Introduction To Bilge System

Introduction To Bilge System

Bilges are the lowest part of the ship, The water which collects here is called bilge water, Which includes any wastewater that is generated on board the vessel.

bilge system

Where does Bilge water come from?

  • All machinery has trays beneath them with drains.
  • Like bathrooms in our homes, the engine room has several drains, which lead down to the bottommost part – that is bilges.
  • For example: if a tank overflows or a pipe bursts in the engine room, the liquid will finally end up in the bilges. This is an extreme example but there are several other ways of water leaking/ draining into the engine room bilges.

What are Bilge wells?

Bilge wells are the compartment located in the bilge area of the ship, i.e. the bottom-most part of the ship that is designed to collect and hold the wastewater that is generated on board the ship. These tanks are typically located at the lowest point in the bilge area to allow the wastewater to flow into the well by the phenomenon of gravity.

bilge well

In other words, Bilge wells are sumps into which the bilge water drains.

What do we do when the Bilge Holding tank fills up?

  • At the port, we can land it offshore at a barge/truck/reception facility.
  • At sea, we can discharge it overboard through approved Oil Filtering Equipment as per MARPOL Annex 1, Regulation 14 & 15.

What are the regulations for discharging Bilges?

The following are for machinery space Bilge for all ships above 400GRT:-

  1. The ship Should be en route which means the ship should be moving toward its destination, So she does not dump all bilge water in one single place.
  2. The oily mixture should be processed by approved Oil Filtering Equipment (Oily Water Separator)
  3.  The oil content of the effluent without dilution does not exceed 15 parts per million.
  4. Oily mixtures do not originate from cargo pump room bilges in oil tankers.
  5. The oily mixture in the case of oil tankers is not mixed with oil cargo residues.
  6. Discharge is prohibited in Antarctic areas.

Transfer of Bilges from Bilges well to Bilge Holding Tank.

The bilges from the bilge well transfer to a big tank called a bilge holding tank.

bilge passage

As per the picture, the bilge pump is running via two filters the bilge water or wastewater is transferred from the bilge well to the bilge holding tank.

What is Oil filtering Equipment and How the bilges were transferred overboard?

OWS or oil filtering equipment is used to filter out oil from bilge water before pumping overboard.

As we have seen earlier that bilge was transferred from bilge wells to bilge holding tanks.


Now, the bilge from bilge holding tanks is transferred via the bilge pump to the oily water separator and transferred overboard to the sea and if any oil contains remains it will be sent back to the tank with the help of the Oily water separator.


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