martin's marine engineering page logo


Cruise ship Disney Wonder leaving Vancouver for Alaska. June 2022, picture by Martin Leduc

Practical guidance on Oily Water Separator (OWS)

Authored, compiled by Martin Leduc
June 2017

In regular operation, MarPol regulations require that all ship's machinery space bilge water must be disposed of either by pumping to an approved reception facilities ashore, or by pumping through an approved Oily Water Separator (OWS), the clean water overboard, and retaining the oil on board. Permission and guidance to discharge overboard should be sought from the Chief Engineer, or senior operational engineer, prior to starting. In flooding or emergency situations, you can "break" MarPol rules.

General Engine Room guidance

Oily Water Separator

Operation of the Oily Water separator

All users of OWS equipment should read & understand the maker�s instruction Manual, and the relevant parts of MarPol, and the relevant company's guidelines (in SMS system) before using this equipment. Users should also fully understand the piping arrangements.

Starting OWS operation

Completing OWS operation

Over the years, I have created numerous ship specific operating procedure for using the OWS, here is one sample.

The Oil Record Book (ORB)

Most MarPol prosecutions are based on the presumption that that oil has been discharge overboard illegally, but it is very difficult to prove this. As a consequence, authorities frequently prosecuted on the ORB record keeping aspect. In other words, improper record keeping used in covering illegal discharge, is used to ascertain illegal discharges. So pay attention when filling out the ORB, what appears to you to be a simple mistake could be the subject of intense scrutiny.

Be accurate. All the required instructions in filling out the ORB are provided right in the front pages of the record book. Read these instructions and understand them, provide the exact details demanded. Don't add extra details, don't create new numbers for entries; just do what they want, no more, no less.

Numerous agencies provide guidance on how and when to fill out the ORB. In particular a template of typical entries is handy to have attached to the ORB. When landing waste ashore, receipts of these transactions should be kept in, or close to the ORB for scrutiny by officials.

Additional steps in preventing unnecessary scrutiny from inspectors

From a typical company Safety Management System manual

In the event of serious flooding, the Duty Engineer is to take the following action:

The Engineer is to ensure that bilges are pumped out regularly within current MARPOL, Flag State Regulations and Company procedures.

When necessary, bilges should be discharged to the bilge reception tank and overboard, through the oily water separator. The Oily Water Separator is to be maintained as per Manufacturer's instructions and Company's PM system.

Notices should be placed at point of operation with regard to current legislation as to operation and special areas. In all other cases, shore reception facilities must be used. Oily water separator discharge monitoring devices should not be tampered with and any defects reported to Operations department.

Additional reading

Valid HTML 4.01 Transitional Valid CSS (Level 3)