Ship Construction

George J. Bruce,Keith W. Hutchinson

• Editore: Butterworth-Heinemann
• Anno: 2012
• ISBN:
  9780080972404
• Edizione: 7
• Argomento: Tecnología e ingeniería
• Categoria: Ciencia y tecnología militares

Ship Construction, Seventh Edition, offers guidance for ship design and shipbuilding from start to finish. It provides an overview of current shipyard techniques, safety in shipyard practice, materials and strengths, welding and cutting, and ship structure, along with computer-aided design and manufacture, international regulations for ship types, new materials, and fabrication technologies. Comprised of seven sections divided into 32 chapters, the book introduces the reader to shipbuilding, including the basic design of a ship, ship dimensions and category, and development of ship types. It then turns to a discussion of rules and regulations governing ship strength and structural integrity, testing of materials used in ship construction, and welding practices and weld testing. Developments in the layout of a shipyard are also considered, along with development of the initial structural and arrangement design into information usable by production; the processes involved in the preparation and machining of a plate or section; and how a ship structure is assembled. A number of websites containing further information, drawings, and photographs, as well as regulations that apply to ships and their construction, are listed at the end of most chapters. This text is an invaluable resource for students of marine sciences and technology, practicing marine engineers and naval architects, and professionals from other disciplines ranging from law to insurance, accounting, and logistics.

• Covers the complete ship construction process including the development of ship types, materials and strengths, welding and cutting and ship structure, with numerous clear line diagrams included for ease of understanding
• Includes the latest developments in technology and shipyard methods, including a new chapter on computer-aided design and manufacture
• Essential for students and professionals, particularly those working in shipyards, supervising ship construction, conversion and maintenance

Part 1

Introduction to Shipbuilding

1

Basic design of the ship

Chapter Outline

Preparation of the design

Information provided by design

Purchase of a new vessel

Ship contracts

Further reading

Some useful websites

The key requirement of a new ship is that it can trade profitably, so economics is of prime importance in designing a merchant ship. An owner requires a ship that will give the best possible returns for the owner’s initial investment and running costs. The final design should be arrived at taking into account not only present economic considerations, but also those likely to develop within the life of the ship. This is especially the case for some trades, for example LNG, where the ship is expected to work the same route for its working life. Design for operation is the result. For other ships, including bulk carriers, the first cost of the ship is the major factor for the owner and the ship may be designed for ease of production. Resale value is also often a major consideration, leading to design for maintenance.

With the aid of computers it is possible to make a study of a large number of varying design parameters and to arrive at a ship design that is not only technically feasible but, more importantly, is the most economically efficient. Ideally the design will take into consideration first cost, operating cost, and future maintenance.

Preparation of the design

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 the designer goes.

Figure 1.1 Design spiral.

A concept design should, from the objectives, provide sufficient information for a basic techno-economic assessment of the alternatives to be made. Economic criteria that may be derived for commercial ship designs and used to measure their profitability are net present value, discounted cash flow, or required freight rate. Preliminary design refines and analyzes the agreed concept design, fills out the arrangements and structure, and aims to optimize service performance. At this stage the builder should have sufficient information to tender. Contract design details the final arrangements and systems agreed with the owner and satisfies the building contract conditions.

The design of the ship is not complete at this stage, rather for the major effort in resources it has only just started. Post-contract design requires confirmation that the ship will meet all operational requirements, including safety requirements from regulators. It also entails in particular design for production where the structure, outfit, and systems are planned in detail to achieve a cost- and time-effective building cycle. Production of the ship must also be given consideration in the earlier design stages, particularly where it places constraints on the design or can affect costs. The post-contract design will also ideally consider the future maintainability of the ship in the arrangement of equipment and services.

Information provided by design

When the preliminary design has been selected the following information is available:

• Dimensions

• Displacement

• Stability

• Propulsive characteristics and hull form

• Preliminary general arrangement

• Principal structural details.

