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 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.