A dry bilge for $50

Water in the bilge, even small quantities, is a recipe for bad smells and generally unpleasant results. Every boat I’ve owned accumulated water somewhere that a traditional bilge pump couldn’t entirely remove. I’ve long been aware of commercial kits designed to completely dry bilges, but the problem never got high enough on my list to spend the money. Recently I came across an article on how to build your own dry bilge system and decided to give it a try. The results are impressive and the cost low.

The system consists of one or more homemade water pickups, a small (1.3 gallon per minute) diaphragm pump, and some plastic tubing. The author of the article used three such pickups and a small manifold before the pump. Have Another Day only has one area that typically has water and the rest drain back to it, so I only used one pickup, and thus didn’t have to construct a manifold or deal with differing tubing diameters as described in the article. But early on in my use, the pump became clogged with crud from the bilge so I added a small inline screen filter.

The pickup itself is an electrical plate cover, a sponge, and a 90-degree hose barb to threaded adapter. I drilled holes in the side of the threads on the barb adapter to allow it to draw water through the sponge. I also hollowed the sponge out for the barb adapter and then ran two stainless screws through the plate and the sponge to hold it together.

I used 3/8-inch inside diameter tubing and a 3/8-inch to 3/8-inch elbow of the pickup. The electrical plate cover I bought came with the little arm you see pictured that provided a way to anchor the micro-pickup to the main bilge pump’s plate. That arm and a few washers on the screw through the plate helped me force the sponge down to the bottom of the bilge.

Have Another Day’s bilge can hold many gallons of water and still be below the float switch’s trigger point

Have Another Day sits stern low so any water in any bilge area eventually makes it’s way back to the aft bilge. The float switch and bilge pump are mounted on a board raising them about an inch and a half over the lowest point of the bilge. The couple of inches the float switch needs to turn on combined with the raised mounting position mean that quite a bit of water can collect in the aft bilge and won’t be evacuated by the main pump. The dry bilge pump is able to get the bilge down to just a few drops of water, though it does take about 10 minutes to empty the bilge when it’s at the level in the picture above.

The author of the article uses a small timer to control his dry bilge system and that seems to work well for him. Never content with a simple solution, I got a little more involved in controlling my dry bilge system. Now the power is managed by a Maretron MPower CLMD12 digital switch with current metering capabilities. Knowing that pumps draw more power when they’re moving water than when they’re pumping air I figure it was likely I could use the CLMD12’s current metering to determine if water was still moving. It turns out the pump draws about 1.5 amps with water flowing and 0.7 amps when it’s just moving air.



I use SignalK Server and the Node-Red plugin to turn on the pump at 8pm every night and then watch how much current the pump is drawing. First, the node I defined lets the pump run for one minute. Then, if the pump has run for more than one minute and is drawing less than 0.8 amps, it’s turned off. Thus far this setup has worked perfectly to turn run the pump long enough to make sure the bilge is dry after each run.

I believe my total investment in this project is right around $50. I am leveraging other components already on the boat to control the system but if I didn’t have them I could easily use a timer or even just a toggle switch. Regardless of how it’s controlled, I can’t believe how easy and productive a project this was. I’ll reap the benefits of the small investment in time and money in the form of a drier, less stinky bilge for years to come.

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Ben Stein

Ben Stein

Publisher of Panbo.com, passionate marine electronics enthusiast, completed the Great Loop in 2017.

8 Responses

  1. Gary H Hagstrom says:

    Ben,

    Where did you route the discharge? It seems to me that is always a key issue for these systems. I hate to install more through hulls and combining discharges is also frowned upon.

    I would like to solve this issue on Crackerjack since it lies bow low so you have to lay over the engines to mop each hull dry.

    All the best

    • Ben Stein Ben Stein says:

      I was able to route into a deck drain elbow. It discharges well above the waterline already had a couple of drains meeting so I didn’t feel this was an unreasonable risk to take. I suppose it’s possible that if the discharge of the drain were sufficiently backed up it might drain towards the bilge but I’m not sure the pump would allow the water through and even if it did the main bilge pump would be able to evacuate the water. Plus if those drains backed up they’d overflow into the bilge as well so it’s effectively the same risk.

      -Ben S.

    • Colin A says:

      I would pump it into a cockpit near a cockpit drain myself, but that might annoy some people (stains etc). I have run similar ones into outboard motor wells before (thou those are less and less common). On some larger power yachts I have worked on I have seen the Arid bilge tied into sink drains well above the water line several times. A siphoin break above the sink would prevent most issues in that setup.

  2. Matt Byrne says:

    Since MIBS, I have been slowly working on this project too after seeing a COTS system that is sold by the pump manufacturer on Amazon for a very reasonable, though not $50 (!), price. Thanks for the thoughts on drain spots. That has been slowing me down. I am thinking about building another for my shower sump , which always has nasty water in it. Where did you find the filter? I am going with a timer (per article) but you now have me wondering about Rhasperry Pi for intelligence. I am never going to complete my boat to-do list.

  3. Scott Booker Scott Booker says:

    Same principle as the Rule 25SA 500GPH bilge pump that I have been using in my PWC’s for years. For me they have worked well, but they are susceptible to getting “crudded up”, which flummoxes the current-sensing. I’ll be interested to see how the long term reliability works out for you.

    Well done!

    • Ben Ellison Ben Ellison says:

      Looks like a nifty little pump…

      https://www.amazon.com/Rule-25SA-Electronic-Sensing-Bilge/dp/B0719D2HSX

      … but I don’t see how it could attain the same level of “dryness” as what Ben S put together.

    • Ben Stein Ben Stein says:

      You probably noticed the strainer style filter on the pump inlet; without that filter the pump tends to get jammed with debris. With that filter in place it’s been running for over a month without any issues.

      As for the current sensing side of the house I’m only about six weeks into running it but I’m very happy with how it’s working. Most nights it runs for exactly one minute. If I’ve done something in the engine room to spill a little water it might run slightly longer. I think I’m going to add a step to send me a summary email after the pumping session is over. That way I can know how long it ran and the current consumption over that time period.

      -Ben S.

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