Crude Oil Washing
Abbreviation: COW
Cleaning crude oil tanks with their own cargo as the wash medium, replacing earlier seawater-flush methods.
In practice
Conducted during discharge by the cargo officer with the master and shore terminal informed. The fixed COW machines are programmed and tank atmosphere kept inert; oxygen content monitored continuously. Skipping or short-cutting COW under time pressure is a common SIRE 2.0 finding.
Regulatory detail & full definition
Mandatory for crude tankers > 20,000 DWT under MARPOL Annex I Reg. 33. Tanks are washed during discharge using high-pressure crude oil through fixed machines. Reduces clingage and slop generation, and lowers oil pollution risk vs the older Load-On-Top method. Inert gas (< 8% O2) must be present throughout.
Authoritative source: MARPOL Annex I (Oil) ↗
Related
Source: MARPOL Annex I Reg. 33; IMO Resolution A.446(XI)
High confidence
Editorial confidence: how we grade.