If you own a boat, you’re going to face bilge pump problems sooner or later. Three years might be the average lifespan of a typical bilge pump before problems or obvious replacement needs arise. You can either spend the time off the water and money for the marina or dealer to fix it, or troubleshoot and replace it yourself. If you do it yourself, there are a few things to keep in mind for safety.
Here’s a true example of a bilge pump accident waiting to happen. A 21′ center console boat owner with a Johnson 1600 bilge pump found that his pump was blowing the specified 10A fuse. He replaced it with a 15A fuse and thought he solved his problem. The fuse was no longer blowing, but then he had a nagging suspicion that he had not addressed his problem correctly. What should he have done?
Thinking Through The Problem
A good place to begin is to think carefully through the situation, since it involves below-deck electrical systems. A wise starting point for me is to check the specifications for the pump, which are in this case:
Current draw: 7 Amps at 12 Volts DC
Fuse: 10A, 12V
Capacity: 1600 GPH (straight); 1550 GPH at 3 ft head
With the specs in mind, I can assemble my thoughts:
My thought #1: If it did ok for a while with a 10A fuse, but now needs a 15A to keep from blowing, why is this?
Answer: The pump or the conductor serving it must be pulling more than its rated current for some reason.
My thought #2: What could be causing the elevated current draw?
Answer: The pump motor’s field could be shorting out, there could be a flow restriction, there could be failing bearings or there could be corroded connections serving the pump.
My thought #3: If inspection of the inlet, impeller and outlet hose rules out a flow restriction from fishing line, debris, etc., then there could be something internally wrong with the pump, the conductor or the connections.
Answer: I should pour some water in the bilge and run the pump to see if its housing is heating up and/or if the conductors serving the pump are getting hot.
My thought #4: If the pump and conductors are heating up with a 15A fuse, this is dangerous, especially if the conductor AWG is rated for a maximum 10A circuit. There may be enough current to melt the insulation and metal connectors. I should also remember that degraded wires will introduce DC current into bilge water, resulting in accelerated corrosion of any metal fittings in contact with it (stray current corrosion).
My thought #5: If melting occurs, bare copper could short to something bonded to the grounding system, which would constitute a fire or explosion hazard in the presence of fuel fumes. This would not be good!
Responding Correctly
How many violations can you spot in this bilge pump wiring? (photo courtesy of BoatUS.com)
Answer: (1) No apparent in-line fuse of any kind. (2) No heat shrink tubing over the butt splice connector between the red (+) wire and the brown wire going to the float switch. (3) Wire nut used to splice the switch wire to the pump. Wire nuts should never be used on boats. (4) Hot wire is allowed to droop into the bilge water–possible source of stray current corrosion if insulation becomes damaged by heating.
Having thought through the situation, I am ready to respond intelligently.
Correct response #1: I should take out the 15A fuse and put the 10A fuse back in.
Correct response #2: If the conductor and its terminals look overheated or corroded, I could try first rewiring the pump with the correct conductor (braided, tinned, #12 or #14 AWG wire depending on run length). I should not use solid wire or non-tinned wire. Vibration and corrosion are not my friends.
Correct response #3: I should use marine-rated crimp connectors with heat-shrink tubing, installed using a correct ratcheting crimping tool for insulated or noninsulated terminals, depending on what terminals and heat shrink method I are using. I should not use a cheap, automotive-type crimper.
Correct response #4: I should install nonconductive restraints spaced no wider than 18 inches and enough wire length to keep the wire run out of normal nuisance-type bilge water collections.
Correct response #5: I should apply dielectric grease or other suitable corrosion inhibitor to all screw-on connections.
Correct response #6: With the pump back in service, I should check the temperature of the pump and the conductor after a long pump-out run. If the pump and/or the wire are warm, it’s probably time to connect my new wire to a new pump.
Also, I should remember that a bilge pump is meant to remove only nuisance water that reaches the bilge through small above-deck passages, not hull breaches. I must have access to all through-hull fittings, even if I have to cut my beautiful deck and install access ports. I should make sure that every through-hull is in good condition and fitted with a shut-off valve. I cannot depend on my bilge pump to keep me from swamping or sinking in case of a hull breach.
I should also tell myself that the sizing of my pump is important. The greater the height from the pump inlet to the hose outlet overside, the lower the capacity will be. In the case of the Johnson pump, a 3-ft head to the outlet downgrades the capacity from 1600 gpm to 1550 gpm. I will also incur capacity losses based on the number twists and turns of the outlet hose and also the pressure losses resulting from its corrugated profile.
The Rest Of The Story
The Marine Electrical Systems course enables you to maintain and upgrade your boat without depending on dealers, marinas or repair services.
So, what did our friend do about his fuse? He put the 10A fuse back in and bought a new pump. Wise skipper!
You might ask, “Where can I learn about these kind of things so that I can maintain and upgrade my boat electrical systems myself, safely and correctly?” Consider our Marine Electrical Systems course and let us know of your interest by submitting a Contact form.
