Exam Question

The construction of the double bottom in the machinery space regardless of the framing system has solid plate floors at every frame space under the main engine. Additional side girders are fitted outboard of the main engine seating, as required. The double-bottom height is usually increased to provide fuel oil, lubricating oil and fresh water tanks of suitable capacities. Shaft alignment also requires an increase in the double-bottom height or a raised seating, the former method usually being adopted.
Continuity of strength is ensured and maintained by gradually sloping the tank top height and internal structure to the required position. Additional support and stiffening is necessary for the main engines, boilers, etc., to provide a vibration-resistant solid platform capable of supporting the concentrated loads. On slow- speed diesel-engined ships, the tank top plating is increased to 40 mm thickness or thereabouts in way of the engine bedplate. This is achieved by using a special insert plate which is the length of the engine including the thrust block in size. Additional heavy girders are also fitted under this plate and in other positions under heavy machinery as required. Plating and girder material in the machinery spaces is of increased scantlings in the order of 10 per cent.
The method adopted.
A cellular void space within a ships structure is called a coffer dam. Like a bulkhead separates two spaces or divides a space into two, a coffer dam does the same with a larger degree of integrity since it incorporates a void which would contain any breach of either of the boundaries. This would contain the leakage and prevent it spreading into other areas. A cofferdam can be defined as an empty space separating compartments to prevent the contents of one compartment from entering another in case of leakage.