3.26 BALANCE CARGO TANKS

Cargo loading is normally completed in one or two cargo tanks, selected according to the draft and trim restrictions and depending on the cargo layout. In the ideal case, loading can be finished into a single centre tank near amidship, one with zero, or nearly zero trimming effect. As it is loaded the ship is immersed 'bodily' or equally fore and aft. Where the ship will be loaded to its marks, it is desirable to leave one or more tanks near amidship slack to reduce the sagging stress on the hull. So, selection of an amidship tank for the trimming tank achieves both ends.
When the last trimming tank will be slack at the end of the loading operation, there is little concern for an overflow while finishing the loading. The shore is given the usual notice for stopping the flow of cargo and the stop order is given when the balance cargo tank is one or two centimetres from the desired ullage.
When loading a cubic cargo, such as gasoline or light crudes, all tanks are filled to the minimum safe ullage, including the last tank. In this case, the preparations indicated in section 3.23 should be observed. If the shore terminal does not stop the flow of cargo in the time expected, the ship will have no space on board to divert the additional cargo to and will be forced to close the manifold valve against the shore pressure to prevent an overflow. The best way to prevent this from happening is to set the stop gauge for the balance cargo tank at a lower level than the other tanks and to have a backup stop signal ready at hand in the event that the radio order to stop loading is not properly received or executed.