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UNIT 6. Building Systems and Their Characteristics

Introduction. Every ship hull is a kind of a box like carrier which when in service, whether it is floating or sailing, is subjected to the different kinds of' static and dynamic forces which act transversely, longitudinally and torsionally upon the ship hull. Therefore the ship hull must be designed and built in such a way that it can withstand all the stresses caused by these forces. Which of these forces will be predominant depends on the size and type of a ship, the cargo it carries, the distribution of weight, the seaway conditions etc.

A ship hull consists of the transverse members which provide the transverse strength of the ship, and of the longitudinal members which ensure the longitudinal strength of the ship. Besides these there are other building members that provide the watertightness of the ship and finally different kinds of fittings and equipment that are required to be fitted on a ship. The transverse and longitudinal members of the ship must be arranged and disposed in such a way that they will ensure the torsional strength of the ship hull as well.

Every ship hull must be provided with the basic structural members which are the bearers of the transverse strength (ordinary frames, web frames or side transverses; ordinary beams, web beams or deck transverses; floors or bottom transverses) and also with the basic structural members which are the bearers of the longitudinal strength (the keel plate, the centre girder, side girders, the sheer strake, the deck stringer plate, and that portion of the plating that is at the farthest distance from the neutral axis). Some parts of the ship hull, however, may be built transversely or longitudinally depending upon the size and type of the ship and the rules of the classification societies to which a ship is built. This primarily refers to the stiffening system of the side, deck and bottom plating, which together form the outside plating of the ship hull. The stiffening of the hull plating is closely related to the stiffening of the transverse and longitudinal bulkheads, the different kinds of tanks, and also to the inner bottom plating if the ship is provided with a double bottom.

1. The transverse system of building. The side plating is stiffened by the transverse frames, the deck plating by the beams, and the bottom plating by the floors (plate floors or watertight floors).

2. The longitudinal system of building. The side plating is stiffened by the side longitudinals, the deck plating by the deck longitudinals, and the bottom plating by the bottom longitudinals.

3. The combination system of building. The side plating is stiffened by the transverse frames, the deck plating by the deck longitudinals, and the bottom plating by the bottom longitudinals.

FIG. 1 A TABLE SHOWING THE CHARACTERISTIC FEATURES OF THE BUILDING SYSTEM

This classification table of the three building systems primarily refers to that part of the ship hull which extends between the fore and after peak, i.e. it refers to the parallel middle body of very large ships.

The peaks are generally built in a special transverse system of building regardless of the system that is used for the remaining part of the hull. This system has proved to be most convenient for that part of the hull where its form is abruptly changed, its breadth is suddenly reduced, and where a number of auxiliary units and equipment must be placed and fitted.