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How To Replace A Bilge Pump


Often forgotten, the bilge pump is a vital piece of equipment on your boat. If yours is on the fritz, here’s how to change it out.

Unloved and neglected, the bilge pump sits forgotten until the day it’s called upon to pump water out of the boat. Except that sometimes they don’t work as they’re supposed to.

Use smooth-bore hose rated for the purpose between the pump and the outlet. Although easier to install, corrugated hose causes turbulence within it, severely reducing the output capacity of the pump. Also, avoid sharp bends and low spots in the hose.

Bilge pumps rely on electricity to work, but the damp confines of the bottom of the boat conspire to corrode cables and pump components, rendering them useless. It pays to check the pump’s operation regularly, but they have a finite life, so if yours is dead, here’s how to change it.

Technical Support

Degree of Difficulty: Easy to moderateTools and Materials:

  • Screwdriver
  • Electric crimper
  • Pliers
  • Drill
  • Wire stripper
  • Pump
  • Marine-rated sheathed electrical cable of gauge ­required by pump and wire run length
  • Hose clamps
  • Mounting ­hardware
  • Heat shrink crimp connectors

Time: Depends on size, type, and placement. An hour is typical.

Cost: $100 approximately, ­depending on pump.

1. Before you rip out the old pump, check that it truly is the pump that’s dead. Try the manual override at the helm, and lift the float switch in the bilge. If operating either of these fails to turn on the pump, then the pump’s mostly likely in need of replacement. But first check to see that the fuse (or circuit breaker) is OK and the battery is charged. Also, check that the circuit to the pump is OK by using a volt/ohm meter at an appropriate location, typically at the wiring connection immediately above the pump.

2. Most bilge pumps are wired directly to the battery. This allows the pump to operate even when the boat is left unattended or the main battery switch is off. Either disconnect the pump wires from the battery or disable the inline fuse (as shown) or circuit breaker.

3. Disconnect the hose from the pump body by loosening the hose clamp and pulling the hose clear.

4. Next, cut through the wires just above the existing connections. In most cases, there will be three wires. Make note of the wires on the new bilge pump that must correspond to the existing wiring.

5. The exact mounting method varies by manufacturer and size of pump. In this case, the pump was screwed to a pad fiberglassed into the bottom of the hull under the engine. With the pump out of the way, I was able to unscrew the two stainless screws that retained the strainer to the bottom of the boat.

Install a larger bilge pump than you think you’ll need because the stated output is only under perfect conditions. For every 3 feet of lift, the output is halved.

6. Use new screws to secure the pump in place. Be certain as to what you’re doing. Don’t drill through the bottom of the hull! Most boats have a mounting plate for the pump, but if you’re at all uncertain, seek expert help.

7. Make new electrical connections using new crimped connectors covered with heat-shrink tape.
 This will keep water out of the connections and prevent electrical leakage into the bilge water should it rise that high. This could discharge your battery or cause stray current corrosion. The end of the wire from the pump to which you connect the ship’s wiring should be well above the bilge high-water level and away from stuffing box splatter to further avoid corrosion. You may need to use additional marine-rated sheathed electrical cable, splicing it with appropriate crimped connectors with head shrink tape. Tie off the wiring if needed, to avoid it getting caught in moving parts.

8. Finally, reconnect the discharge hose to the pump using a new hose clamp. Then test the pump and switch for operation by putting a few buckets of clean water into the bilge. There should be good stream of water coming out the outlet. If your automatic switch is an external float switch (separate from the pump housing), check to see that it works by lifting it up.

Mark Corke

Contributing Editor, BoatUS Magazine