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September 2010

Searchlight Feature - 16th September 2010


O.W.S’s have become a major piece of a vessels equipment due to the amount of bilge water produced on a modern vessel and the liability of severe consequences if this equipment fails to operate or if, for some reason, ships staff either bypass or attempt to bye-pass the equipment. Any indications that this equipment has been bypassed or attempted to be bypassed can lead to heavy personal fines and prison sentences for the responsible Master and / or Chief Engineer and even heavier fines for the ship owner or ship management company involved. With such risks then why would a C/E knowingly attempt to do such a thing? Ships senior officers are as environmentally conscious as any of us, if not more so, and very few would even consider such actions. Have we ever stopped to ask these people the real reason why such an act be considered or do we simply castigate them and pore scorn on such actions without really investigating the reasons why!

The true reason may be that static O.W.S.’s simply do not work very effectively. With the mixtures of chemicals, oils and emulsions which can be present nowadays in a ships bilges and the fact that ‘oil monitors’ do not actually detect ‘oil’ the efficiency of a static OWS is doubtful at best. In an effort to improve this equipments performance (and stay in the business!) suppliers of such separators add emulsion breaking Units (EBU’s) to their necessary equipment list. These EBU’s are “add on” units and have varying degrees of success in handling emulsions. There is a cost both in labour and materials in maintaining EBU’s in effective operation.

Bilge Handling System

In order to effectively handle the fluids and mixtures in a vessels engine room bilges it may be prudent now to fit centrifugal separators and a clean bilge tank – many cruise vessels are now doing this but the latest legislation will need to be additionally checked to confirm what can and cannot be done (Carmania are in the process of doing this). We must consider the bilge handling as a whole and not the OWS in isolation. On many vessels over 80% of the ‘bilge water’ may be considered pure water – this includes water from the main engine scavenge air coolers drains taken from before the separators (this constitutes the largest percentage of clean bilge water), drains from the fridge and A/C save-all’s, the HT and LT cooler save-all’s, FWG save-all’s and boiler drains! Such drains as these would be better being piped to a separate clean bilge holding tank from where they can be pumped directly over the ships side – should this be approved by Flag and Class - or treated differently from the bilges whose contents are or could be of suspect condition. An oil detector unit could be fitted in the clean bilge holding tank as an added precaution. It seems somewhat self defeating to mix known clean bilges with bilge water of suspect condition and then put the complete contents through a very difficult process and therefore risk unnecessary and increased oil contamination and give the ships staff the near impossible task of treating a larger quantity of water than necessary through this difficult process.

It has been claimed that use of centrifugal separators for the purpose of separating oil from water can result in water discharge with an oil content of less than 5ppm. The claims seem to be substantiated from discussions with, and by reports from vessels that operate such systems but to be fully successful a clean bilge tank is necessary and a de-aerator is needed to remove the entrapped air from the cleaned water prior to it going through the oil monitoring unit. Since the oil monitoring unit detects the opaqueness of the water, not oil the de-aerator is vital to clear the water of this air. The suggested modifications will need to be discussed with Class and if the mentioned clean bilges cannot be pumped directly to sea at least they should go to a separate tank, in which case the handling of these clean bilges by the separator will be much easier than mixing them with dirty water prior to going through the separator.

Options of Choice: One should not underestimate the serious nature bilge handing has acquired due to all the legislation on the limitations of pumping bilge water overboard through the oil content monitors.

If you are considering a change out of your existing OWS and / or looking into your bilge system as a whole Carmania can assist you with project management, from choice of options, selection of equipment, planning the modifications, Class and Flag approval through to supervision of installation work.


We sort the opinion of DNV on the subject and (while we respect the fact that DNV must remain neutral on the issue which brands do and don’t perform beyond the fact that the OWS must be type approved acc. to MEPC. 107(49)) they did have some interesting news for us. During 2011 DNV expects to introduce a brand new type approval regime for 5ppm OWS and 5ppm alarm systems. It is expected that only the absolute best OWS and 5ppm alarm systems will cope with new strict 5 ppm requirements, and this might be something to look for when purchasing new 5/15 ppm OWS and 5/15 ppm alarm system equipment. Additional reading on the subject of this bulletin article can be found in the June 2010 issue of Motorship.

About the author:

The author of this article is a chartered marine engineer with a combined Certificate of Competency and over twenty years sea service including over a decade serving as a C/E on cargo vessels, container vessels, specialized vessels (including large private yachts) and oil tankers. He came ashore to take up the position of superintendent and continued his career progression to ultimately fleet manager in which capacity he has served, with two Companies for a period of ten years. He is now continuing as an independent consultant. Apart from the usual daily operation of vessels of many kinds he has been involved in many projects often leading a team of engineers on major projects.

During the earlier part of his sea service it was usual practice to change over fuel on main engines for manoeuvring to gas oil / diesel oil and as a second engineer and C/E he always encouraged junior engineers as well as the senior engineers to become familiar with this routine. During his career as C/E he served on ‘’special vessels’’ where all power plant was operated using gas oil, i.e. - main and auxiliary engines and boilers. In early 2009 as manager he was asked to look into the feasibility of operation of VLCC plant to meet the Californian Air & Resources Board (CARB) requirements of using distillate fuels on the U.S. west coast – which become law on 1st July 2009.

He continues his career in the industry taking a keen interest in the development of new legislation and the implementation of recently agreed requirements, some of which is not always in the best interests of the industry and some of it is, unfortunately, politically motivated.