Volume enclosed between the ship's bottom up to the turn of
the bilge, abaft the collision bulkhead and forward of the aft bulkhead and tank
top in the cargo holds is termed as double bottom tanks. Double bottom tanks
are identified numerically from forward to aft.
Double bottom tanks do not extend in way of the peak tanks
and Main Engine room space.
Double bottom tanks are sub-divided longitudinally to form
Port and Starboard Tank by water tight girders or walls of the duct keel, Double
bottom tanks are divided by water tight floors.
Double bottom tanks are strengthened by bracket floors,
solid floors, tank side brackets, inter coastal girders, center girder,
longitudinal members which are located under the tank top and on the inner surface
of the bottom plating, all these members jointly contribute in strengthening
longitudinal and transversely the bottom structure of the ship.
Tank side brackets are fitted along the length of the double
bottom tanks in way of the turn of the bilge.
Double bottom tanks are generally used for ballast water,
fuel, fresh water / boiler feed water.
Every double bottom tank must be provided with air pipes,
sounding pipes, filling and suction pipe line arrangements.
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