Answer Construction Question 8

Question 8: Describe the arrangement of tank top and double bottom in the machinery space making particular reference to the structure and scantlings below the main engine. Show the method adopted in the arrangement of D.B. tanks to avoid contamination of fresh water, fuel oil and lube oil stored in D.B. tanks.

Answer:The construction of the double bottom under the machinery space regardless of framing system has solid plate floors at every frame space under the main engine. Besides the continuous centre girder of greater thickness, additional side girders are fitted outboard of the main engine seating.

The double bottom height is usually increased to allow for the alignment of the shafting system, as well as to provide fuel oil, diesel oil, lubricating oil and Fresh Water tank of suitable capacities. Where the double bottom is increased in depth above the normal, continuity of strength is maintained by the gradual sloping of the tank top and inter-costals girders between the machinery space and the adjacent compartments.

Heavy plate (40 mm) support with bar stiffener is provided on the tank top for the seating of main engine bedplate and thrust block, which are bolted direct to heavy plate, incorporated in the tank top, the bolts penetrating into cofferdams.

The lubricating oil drain tank, fuel oil tanks, diesel oil tank, fresh water tanks in the double bottom space are separated by cofferdams to avoid contamination. Access to these double bottom tanks and cofferdams is provided by water-tight manhole doors. Docking plugs are fitted in all double bottom tanks for complete draining in dry dock for inspection purpose. Air pipes and sounding pipes are also fitted to these double bottom tanks and the tanks are tested by the maximum service pressure head.