1. Bilge System

2. Function
To drain any watertight compartment other than ballast, oil or water tanks and to discharge the contents overboard
The number of pumps and their capacity depend upon the size, type and service of the vessel

3. Example
An emergency bilge pump is required for passenger ships but may also be fitted as an extra.
The bilge and ballast systems, while having two distinct functions to perform in the vessel, could be so interconnected that it is found advantageous to cover the two systems on the same arrangement plan.
(The same pumps are commonly connected to serve both systems, and the piping with its valve and fittings must be so arranged that each system can function without interference with the other.)

4. All bilge suctions must be fitted with suitable strainers, which in the machinery space would be mud boxes positioned at floor plate level for easy access. A vertical drop pipe would lead down to the bilge.
To enable the internal perforated plate to be cleaned when necessary, the lid of the mud box is easily removed without disconnecting any pipework.

5. At the end of the bilge lines in other compartments, ordinary box strainers or their equivalent are satisfactory provided they have an open area not less than three times the area of the suction pipe.
A non—return valve should be fitted to the end of the bilge pipe in the compartment which it serves.

6. The bilge pumping system must be capable of dewatering the ship under all practicable conditions
A casualty including extreme conditions of list and trim
For this purpose, wing suctions are generally fitted
The piping design must be such that miscellaneous water in the compartments will drain to the bilge suction pipes.

7. The pump discharge
Each pump may have a separate discharge through the side
but it is desirable that the shell penetrations be as few as practicable
therefore, two or more discharge lines are usually combined in one outlet, each line being fitted with a valve to permit isolating the line from the others.

8. Bilge pumping systems are arranged so as to prevent oil or water from passing into spaces or from passing from one compartment to another.

9. MARPOL(marine pollution) or International Convention for Prevention of Pollution From Ships
Oil pollution at sea is limited by MARPOL 1973 legislation which effectively states that: It is an offence to discharge bilge water contaminated with more than 100ppm (parts per million) in some areas only 15ppm fuel or lubricating oil in a prohibited zone.
The international oil pollution chart shows the prohibited zones but generally it includes all waters within 160 km of the shore including territorial waters.
Oil/water separators are used to ensure that vessels do not discharge oil when pumping out bilges, oil tanks or any oil—contaminated space.

10. Large small craft (20m and above) are today often fitted with bilge water separates to ensure that any bilge water discharged conforms to the regulations regarding purity. This is particularly applicable to vessels operating in American waters covered by the U.S. Coast Guard Regulations
There is no doubt that the web of these regulations will be extended and tightened in an international effort to curb pollution at sea. Therefore we may be assured that in future Bilge Separators or Bilge water filtration will be a compulsory fitment in vessels of all sizes in future.

11. Specific requirements regarding the number of bilge pumps and their — capacities are delineated in the regulations.