Start with the cargo and the approved procedure
On a chemical tanker, “wash the tank” is not a complete instruction. Under MARPOL Annex II, discharge controls for noxious liquid substances depend on the substance and applicable conditions. Some residues must go to reception facilities until the relevant discharge criteria are met; the requirements vary by substance category. That makes the cargo identity and its applicable instructions the starting point—not a generic wash routine. [2]
Before planning a prewash, check the cargo-specific requirements and the ship’s approved Procedures and Arrangements Manual. The Annex describes different procedures for different residue types. For example, its prewash guidance addresses rotary water jets, maintaining flow toward the suction point, and continuously pumping out slops to keep the liquid remaining in the tank to a minimum. It also describes additional washing and thorough stripping where that condition cannot be achieved. Those details are not a substitute for the approved procedure for the tank and cargo. [0][1]
Annex II of MARPOL: Regulations for the Control of Pollution by Noxious Liquid Substances in Bulk · MEPC.118(52): Revised MARPOL Annex II · International Convention for the Prevention of Pollution from Ships (MARPOL)
Make the residue route workable before washing
A cleaning plan also needs a destination. Where the applicable procedure requires prewash residue to be discharged ashore, confirm the planned reception-facility handover before starting. The IMO’s Annex II text specifies discharge of prewash washings to a reception facility in the relevant cases, and its prewash guidance says shore discharge continues until the tank is empty. [0][1]
Translate that requirement into an operational sequence: identify the tanks and lines involved, establish how the washings will reach the reception facility, and coordinate the expected transfer with the shore side. Treat the tank, pump, piping and shore-reception route as one connected operation. If any part of the intended route is unavailable or differs from the plan, pause to resolve the arrangement rather than assuming the washings can be redirected or discharged elsewhere. This is a practical planning recommendation based on the required shore-discharge route, not a claim that one sequence fits every ship or cargo. [0][1][3]
Annex II of MARPOL: Regulations for the Control of Pollution by Noxious Liquid Substances in Bulk · MEPC.118(52): Revised MARPOL Annex II · Reception facilities
Control the wash, not just the wash-water supply
During a required prewash, the procedure calls for more than operating a tank-cleaning machine. Annex II guidance describes keeping the amount of liquid in the tank low by pumping out slops and promoting flow toward the suction point. Where the specified condition cannot be met, the guidance calls for repeated washing cycles with thorough stripping between them. The applicable procedure also addresses washing-machine operation and, after washing, continued operation long enough to flush the pipeline, pump and filter. [1]
For the person supervising, the useful checkpoints are therefore operational: Is the intended suction path working? Are slops being removed as planned? Has the required washing coverage and sequence been completed? Have the connected pump and lines been flushed as directed? Record what was actually done and raise deviations promptly. These checks help connect the written procedure to observable steps, without replacing the ship-specific method or the cargo’s requirements. [0][1]
Annex II of MARPOL: Regulations for the Control of Pollution by Noxious Liquid Substances in Bulk · MEPC.118(52): Revised MARPOL Annex II
Close out the handover and the record
Do not treat the job as complete when the washing machine stops. Where the applicable procedure requires it, continue the shore discharge until the tank is empty and confirm that the residue has reached the designated reception facility. The Annex also provides for the Cargo Record Book to document relevant operations; its text addresses entries for prewash and related control, including surveyor endorsement where required. [0]
A useful closeout brings the physical and documentary sides together: match the tanks washed with the shore-reception handover, confirm that the required tank and connected-system steps are complete, and ensure the operation is recorded under the applicable procedure. Reception facilities are a crucial part of MARPOL implementation, the IMO notes, so confirming the receiving arrangement is not merely an administrative afterthought. [0][3]
The central discipline is simple: identify the applicable cargo-specific rule, follow the approved wash procedure, maintain the planned residue route, and close the record against the work actually completed. That makes prewash a controlled handover—from tank to shore—rather than an isolated cleaning task. [0][1][3]
Annex II of MARPOL: Regulations for the Control of Pollution by Noxious Liquid Substances in Bulk · MEPC.118(52): Revised MARPOL Annex II · Reception facilities