Capt. Abhishek Mishra


COW is a system whereby oil tanks on a tanker are cleaned out between voyages not with water, but with crude oil – the cargo itself. The solvent action of the crude oil makes the cleaning process far more effective than when water is used.


Manual is on board to give information on ship-specific cow system and operational guidelines for effective COW.

COW is mandatory on new tankers under the International Convention for the Prevention of Pollution by Ships (MARPOL).

Advantages of Crude Oil Washing:

  •  Increase Cargo outturn
  •  Reduce Sludge Accumulation
  •  Reduce Gas freeing time
  •  Reduce manual cleaning

Disadvantages of Crude oil Washing:

  • Does not Eliminate water washing
  • Need for additional equipment
  • Specialized man power required
  • Increased stay at discharge port
  • Increased workload
  • Increased corrosion in the tank.

Parts of COW System:

  • Pumps ( Dedicated pumps or Cargo Pumps )
  • Piping (Fixed Piping independent of Fire Line & other piping system)
  • Fixed Machines ( Programmable / Non-Programmable)
  • Stripping System : ( Cargo educators / Stripping Pumps and existing piping)Precautions during COW operations:

There are prescribed checklists to be followed for carrying out Crude Oil Washing Operations:

1. Before arrival at Port:

 COW Plan has to be ready together with discharge operations.
 Permission has to be obtained from the terminal for carrying out COW
 Confirm that particular oil is suitable for the COW operations.
 Oxygen analyzing equipment is calibrated, tested and ready for use.
 IG system is tested and fully operational.
 All the Inert gas valves of tanks confirmed opened & locked.
 Tank Cleaning Line/pumps etc pressure tested for leakage etc.
 All Gauges are working satisfactory.
 Cargo Watch schedule with respect to COW operations ready.
 All the valves of Tank Cleaning system confirmed shut.
 Cargo Tank high high level alarms has been tested.

2. After arrival at Port & During operations :

 COW Plan discussed with Ship Staff before operations.
 Check all cargo tanks have positive pressure.
 Oxygen Content of tanks is below 8% by Vol.
 Check Communication system is in good order.
 Water level in the deck seal is sufficient.
 Terminal & Ship staff informed when starting operations.

 Level of collecting tank normal and being monitored.
 Oxygen content of IG delivered in tanks is below 5%.
 Check only designated cargo tanks are being washed and no other tank
machine is working.
 Tanks are maintained with positive IG Pressure.
 Stripping is being done effectively.
 Enough time is given to tank before checking sounding. This is to allow time for
dissipation of static electricity developed in tank during washing.
3. After COW Operations :
 All Tank washing lines are properly drained.
 All Tank Cleaning valves are shut.
 Terminal informed & ship staff informed after completion of tank washing operations and log prepared.

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