5.2 THE CRUDE OIL WASHING PROGRAMME
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.