphere of high purity oxygen. The principle of the process as...

Flat Plate Keel

At the centre line of the bottom structure is located the keel, which is often said to form the backbone of the ship. This contributes substantially to the longitudinal strength and effectively distributes local loading caused when docking the ship. The commonest form of keel is that known as the 'flat plate' keel, and this is fitted in the majority of ocean-going and other vessels see Figure 16.1 a . A form of keel found on smaller vessels is the bar keel Figure 16.1 b . The bar keel may be...

Framing

Transverse Ships

The bottom shell may be transversely or longitudinally framed, longitudinal framing being preferred particularly for vessels exceeding 120 m in length. The side shell framing may also be transversely or longitudinally framed, transverse framing being adopted in many conventional cargo ships, particularly where the maximum bale capacity is required. Bale capacities are often considerably reduced where deep transverses are fitted to support longitudinal framing. Longitudinal framing may be...

Bulkheads

Bulkhead spacing throughout the cargo tank space is determined by the permissible length of cargo tanks. MARPOL requires that the length of each cargo tank shall not exceed the greater of 10 metres or a length expressed as a percentage of the ship's length which is dependent on the number of longitudinal bulkheads fitted and the minimum distance from the ship's side of the outer longitudinal bulkhead. Tankers with two or more longitudinal bulkheads may have wing and centre tank lengths up to 20...

Double Bottom Structure

Transverse Framing Ship Construction

An inner bottom or tank top may be provided at a minimum height above the bottom shell, and maintained watertight to the bilges. This provides a considerable margin of safety, since in the event of bottom shell damage only the double bottom space may be flooded. The space is not wasted but utilized to carry oil fuel and fresh water required for the ship, as well as providing ballast capacity. The minimum depth of the double bottom in a ship will depend on the classification society's...

Construction in Tank Spaces

Deep Web Frame Tanker

Ocean-going tankers have a longitudinally framed bottom shell and deck through the tank spaces. The side shell may however be either longitudinally framed or transversely framed, and the longitudinal bulkheads longitudinally or vertically stiffened in other than the larger tankers. Lloyd's Register generally requires full longitudinal framing once the vessel's length exceeds 150 m. transverse side framing Where transverse framing is adopted in smaller and medium size tankers the frames are...

Local Strengthening of Shell Plating

Ship Shell Plating

The major region in which the shell plating is subjected to local forces at sea is at the forward end. Strengthening of the forward bottom shell for Figure 17.3 Web frame and tank side bracket Figure 17.3 Web frame and tank side bracket pounding forces is dealt with in Chapter 16. Panting which is discussed in Chapter 8 will also influence the requirements for the scantlings and strengthening of the shell forward and to a lesser extent at the aft end. Where a ship is to navigate in ice a...

The IMO International Gas Carrier Code

In 1975 the 9th Assembly of IMO adopted the Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk, A.328 IX which provides international standards for ships which transport liquefied gases in bulk. It became mandatory in 1986 and is generally referred to as the IMO International Gas Carrier Code. The requirements of this code are incorporated in the rules for ships carrying liquefied gases published by Lloyd's and other classification societies. The code covers...

Brittle Fracture

With the large-scale introduction of welding in ship construction much consideration has been given to the correct selection of materials and structural design to prevent the possibility of brittle fracture occurring. During the Second World War the incidence of this phenomenon was high amongst tonnage hastily constructed, whilst little was known about the mechanics of brittle fracture. Although instances of brittle fracture were recorded in riveted ships the consequences were more disastrous...

Stern Construction

As the cruiser stern overhang may be subjected to large slamming forces a substantial construction with adequate stiffening is required. Solid floors are fitted at every frame space, and a heavy centre line girder is fitted right aft at the shell and decks. The stern plating is stiffened by cant frames or webs with short cant beams supporting the decks and led to the adjacent heavy transverse deck beam. Further stiffening of the plating is provided, or adopted in lieu of cant frames, by...

Insulation

As the steel hull structure is an excellent conductor of heat, some form of insulation must be provided at the boundaries of the refrigerated compartments if the desired temperatures are to be maintained economically. Cork, glass fibre, and various foam plastics in sheet or granulated form may be used for insulating purposes, also air spaces which are less efficient. Figure 28.2 Midship section of refrigerated cargo ship Figure 28.2 Midship section of refrigerated cargo ship Glass fibre is...

