Cleaning. When an oil tanker or chemical tanker carries one cargo, it must usually be cleaned before the next cargo and also to reduce the "clingage" and residues on the parts of the ship's structure inside the cargo spaces.
Cleaning is also necessary for pollution prevention so that, if necessary, ballast that has to be taken into cargo tanks is not "dirty ballast". Tank cleaning is a complex activity and requires special training and supervision. In crude oil tankers, washing with crude oil during the discharge cycle is also carried out to reduce the sediment within the tanks and to attempt to ensure that tanks are cleaned for ballast. (This is referred to as "Crude Oil Washing" or abbreviated to "COW".)
In a charterparty for oil tankers, a clause usually provides for expenses and responsibilities for tank cleaning. For example, in the TANIKERVOY 87 tanker voyage charterparty, it is stated:
"(a) The master shall exercise due diligence to keep the tanks, pipes and pumps of the vessel suitable for the cargo . . .
(b) Charterers may place a representative on board the vessel at any loading and/or discharging port and Owners shall co-operate to facilitate his inspection of the vessel and observation of cargo transfer operations.
(c) Charterers may require inspection of the vessel's tanks at loading and discharging ports to ascertain the quantity and quality of the cargo, water and residues on board . . . . Any delay to the vessel caused by such inspection and measurement and sampling . . . shall count as laytime or for demurrage if the vessel is on demurrage."
This clause also contains a provision for de-pressurising the tanks if the vessel is using an "Inert gas system". (as is required with crude oil washing). If an inspector wishes to sight the bottom of the tank, the tank will have to be depressurised and de-inerted and their re-inerted for loading. This is expensive in time and in fuel costs. The charterparty should specify the responsibility for payment. The shipowner should realise that potential liabilities can result from the vessel's failure to clean tanks to the satisfaction of the inspector and also for the delay that may occur.
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