• A Centena Group Company

Monitoring and Control System


Polluting the oceans with oil from the ship is an environmental offence. Oil discharge monitoring and control system is the marine equipment used to check oil discharge. Automatic as well as manual monitoring can be done for this.




Our environment is getting worse by each passing day. We are witnessing a massive environmental degradation.  With the alarming rise of marine pollution, the maritime industry is under close scrutiny. Oil tankers carry different type of oil in their cargo tanks and they are discharged in a different port. Often the oil tanker needs to sail without the cargo. In order to do so, the ship takes a ballast from sea to get better stability of the ship. The ballast water is taken into cargo tanks and spilt out before the next refill. Oil discharged along with water is one of the main concern of marine pollution. Therefore, oil discharge monitoring and control system(ODMCS) is used to prevent the pollution of the ocean due to ships.


ODMCS (Oil discharge monitoring and control system) regulations:


1.       Oil tanker 150 GT and above, It ensures that any oily mixture discharged into the sea after passing the system has an oil content not exceeding 15 ppm.

2.      It is also to be provided with alarming arrangement & automatic stopping discharge system.

3.      When the oil content exceeds 15 ppm the oil shields discharged by the system is not to be seen by the visible      eye.

4.      Oil tanker 150 GT and above shall be equipped with an ODMCS approved by the administration.


ODMCS essentially consists of 4 parts. An Oil content meter analyses the content of oil in the water that is discharged. The quantity of oil is measured in parts per million. The flow of oily water is measured using a flow meter at the discharge pipe.  A computing unit calculates the oil discharge in litres/nautical miles along with the date and time identification. The ODMCS comes with an onboard value control system which is used to control the limits of discharge.


The oily water is discharged to the sea using a pump. A sampler probe along with flowmeter is connected at the discharge pipe, before the overboard valve, to sense the oil content and the flow of the mixture. The discharge valves are controlled according to the data provided by the two sensors. The valves will be automatically shut if the control unit senses a rise in ppm and open the recirculation valve which is connected to the slop tank of the ship.


Regulatory requirements for oil mixture discharge from cargo space


  • Tanker vessel must be en route.
  • The vessel should not be in special areas.
  • The tanker must be 50 nautical miles away from land.
  • The instantaneous rate of discharge of oil content does not exceed 30 litres per nautical mile.
  • The total quantity of discharge must not exceed 1/30000 of the total quantity of the residue formed cargo.
  • The tanker must have operational and approved ODMCS.


Manual Monitoring Procedures


The manual monitoring of the discharge needs to be done during daylight hours using Oil/water interface detectors. It is recommended to check ODMCS manufactures instructions for manual operation together with the procedure recommended by the Marine Environmental Protection Committee.108(49), as amended, as follows:

  •  Oil content meter or sampling system: location and measurement of the oil/water interface using the equipment as required in MARPOL Regulation I/32, visual observation of the surface of the water adjacent to the effluent discharge and recording the relevant data in the Oil Record Book Part II in sections H and I;
  •  Flowmeter: pump discharge characteristics such as the gallons or litres per minute to be considered in the calculation and recorded to check the accuracy of flow meter;
  • Ships speed device: main engine revolutions per minute as well as the propeller diameter, pitch and slip to confirm ship travel in nautical miles to be recorded;
  • Processor: manual calculation and manual recording of oil content vs. water outflow to confirm total outflow; and
  • Overboard discharge control: manual operation of pumps and valves to be utilized together with all the above to confirm that an instantaneous rate of discharge of oil does not exceed 30 litres per nautical mile.


The discharge must stop if there arises a concern or failure with ODMCS and the entry must be made in the Oil Record Book. The port State of destination, the classification society and the administration should be immediately notified via fax, email or phone in case of an ODMCS failure. The shipowner and the operator should be notified immediately and immediate measures need to be taken.