including the design of the ship’s pipeline system. Once it has been established that the cargo is flowing correctly, the discharge rate should be increased to the agreed maximum. The rate may be
restricted either by back pressure or by the capacity of the ship’s pumps. The rate of discharge should be carefully monitored throughout and recorded at intervals of no more than one hour. These records should show not only the amount of cargo discharged by volume but also the shore back pressure, the pressure at the ship’s manifold, the speed of the cargo pumps and steam pressure or, in the case of electrical pumps, the amperage. If COW is being carried out, this operation must be closely monitored. Careful recording of the discharge in the ship’s logs is essential if claims are to be successfully defended.
The effective stripping of the tanks is important since claims will undoubtedly be made against the owner for quantities of cargo remaining onboard. Provided the ship has a good stern trim, the tanks have been well cleaned and prepared prior to loading and provided also that the ship’s pumps and pipelines are in sound condition, it should be possible to ensure that a negligible quantity is left onboard. In the case of light or clean products there should be no problem although where heavier or heated cargoes are concerned, there will inevitably be some clingage and perhaps some sediment remaining. COW will help to reduce these quantities and care should be exercised when stripping heated cargoes to ensure that the tanks are drained quickly, since once the level of the cargo falls below the heating coils, heat will be lost quickly and difficulties may be encountered.
Whatever type of oil is carried, it will be necessary to be able to demonstrate that ship’s valves, lines and pumps were in good condition at the time of discharge, because this has an impact on the question of ‘pumpability’. It might be assumed that oil is pumpable or unpumpable in the sense that it is liquid or not liquid. From the point of view of cargo claims however, it must also be considered whether, even if the cargo was liquid, it could be pumped by the vessel’s equipment. It is possible that small quantities of oil, particularly where high gas cargoes are concerned, cannot be picked up by the pumps without the pumps gassing up. It could be that due to sediments from the cargo or shore restrictions on trim, the oil is liquid but cannot run to the suction. The master should call in a local UK Club surveyor if he experiences difficulty in obtaining a suitable dry tank certificate. If pressure is applied to the ship to sail before the surveyor can attend, the master should protest to the receivers and to the receivers’ surveyor. If the surveyors are not prepared to certify cargo remaining onboard as unpumpable, they should
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be invited to inspect the ship’s pumps. The receivers should be informed that if they consider the cargo to be pumpable, the ship is prepared to continue to attempt to pump it until the UK Club surveyor arrives. Owners should ensure that the maintenance records for the cargo pumps are carefully preserved and that they are available when such disputes arise. Surveyors who certify cargo as pumpable should be required to prove that they have tested the nature of the cargo and have ascertained that it can and does reach the suction in the cargo tank.
ROB claims may therefore arise in three different ways:
● By loss of heating or inadequate heating onboard ships, sometimes coupled with low ambient temperatures at the time of discharge.
● The physical properties of the oil and the ability of the pumps to pump it. The possibility of pumps gassing up and loss of suction must be taken into consideration.
● Cargo sediments or trim restrictions which prevent the free flow of oil to the tank suction.
In the case of crude which does not require heating or which has a high vapour pressure, good crude oil washing and a good stern trim will overcome most problems.
Frequently the charterparty will call for COW ‘in accordance with Marpol’ and will allow additional time for discharge when COW is performed. Naturally, if the receiving installation will not allow satisfactory stern trim or if they refuse COW either in whole or in part then the master should protest to the terminal and to the charterers, stating that the vessel cannot be held responsible for any resulting cargo losses.
On completion of discharge
When the cargo has been completely discharged with all tanks and pipelines well drained, the cargo system should be shut down and all tank valves closed. A final tank inspection is then carried out and inevitably particular attention will be paid by the shore representatives to any cargo remaining onboard. All void spaces, including ballast tanks and cofferdams should be checked to ensure that no leakage of cargo has occurred. This is particularly relevant on OBO vessels.
Dry tank certificate
After discharge, a dry tank certificate will ideally be issued, signed by an appropriate shore representative describing any remaining cargo as ‘unpumpable’ and
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