Aft End Structure

Considerable attention is paid to the overall design of the stern in order to improve flow into and away from the propeller. The cruiser stern see Figure 21.1 was for many years the favoured stern type for ocean going ships, but today most of these vessels have a transom stern see Figure 21.2 . A cruiser stern presents a more pleasant profile and is hydrodynamically efficient, but the transom stern offers a greater deck area aft, is a simpler construction, and can also provide improved flow...

Shipbuilding Steels

Steel for hull construction purposes is usually mild steel containing 0.15 per cent to 0.23 per cent carbon, and a reasonably high manganese content. Both sulphur and phosphorus in the mild steel are kept to a minimum less than 0.05 per cent . Higher contents of both are detrimental to the welding properties of the steel, and cracks can develop during the rolling process if the sulphur content is high. Steel for a ship classed with Lloyd's Register is produced by an approved manufacturer, and...

Side Doors and Loaders

Side door ramps are available for ro-ro operations and are similar to stern door ramp installations. Most side door installations, however, are intended for quayside fork lift operations with palletized cargo being loaded onto a platform at the door by the quayside forklift and stowed in the ship by another forklift truck. Instead of a loading platform on ships trading to ports with high tidal ranges a ramp onto which the quayside forklift truck drives may be fitted. Elevator platforms may be...

Watertight Doors

In order to maintain the efficiency of a watertight bulkhead it is desirable that it remains intact. However in some instances it becomes necessary to provide access between compartments on either side of a watertight bulkhead and watertight doors are fitted for this purpose. A particular example of this in cargo ships is the direct means of access required between the engine room and the shaft tunnel. in passenger ships watertight doors are more frequently found where they allow passengers to...

International Convention on Tonnage Measurement of Ships 1969

An International Conference on Tonnage Measurement was convened by IMO in 1969 with the intention of producing a universally acceptable system of tonnage measurement. The International Convention on Tonnage Measurement of Ships 1969 was prepared at this conference and this convention came into force on the 8th July, 1982. All ships constructed on or after that date were measured for tonnage in accordance with the 1969 Convention. Ships built prior to that date were if the owner so desired...

Ventilation

In most ships a combination of natural and mechanical ventilation is provided in the accommodation and machinery spaces. Mechanical supply is common, and a natural exhaust may be permitted in a number of compartments but where fumes, etc., are present, for example from galleys, a mechanical exhaust is required. This is also the case with many public rooms, often crowded and where smoking is permitted. The mechanical supply is by means of light steel sheet trunking, with louvres at each outlet....

Chain Locker

A chain locker is often arranged in the position forward of the collision bulkhead shown in Figure 20.1, below either the main deck or the second deck. It can also be fitted in the forecastle or aft of the collision bulkhead, in which case it must be watertight and have proper means of drainage. Chain locker dimensions are determined in relation to the length and size of cable, the depth being such that the cable is easily stowed, and a direct lead at all times is provided to the mouth of the...

Portable Decks

Portable decks are fitted in a variety of ships permitting flexibility of stowage arrangements and allowing totally different cargoes to be carried on different voyages. An extreme example is a 50 000 tonne deadweight bulk carrier fitted with hoistable car decks stowed under the hold wing tanks when taking ore from Australia to Japan and lowered for the return voyage when 3000 cars are carried. The car deck is the most common form of portable deck and common in ro-ro ferries. Hoistable decks...

Ship Drawing Offices and Loftwork

Shell Expansion Plan Ship

The ship drawing office is traditionally responsible for producing detailed working structural and general arrangement drawings for parts of the hull and outfit. Structural drawings prepared by the drawing office will be in accordance with Lloyd's or other classification rules and subject to their approval also owner's additional requirements and standard shipyard practices are incorporated in the drawings. General arrangements of all the accommodation and cargo spaces and stores are prepared,...

Welding and Cutting Processes used in Shipbuilding

Initially welding was used in ships as a means of repairing various metal parts. During the First World War various authorities connected with shipbuilding, including Lloyd's Register, undertook research into welding and in some cases prototype welded structures were built. However, riveting remained the predominant method employed for joining ship plates and sections until the time of the Second World War. During and after this war the use and development of welding for shipbuilding purposes...

Shipyard Layout

Most shipyards are well established and were originally sited in a suitable location for building small ships with methods which have now been superseded. With the growth in ship sizes and the introduction of new building methods it has been recognized that a revised shipyard layout will be advantageous. Advantages to be gained, apart from the ability to construct larger vessels, are primarily, a uniform work load, a shorter ship build cycle, and economies in construction practices. These are...

