PRACTICAL SHIPBUILDING Design.—In order that a naval architect may be in a position to prepare a design for a new ship he must first be informed as fully as possible of the requirements which he is to meet. These include the trade or service on which the ship will be engaged; the impor tant features that it is desired to embody (e.g., in a warship the armament and protection to be carried) ; the speed and endurance to be aimed at, and any limitations in dimensions or cost. In the case of a British warship design the requirements are laid down in the first place by the naval staff. The Director of Naval Con struction then prepares outline or sketch designs complying as nearly as possible with these requirements; and after full discus sion one of these designs is selected and approved. This design is then worked out in detail, and complete drawings and specifications prepared.
The problems of naval design differ in many respects from those occurring in connection with merchant ships (q.v.). Usually the most important consideration is that of weight ; for it is necessary to obtain the greatest possible offensive power, defensive qualities and speed in as light and small a ship as practicable. This has led to many interesting developments in structural design ; ma terials of high elastic strength are employed wherever possible, and scantlings are cut to the greatest possible extent consistent with safety. Many fittings and fixtures, and even minor portions of the hull, are made of aluminium alloy or other light materials; and great progress has been made in designing the arrangement of structure so that the material is disposed, as far as practicable, where it is most effective in contributing to the strength of the ship. The importance of this can be realized when it is remem bered that in a high-speed ship every ton saved enables the ship as a whole to be lightened by about three tons. The designer's experience is also called upon to dispose the armament so as to be as effective as possible in all directions, and avoid mutual inter ference by gun blast, to ensure that such protection as is carried shall shield the vitals of the ship for a minimum expenditure of weight, and to arrange the main and auxiliary machinery so that it encroaches as little as possible on other portions of the ship, particularly those devoted to the accommodation of the personnel and the stowage of ammunition. The form of the ship is largely
determined by consideration of the minimum resistance at high speed ; in addition adequate stability has to be provided under all conditions (including the cases when the ship has been damaged by gunfire or after attack by mine or torpedo) and the trim and seaworthiness of the ship rendered satisfactory.
The information prepared by the naval architect and supplied to the shipbuilders consists usually of a sheer drawing showing the form of the ship, a profile, various sections and a plan of each deck showing the general arrangement, and the structural sections. With these is a complete specification laying down the materials to be used and their scantlings, and containing a description of all internal arrangements, the fixtures, fittings and stores to be sup plied, and the trials to be finally carried out.
The method adopted for designing a ship cannot be described here at length. It may be observed, however, that the process is tentative, approximate dimensions, form and horse-power being first assumed and the design worked out sufficiently to ascertain whether it meets the requirements. If it fails to do so, or if any defects are revealed, the dimensions, etc., are altered and the process repeated until a design is obtained which satisfies the conditions imposed. The success of the final design depends on the skill and experience of the naval architect, who has to base his plans on his knowledge of existing ships, whilst introducing such improvements as he is able, having regard to progress in materials and machinery and more accurate knowledge of the conditions of service.