The Offshore Voyaging Reference Site

The World’s Best Bilge Pump Switch

Peter, a reader and member, related a tale of frustration with a bilge pump switch in this comment and that got me thinking about a great piece of gear that we have used on Morgan’s Cloud for over 20 years without one single failure or hint of a problem:

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Peter Naumann

Hi John

I wanted to share a recent unusual incident, with a bilge pump.

I recently fitted a new automatic bilge pump to my Catalina 309; a Rule-Mate 1100. All went well for the installation and pump worked well.
However, soon noticed the pump failing to turn off; but by switching to off then back to auto it stayed off and seemed to come on again when needed.

Yesterday decided to look more closely. I cleaned the bilge so thoroughly you could eat dinner off it and washed out the bilge pump. Using a hose I tested the pump and while at first spluttering a bit – perhaps due to soap – it was working well and switching off automatically as expected. I tested it on and off for about 5 cycles to rise out the whole bilge. Then refitted all.

Now the mystery.
Today when I returned and the pump was running again having failed to switch off. I thought I must just have a faulty pump and would replace it. But before i cleaned it all again – using the freshwater hose. AND magic – it turned off automatically every time. In fact it did this 3 or 4 more times.

I then pumped out and tested it with a bucket of clean saltwater. It failed to turn off!

It seems to me (I have yet to pull bilge pump to bits as it is all sealed) that there is an electrical switch inside the pump that makes contact when water covers it. However, as salt water is more conductive it seems that a very small amount keeps the connection active and so the pump does not respond and switch off.

I have written to Rule Inc the manufacturer of the pump but am yet to hear back.

Keith Jones

Hi John,

On Pearl our Bristol 45.5 the deep bilge is below the engine and the switch must slide into a narrow space mounted on a piece of aluminum stock. I used a 2 prong electronic switch for a number of years but one failed after about 8-9 years, but those are no longer made. About 5 years ago I replaced the switch with a Water Witch which has a great reputation and has been working well.

This switch is connected to a diaphragm bilge pump with a counter, if water gets above the “deep bilge” then there is another switch attached to a high volume submersible pump and an alarm. That pump should be replaced so it will be interesting to read your upcoming pump post.

I do think that a bilge pump cycle counter is an important safety feature, plus when I recommission the fresh water system I can figure out if there is a leak.


I see the “Water Witch” pump switch mentioned above. My experience with it about six years ago: placed it in my cockpit while I was doing work on cockpit drains, in order to pump out any rainwater that collects.
It failed to pump, so I took it back and got a replacement – failed again. Turns out that it switched fine with salt water or dirty water, but pure rainwater is less conductive and thus it would not trigger. A work-around would have been to sprinkle some salt in the cockpit while the drains were closed. So the exact opposite of Peter’s experience (see Peter’s comment above).

Larry Clough

I went through multiple “Water Witch” pump switches that failed over a three year period before finally giving up and getting an “Ulta” which has worked flawlessly for the past two years.

Bob T.

I agree with Johns assessment of this USS switch, the SR version comes with a lifetime warranty. I have two of theses stacked with the higher one used to trigger the high water alarm and pump. The lower controls the regular bilge pump. Both pumps are controlled by programmable relays that delay both the on and off functions preventing unnecessary cycling and assuring a completely dry bilge. John is correct the bilge alarm will wake the dead.

Steve S

Our experience after 25 years running private yachts: The only “forever” pump switch we have experience with is the “Ultra Pumpswitch” by Ultra Safety Systems. We have (8) of them on our current vessel, they work without fail in all conditions (we test all of them on the 1st of every month). They are not susceptible to failure from fresh/salt/oily water, and are offered with a built in high water alarm trigger. We have had more than (50) of these units in service on various boats over the years, I have never seen or heard of one failing.