Transverse Stresses

When a ship experiences transverse forces these tend to change the shape of the vessel's cross sections and thereby introduce transverse stresses. These forces may be produced by hydrostatic loads and impact of seas or cargo and structural weights both directly and as the result of reactions due to change of ship motion. racking When a ship is rolling, the deck tends to move laterally relative to the bottom structure, and the shell on one side to move vertically relative to the other side. This...

Cargo Pumping and Piping Arrangements in Tankers

Cargo Arrangement And Construction

Cargo pumps are provided in tankers to load and discharge cargo, and also to ballast some of the tanks which becomes necessary when making voyages in the unloaded condition. Many modern tankers have clean ballast capacity and these tanks are served by a separate pumping system. The particular cargo pumping system adopted depends very much on the range of cargo carried. A fairly straightforward system is available for the larger bulk oil carrier, carrying a single product. Where smaller tankers...

Masts and Sampson Posts

Masts on a general cargo ship may fulfil a number of functions but their prime use in modern ships is to carry and support the derricks used for cargo handling. Single masts are often fitted, but many ships now have various forms of bipod mast which are often more suitable for supporting derricks, although some types can restrict the view from the bridge. Sampson posts are also popular, particularly at the ends of houses, and are often fitted at the other hatches also. The strength of masts and...

General Arrangement of Gas Carriers

Gas carriers have a similar overall arrangement to tankers in that their machinery and accommodation are aft and the cargo containment is spread over the rest of the ship to forward where the forecastle is fitted. Specific gravity of LPG cargoes can vary from 0.58 to 0.97 whilst LNG ships are often designed for a cargo specific gravity of 0.5 so that a characteristic of LNG ships in particular and most LPG ships is their low draft and high freeboards. Water ballast cannot be carried in the...

After End Structure

The machinery is arranged aft in ocean-going tankers, and a transversely framed double bottom structure is adopted in way of the machinery space. Constructional details of this double bottom are similar to those of the conventional dry cargo ship with floors at each frame space, additional side girders, and the engine seating integral with the bottom stiffening members. Transverse or longitudinal side and deck framing may be adopted in way of the engine room and aft of this space. If...

Lloyds Register Classification Symbols

All ships classed by Lloyd's Register of Shipping are assigned one or more character symbols. The majority of ships are assigned the characters 100A1 or 100A1. The character figure 100 is assigned to all ships considered suitable for sea-going service. The character letter A is assigned to all ships which are built in accordance with or accepted into class as complying with the Society's Rules and Regulations. The character figure 1 is assigned to ships carrying on board anchor and or mooring...

Ship Dimensions and Form

Keel Freeboard Deck Beam The Side

The hull form of a ship may be defined by a number of dimensions and terms which are often referred to during and after building the vessel. An explanation of the principal terms is given below After Perpendicular AP A perpendicular drawn to the waterline at the point where the aft side of the rudder post meets the summer load line. Where no rudder post is fitted it is taken as the centre line of the rudder stock. Forward Perpendicular FP A perpendicular drawn to the waterline at the point...

Preparation of the Design

Design Spiral Ship Construction

The initial design of a ship generally proceeds through three stages concept preliminary and contract design. The process of initial design is often illustrated by the design spiral Figure 1.1 which indicates that given the objectives of the design, the designer works towards the best solution adjusting and balancing the interrelated parameters as he goes. A concept design should, from the objectives, provide sufficient information for a basic techno-economic assessment of the alternatives to...

Dry Cargo Ships

If the development of the dry cargo ship from the time of introduction of steam propulsion is considered the pattern of change is similar to that shown in Figure 3.2. The first steam ships followed in most respects the design of the sailing ship having a flush deck with the machinery openings protected only by low coamings and glass skylights. At quite an early stage it was decided to protect the machinery openings with an enclosed bridge structure. Erections forming a forecastle and poop were...

Information Provided By Designer In Ship Construction

Formerly Lecturer in Naval Architecture Department of Maritime Studies Plymouth Polytechnic now University of Plymouth Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier pic group D. J. Eyres 1972, 1978, 1988, 1994, 2001 All rights reserved. No part of this publication may be reproduced in any material form including photocopying or storing in any medium by electronic...