A dedicated tank on tankers used to collect cargo residues and tank washing water, allowing oil-water separation before discharge.
Quick facts
Regulation
MARPOL Annex I
In practice
Slop management requires careful stratification time before the water underrun is discharged. Officers record every slop tank transfer and overboard discharge in the Oil Record Book Part I. At the end of the voyage the remaining oil-rich slop is either retained as a base for the next cargo on crude tankers, discharged to a port reception facility, or pumped to a shore terminal. Port state control officers pay particular attention to the slop tank records to detect patterns of illegal discharge, and discrepancies between oil received, cargo outturn figures, and slop volumes often trigger detailed investigation.
Regulatory detail & full definition
The slop tank is a dedicated tank — usually one or two of the ship's cargo tank compartments designated for this purpose — in which cargo residues, tank washing water, and ballast contaminated with cargo are retained on board. MARPOL Annex I introduced mandatory slop tanks on crude oil tankers to ensure that oily residues do not leave the ship until they have been separated and the water portion meets the 15 ppm discharge standard. The oil content of slop-tank water is monitored by the Oil Discharge Monitoring and Control System before any overboard discharge is permitted in open sea areas outside special areas.
Slop management requires careful stratification time before the water underrun is discharged. Officers record every slop tank transfer and overboard discharge in the Oil Record Book Part I. At the end of the voyage the remaining oil-rich slop is either retained as a base for the next cargo on crude tankers, discharged to a port reception facility, or pumped to a shore terminal. Port state control officers pay particular attention to the slop tank records to detect patterns of illegal discharge, and discrepancies between oil received, cargo outturn figures, and slop volumes often trigger detailed investigation.