Bilge pumps explained

Bilge pumps explained

The purpose of a bilge pump is to remove bilge water, which may contain oil, detergents, solvents and other chemicals. Find out more here about modern (electric) bilge pumps, which come in several guises.

Voltage is generally 12 or 24v DC power, although other voltages are available. Ensure your pump is wired to the live side of the battery master switch.

Bilge pumps with float switch

Some pumps need to be prompted to start/stop. Traditionally, this is controlled by a float switch: when the float rises, the switch turns on, and as the bilge water falls, the switch will lower and turn off the pump.

Electronic sensor switches

Electronic sensor switches detect the bilge water at a specific level. They have no moving parts to foul, so are likely to be more reliable than a float switch.

Pumps can be ‘dumb’ or ‘smart’.

Electronic timer sensing bilge pump

Dumb pumps need a remote (float) switch to work them. Smart (electronic timer) pumps pulse periodically (e.g. every two minutes), and if there is a water resistance the pump will kick into action. These pumps will use battery power continually, so make sure you have an on-board battery charger, and a plan for winter or when your boat is idle for months. Some pumps now have a built-in mechanical float switch or an electronic sensor switch. These pumps require less wiring, so installation is easier.

Typically, electric bilge pumps have outputs from about 1325 litres per hour to over 13250 litres per hour, with a variety of discharge hose diameters. Note the flow will be restricted when a smaller hose is attached.

Low profile (horizontal or vertical) bilge pumps are now on the market and can be useful where space is tight.

Bilge pump tips

  • Always mount your pump in the lowest part of the bilge
  • You may need multiple pumps for compartmentalised boats
  • Adding non-toxic anti-freeze in the bilge will prevent water from freezing (and impacting the pump) in winter
  • Some waterway authorities, including the Environment Agency, now insist on installation of a bilge pump filter system to prevent oils from being discharged overboard
  • Regularly inspect and maintain your bilge pump. If you do not have the luxury of shore power, consider a solar powered battery saver. The smallest will usually keep up with a bilge pump.

Buy Jabsco and Seaflo bilge pumps, switches, filters from our online chandlery.

Interesting fact: historically, sea water sucked in by bilge force pumps was used to preserve live fish in onboard tanks before ships docked.

Back to blog