Each item of information may be considered in more detail, together with any restraints placed on these items by the ship’s service or other factors outside the designer’s control.

1. The dimensions of most ships are primarily influenced by the cargo-carrying capacity of the vessel. In the case of the passenger vessel, dimensions are influenced by the height and length of superstructure containing the accommodation. Length, where not specified as a maximum, should be a minimum consistent with the required speed and hull form. Increase of length produces higher longitudinal bending stresses requiring additional strengthening and a greater displacement for the same cargo weight. Breadth may be such as to provide adequate transverse stability. A minimum depth is controlled by the draft plus statutory freeboard, but an increase in depth will result in a reduction of the longitudinal bending stresses, providing an increase in strength, or allowing a reduction in scantlings (i.e. plate thickness/size of stiffening members etc.). Increased depth is therefore preferred to increased length. Draft is often limited by area of operation, but if it can be increased to give a greater depth this can be an advantage.
Many vessels are required to make passages through various canals and straits and pass under bridges within enclosed waters, and this will place a limitation on their dimensions. For example, locks in the Panama Canal and St Lawrence Seaway limit length, breadth, and draft. At the time of writing, the Malacca Straits main shipping channel is about 25 meters deep and the Suez Canal could accommodate ships with a beam of up to 75 meters and maximum draft of 16 metres. A maximum air draft on container ships of around 40 meters is very close to clear the heights of the Gerard Desmond Bridge, Long Beach, California and Bayonne Bridge, New York. Newer bridges over the Suez Canal at 65 meters and over the Bosporus at 62 meters provide greater clearance.

2. Displacement is made up of lightweight plus deadweight. The lightweight is the weight of vessel as built and ready for sea. Deadweight is the difference between the lightweight and loaded displacement, i.e. it is the weight of cargo plus weights of fuel, stores, water ballast, fresh water, crew and passengers, and baggage. When carrying high-density cargoes (e.g. ore) it is desirable to keep the lightweight as small as possible, consistent with adequate strength. Since only cargo weight of the total deadweight is earning capital, other items should be kept to a minimum as long as the vessel fulfills its commitments.

3. In determining the dimensions, statical stability is kept in mind in order to ensure that this is sufficient in all possible conditions of loading. Beam and depth are the main influences. Statutory freeboard and sheer are important together with the weight distribution in arranging the vessel’s layout.

4. Adequate propulsive performance will ensure that the vessel attains the required speeds. The hull form is such that economically it offers a minimum resistance to motion so that a minimum power with economically lightest machinery is installed without losing the specified cargo capacity.
A service speed is the average speed at sea with normal service power and loading under average weather conditions. A trial speed is the average speed obtained using the maximum power over a measured course in calm weather with a clean hull and specified load condition. This speed may be a knot or so more than the service speed.
Unless a hull form similar to that of a known performance vessel is used, a computer-generated hull form and its predicted propulsive performance can be determined. The propulsive performance can be confirmed by subsequent tank testing of a model hull, which may suggest further beneficial modifications.
The owner may specify the type and make of main propulsion machinery installation with which their operating personnel are familiar.

5. The general arrangement is prepared in cooperation with the owner, allowing for standards of accommodation particular to that company, also specific cargo and stowage requirements. Efficient working of the vessel must be kept in mind throughout and compliance with the regulations of the various authorities involved on trade routes must also be taken into account. Some consultation with shipboard employees’ representative organizations may also be necessary in the final accommodation arrangements.

6. Almost all vessels will be built to the requirements of a classification society such as Lloyd’s Register. The standard of classification specified will determine the structural scantlings and these will be taken out by the shipbuilder. The determination of the minimum hull structural scantlings can be carried out by means of computer programs made available to the shipyard by the classification society. Owners may specify thicknesses and material requirements in excess of those required by the classification societies and special structural features peculiar to the trade or owner’s fleet may be asked for.

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 labor factors, and cas...