Build Your Own DIY Arid Bilge or Dry Bilge System

Manual and automatic bilge pumps, whether submersible centrifugal pumps or remotely mounted diaphragm pumps, cannot completely clear a bilge of water.  Typically 1-3″ of water remains.  In a shallow bilge boat like the Catalina 25 used for this prototype system, this can lead to a substantial volume of water remaining in the bilge.  Water in the bilge can cause serious problems on many boats, including causing wood stringers to rot and internal fiberglass blistering.  Bilge water is also the primary source of that distinctive “boat smell”.

At the time of writing, there are two commercially available products that address this problem, with advantages and disadvantages compared to this DIY system.  The Arid Bilge system is a smart, but relatively expensive system.  The more recently introduced Dry Bilge system is smart, but less so than the Arid Bilge, and is much less expensive.  The Dry Bilge system appears to leave more water in the bilge than the Arid Bilge system, and appears less robustly constructed than the Arid Bilge system.

Both of these commercially available systems are intelligent, only operating their pumps when water is detected in the bilge, which results in less power consumption.  As a less intelligent and much less expensive alternative, this DIY system runs on a programmable timer, which draws power on a schedule regardless of whether or not water remains in the bilge.  Both of the commercial systems appear to not remove the last remnants of moisture from a bilge because they do not use sponges, and appear subject to clogging at their water pickup points.  This DIY system can remove the last remnants of moisture from a bilge, does not tend to clog, and costs less than $100.

This DIY system starts with common household sponges, which absorb moisture in the bilge areas.  The moisture in the sponges is sucked through small feeder tubing, leading to a simple suction manifold, with the suction generated by an inexpensive DC-electric diaphragm pump.  The discharge from this pump can be plumbed into the manual bilge pump outlet hose near where it drains to the through-hull at the transom (Plumbing to the hose near the through-hull at the transom may be considered important for safety.), or routed to the lifting cable through-hull on swing-keel boats.  The pump is controlled by an inexpensive DC-electric programmable timer, which can be installed on the electrical panel bulkhead.  For the prototype installation, the timer was programmed to engage the pump for two minutes every six hours, which resulted in a completely dry bilge in all seasons and weather, regardless of leaks and sailing conditions. In this case, the programming could be changed to pump less, such as for two minutes every twelve hours or one minute every six hours.

In many boats, there are separate bilge areas in which water typically collects.  For the prototype system, there is a separate pickup in each of these areas,  a total of three pickups for the system.  There is one pickup beneath the forward v-berth, accessible through the wooden hatch beneath the v-berth; one beneath the starboard salon floor, accessible through the small wooden bilge access panel; and one beneath the port salon floor, accessible through the large wooden bilge access panel.

Regarding ongoing maintenance, the pickup sponges need periodic replacement when they begin to deteriorate, at least annually in this prototype system.  Allowing the sponges to deteriorate could cause the tubing to become clogged with sponge debris.

A note about pickup-to-manifold tube sizing:  four different internal diameter tube sizes were tested, 1/16″, 1/8″, 1/4″, and 3/8″.  The 1/8″ internal diameter tubing yielded the greatest volume of water removed when one of the sponges was wet while one of the sponges was dry, which is likely to occur in this system.

Parts:

  • Seaflo 1.2gpm diaphragm pump, available from Amazon.com
  • Generic 12v DC timer, available from Amazon.com
  • 3/8″ clear vinyl tubing, available from most hardware stores, used for manifold, and inlet and outlet to pump
  • Rubber stopper, available from most hardware stores, used  for capping end of 3/8″ suction manifold
  • 1/8″ clear vinyl tubing, available from most hardware stores, used for line from pickups to suction manifold
  • 1/8″ to 3/8″ plastic barb fittings, available from most hardware stores, used for sponge pickups, and at suction manifold
  • Household wall faceplates with center hole, available from most hardware stores, used for mounting sponge, and holding plastic barb ttings to 1/8″ tube
  • #12 fine thread stainless steel screws, available from most hardware stores, used for mounting sponges to faceplates, and mounting pump to bulkhead
  • #6 stainless-steal through-bolts with nuts, available from most hardware stores, used for mounting timer to electrical bulkhead
  • Cable ties, available from most hardware stores, used for mounting tubing to existing systems
  • 16 gauge wire, available from most hardware stores

A version of this article originally appeared in the November 2017 Catalina Yachts owners’ magazine, Mainsheet.

27 thoughts on “Build Your Own DIY Arid Bilge or Dry Bilge System

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  1. I really like this setup, I have always wanted the Arid, but it is so much money for just a fancy wet vac. My only concern is I am mounting the DC timer in the engine room, does that need to be ignition protected?

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  2. This is fantastic! Just followed your steps for my forward berth; bone dry!

    Quick question… When using three pickups on a single pump, did you have any issues where the pump would draw 90% air vs water from another compartment? (Since it’s easier to lift air than water?)

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    1. Hi Dave, that certainly could be an issue for you. I tested four different tubing diameters: 1/16″, 1/8″, 1/4″, and 3/8″. In my installation, I found the best performance with 1/8″ tubing. The larger diameter tube would draw too much air. The smaller diameter hardly moved any water.

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  3. Thanks for creating this. I’ve had this issue on 2 boats and looked at the Arid system for years but price keeps me away. How did you secure the sponge? I’ve been testing the system out and understand why you use the 1/8″ tubing, great idea!

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    1. In the test installation, the sponges did not need to be secured to the bottom of the bilge. The sponges naturally rested in place when wet by capillary action against the bilge, and when dry simply by gravity.

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      1. Great system. I’m just building one now.
        One question… would it be better to have the pump nearer the bilge or closer to the thru-hull? There’s not much lift required, about a foot or so, but the run between the two is about 10 feet.

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      2. Thanks. It shouldn’t matter too much with that short of a run from the pickups to the thru-hull. Theoretically, the system should pump better with shorter pickup tube runs due to the narrower diameter of the pickup tubing compared to the outlet diameter.

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  4. Hi, I did this project and works great for one bilge however, when trying to add my other 2 bilges if any one of them dont have water in the bilge they suck air and none off them work. Any ideas? add ing a pump to each bilge isnt an option because they arent igntion protected.

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    1. What size tubing did you use for the pickups? How far is each run to the suction manifold? You could try a smaller diameter tube for one or more of the runs from the pickup to the manifold. For a bilge area that is usually wet, you also could try larger diameter tubing.

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  5. I “stole” your idea and created a very similar system on my Catalina 470. Installed it about 2-3 weeks ago, and have not had the chance to check it again until today, and the bilge is all but dry. There’s a tiny bit of water, but that is due to my one pickup being pulled off at an angle by the vinyl tubing – nothing some weight on the pickup won’t solve. Thanks for a great write-up!

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  6. Seth – this is an excellent writeup, thank you. I’m wondering – If I have just one bilge to dry, do you think a slightly larger diameter tubing would work better (1/4″ maybe)? Thank

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    1. 1/4” works better if your bilge always has water in it. But 1/4” works less well after your bilge is mostly dry. When the pickup is only sucking moisture from the sponge, 1/8” worked best in our tests.

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  7. Hey Seth, thanks for the quick reply, very helpful. I’m sitting on my boat on Lake Superior right now, thinking about how to make and install your system. Keep up the good work!

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  8. I can’t find any source for the 3/8 to 3/8 to 1/8 tee connectors needed for the manifold connections (I want to have 2 or possibly 3 sponges set up in different bilge areas of my 42′ foot boat). Any recommendations?

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