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The primary purpose of crude oil washing (COW), is to minimise the amount of residue (ROB), in the ship's cargo tanks at the completion of discharge. To put it positively, the intention of a good COW programme is to maximize the cargo outturn from the ship.
The program cannot be prepared until the cargo discharge plan has been completed. The best method of preparing the COW plan is to use a diagram such as figure 5.2.1.
To prepare this plan, the chief officer must know the washing patterns of the COW guns fitted on his ship and the times required for each cycle of their washing programme.
His objective will be to prepare a plan which begins COW operations as soon as the cargo tanks have been sufficiently discharged. This will minimise the delay before residues and clingage are attacked by the COW stream. His evaluation of the comparative discharge rates and washing times will also indicate when COW must be suspended at the end of a cycle to permit draining of a cargo tank before the tank bottom COW cycle is started.
Because of the work load in the discharge port, it may be necessary for the chief officer to delegate the responsibility for the execution of the COW programme to an assistant. This assistant must be both familiar with the vessel's COW systems and possessor of a valid COW certificate of competency. See section 5.27 for detailed COW operations procedures.

5.2.1 Charterer's instructions
Charterer's instructions take precedence over all other instructions in setting the COW programme, provided safe practice as set out in the vessel's Crude oil washing and equipment manual is observed. Charterers should advise the master, in the cargo orders, of the degree of crude oil washing required and which grades of crude are to be used/washed. If owner or receiver wishes to modify or expand those instructions, their recommendations must be accepted by the charterer before being included in the COW programme.

A detailed discharge plan bar chart with COW.

5.2.2 COW for shipyard
If the ship is scheduled for shipyard following the discharge port, then a COW programme which includes all cargo and slop tanks is in the owner's interest. This may require some negotiation with the charterer regarding the allocation of time in berth.

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