Oil Discharge Monitoring and Control System

The Oil Discharge Monitoring and Control System is mandatory under MARPOL Annex I for crude oil tankers of 150 gross tonnes and above and for other tankers of 400 gross tonnes and above. The system continuously measures the oil content of the overboard discharge from the cargo pump room bilge or the slop tank underrun, calculates the instantaneous rate of discharge in litres per nautical mile, and automatically stops the overboard discharge valve if either the instantaneous rate or the total oil discharged exceeds MARPOL limits. The system is type-approved to IMO Resolution MEPC.108(49) standards. The ODMCS flow meter, oil content meter, position sensor, and ship speed input must all be operational before any discharge commences. System malfunctions must be recorded in the Oil Record Book Part I together with the corrective action taken; discharges during system downtime may attract close scrutiny from port state control officers. Chief engineers are responsible for calibrating the oil content meter using standard solutions at prescribed intervals and for retaining calibration records. Data logged by the ODMCS — often on a data logger or electronic record — is increasingly used as forensic evidence in environmental prosecution cases.