The following failures have been witnessed with a couple other common brands:

“Rule” float switches eventually absorb water and fail. The wiring gland also leaks and corrodes the wiring internally (ensure your connections are as high above bilge water as possible and totally waterproofed by heat-shrink connectors covered with additional heat-shrink tubing). These switches seem to last about 3-6 years. The “Plus” model lasts about 50% longer, but do eventually fail in the same manner. We destructively test these after they fail to satisfy our curiosity regarding the point of failure.

The “Water Witch” has proven unreliable in the unclean “real World”, usually due to oily residue in bilge water. If any oily residue is found on the contacts, the switch becomes unreliable.

We have also used “Tank Sentry” units to monitor tank/bilge level and trigger pumps for transfer (fuel day-tank) or discharge (bilge/black/grey water). This type of system (small air pump blows air through a sensor tube, then measures pressure of fluid level coming back up the tube) have been basically reliable with one exception: in grey and black water tanks (or dirty bilges I suppose) the small sensor tube eventually gets fouled by solids in the fluid and requires compressed air to clear the tube. In black water tanks this fouling happens as often as monthly; grey water tanks quarterly; potable water and diesel basically never. Other than this routine maintenance, they have proven reliable (the little pump sounds like a mini-jackhammer, Guests complain about the noise when trying to sleep).

We use the Rule automatic bilge pumps in our Tenders with good results. The resistance based sensing of these pumps seems simple and has proven reliable….but for proper de-watering protection on large boats, we stick with large pumps (AC and DC) with short and smooth plumbing runs, triggered by Ultra Pump Switches.


Svein Lamark

Well John, I think you can get better pump switches/high water bilge alarms than Ultra Safety Switches. Look at The Kirk has no electronics in the bilge, only a pipeline down and the sensors and electronics are sitting far above the bilge. The Kirk system will normally last longer than those switches sitting in salt water. The Kirk is the Rolls, but also Johnson and Hydro have this kind of technical solution at a much nicer price. I think all tree of them are better and safer than the Ultra Safety Switch according to my experience. Electrical parts in salt water are often problematic. I have had all of the switches in fishing boats with a lot of debris in the bilge water. The problem is than not the switch, but debris coming into in the pump. The Kirk pump can take a lot of debris, but a cheap sewer pump (Jonson) sitting far above the bilge water will solve the problem of debris in bilge water. The Kirk pump can sit 2 meters above the bilge and lift 5 meters. I think the best system is a Johnson sewer pump at a low level and a Kirk system a bit higher up. The Johnson can take the debris and the Kirk has the lager capacity in case of a lager leak.

Marc Dacey

I have a Rule 3700 down our deep steel bilge at the moment, which is bone-dry thanks to the PSS Shaft Seal, but I very much enjoy hearing about these sort of lesser-known solutions, and I will improve on that Rule with an alarmed “high/low” setup of two pumps should ingress become an issue. On my other boat, which has a traditional stuffig box, I naturally get water (a few cups) in the bilges, and have had difficulty finding a pump that lasts more than a couple of years. The latest one,a Whale 650, seems dead…lucky I never removed the old Whale Gusher manual pump…


I just in stalled a Ultra Mini. For the price, I was very surprised that tinned wire is not used…particularly for a bilge switch. Yes I know … adhesive lined heat shrink terminals are required / used. I still don’t think non-tinned wire on a bilge switch is acceptable.

William Murdoch

The image of the Ultra Safety Systems high bilge water alarm shows a three position toggle switch; test / mute / on . I had similar when we bought our PCS 34. It was, unknown to me, in the equivalent of the mute position. The second night of our ownership in a marina, I popped out of the v-berth on a cold November morning into frigid water over my ankles and our shoes floating about. Luckily, I could still hear the water running into the boat and got that stopped. My bilge alarm now has just two positions, on and mute, and there is a red cover over the toggle switch like the ones you see in the movies just before they drop the bomb. To mute the alarm, I raise the red cover and flick the switch. Closing the cover returns the switch to the on position covering it and preventing its being accidently knocked into the mute (off) position. I test the alarm by flooding the bilge or raising the float. That tests the whole system, not just the howler.

Mine is the same as this one, but reverts to ON when closed.