Bilge System
The purpose of a bilge system is to remove unwanted water and other liquids from within the
vessel. The bilge system is used to remove small quantities of fluid that have leaked or
condensed into a dry space. The system serves the machinery spaces, cargo holds, cofferdams,
voids, stores, tunnels and pump rooms. Each space has its own piping but the pump is likely to
be shared.Bilge level alarms are fitted to many bilges, in particular the engine room bilges. The
audible alarm must have a power supply from both mains and emergency systems and the alarm
must be clearly audible to a person at the steering position under all operating conditions.
Requirements
Other than in vessels less than 7.5 metres in length, all vessels must have two bilge pumps,
which in vessels of up to 20 metres may be a combination of both power and hand driven.
Beyond 20 metres both pumps must be power driven and have different sources of power. Each
of these pumps will have a specified discharge capacity. A further requirement is that power
driven pumps must be self-priming or be provided with a suitable priming device.
All bilge suctions are required to be fitted with strum, strainer or mud boxes to prevent solids
from entering and either blocking or damaging the system.
Back Flooding
Back Flooding, where sea water from the sea suction floods back through the system into a bilge
space or water from one bilge space floods through the system into another, is not a desirable
situation and may lead to the sinking of the vessel. Back Flooding must be prevented at all times
and done automatically. This is achieved with the use of non return valves in each of the bilge
pipes which prevent flow back into the compartments.
Typical Arrangement
Figure shows a bilge system as fitted on a vessel of 20 to 25 metres in length. The system looks
similar to the ballast system except that the valves are mainly screw down non return as opposed
to screw lift. The sea water connection (No 4) acts as a primer for the pump and is used to flush
the system after pumping bilges. The forward bilge suction is not into the fore peak but into the
chain locker, whereas the aft suction is from the steering flat. Each suction is fitted with a strum
box (No 2) and a non-return valve (No 3). No 1 is a connection to the deck or it may lead to an
oil - water separator and slop tank. If the vessel is not fitted with a separate oily waste tank, the
oily bilges should be pumped into a large drum or container on deck for disposal ashore at a later
stage.
Figure - Bilge System
Common Problems
Mechanical Failure Of Pump
• Pump not turning - check power source switch is on and cable etc in good repair.
• If the pump is driven from an engine it is possible that the clutch is slipping or not
engaging properly.
• Flexible impeller pumps shed their vanes either through old age or having been run dry.
If this is the case then the impeller will need to be replaced according to manufacturer’s
instructions.
Air Leaks
This is a common problem on the suction side of the system and may be caused by:
• leaking glands on pump drive shafts
• leaking glands on valves or cocks
• Holes in the pipework caused by mechanical damage or corrosion
• Empty compartment valves being opened or leaking thereby drawing air into the system
Blocked Bilges
Strum boxes and strainers are provided to prevent foreign material such as rags and other waste
from entering the system. However, a blocked strum box in a flooded compartment may be
difficult to get at to clear hence, keep the bilges clean at all times. High level bilges can lead to
dangerous situations including:
• Free surface effect on stability
• Fire hazard due to oil in the bilges
• Dangerous and explosive gases from bilges
• Slippery and dangerous surfaces to work on
• Corrosion
• Oil and water getting on machinery situated lower down
• Effect on trim, heel and draft of the ship
• Cleanliness
• Impaired visibility of lower spaces covered by bilges
Regular User Maintenance
Cleanliness is the primary requirement for ensuring a bilge system is ready for operation.
A regular maintenance program should be implemented. The time interval will depend on the
type and usage of the vessel.
A typical maintenance program would be to:
• Keep bilges clean from rags and other foreign matter.
• Clean strainers.
• Put some water in each bilge well and pump out each in turn to confirm satisfactory
operation.
• Open up all bilge suction non-return valves in the system. Check the fit of the valve to the
seat to ensure it seals when closed.
