Tank top

The tank top is the inner-bottom plating that forms the floor of a cargo hold and the top boundary of the double-bottom tanks beneath it. It seals the double bottom (which holds fuel, fresh water, or ballast) from the cargo space, carries the cargo and any tween-deck loads down into the floors and girders of the double-bottom structure, and takes wear from grabs during bulk discharge, so it is plated heavier in the holds. Its strength is set by the tank-top design load, the static cargo or ballast head plus dynamic factors, under the class double-bottom rules. In a bulk carrier the hopper plating slopes up from the tank top to the side, forming the self-trimming hold.