Load on Top
Abbreviation: LOT
Pre-COW practice of letting tank washings settle, decanting the water, and loading new cargo on top of the oil residue.
In practice
Largely retired in modern fleets. Where still used, the cargo officer documents tank washings, settling time, and ODME readings in the Oil Record Book Part II. Improper LOT followed by overboard discharge is the classic source of MARPOL Annex I prosecutions.
Regulatory detail & full definition
Load-on-top is a pre-Crude-Oil-Washing method of handling oil-tanker tank washings: after discharge the dirty ballast and washings are left to settle in a slop tank, the separated water underneath is decanted overboard within the MARPOL limits, and the retained oil residue (the slops) is kept on board so that the next cargo is loaded on top of it. It has been largely superseded by Crude Oil Washing under MARPOL Annex I but is still permitted for some product tankers and in certain circumstances. Discharge of the separated water is governed by the 1/15,000 rule and monitored by Oil Discharge Monitoring Equipment (ODME).
Authoritative source: MARPOL Annex I (Oil) ↗
Related
Source: MARPOL Annex I Reg. 34 (control of discharge of oil)
High confidence
Editorial confidence: how we grade.