Skip to main content

Keep Your Bilges Happy

It’s not very exciting, but your bilge needs love too.

When was the last time you visited your bilge? Probably not recently: Most of us ignore our bilges, even though they’re always right underfoot, but bilge TLC should be a regular maintenance item. No, it’s not a sexy job, not as exciting as tuning your turbodiesel, nor as satisfying as laying on a perfect coat of varnish, but there’s gear down there—pumps, plumbing, seacocks, wiring—whose failure can cause big problems—such as sinking. And even if all the under-sole systems are fine, a dirty, smelly bilge is a sign of poor boatkeeping.

Cleanliness Is Next to Godliness

Step one is keep the bilge clean, often easier said than done since there are sections of most bilges as unreachable as the dark side of the moon. But there’s good access in most machinery spaces, since they’re set up for maintenance, and, in a properly designed boat, cabin-sole hatches reveal pumps and other equipment outside the engine room. So apply biodegradable soap and water to the places you can reach, especially machinery spaces where oil and fuel leaks are possible. You won’t see drips if the bilge is dirty, but they’ll be obvious when it’s clean. (See “Why You Need an Engine Pan,” on page 88.)

Clean out the limber holes, the openings in frames, stringers, and non-watertight bulkheads that let water flow into the sump where the pump lives. Clogged limber holes turn bilge sections into stagnant swamps. Wooden-boat builders used to string a flat brass chain through the limber holes from stem to stern; shaking the chain would dislodge junk and let water flow. You don’t see limber-hole chains very often today, so use a piece of stiff wire (another use for a straightened coat hanger) or another instrument to clean them out. 

Frames and stringers are usually hat-section fiberglass laid over a core of wood or foam; drilling limber holes without sealing their edges lets in water that over time will cause delamination or core deterioration or, usually, both. If you find unsealed limber holes, call in an expert—a surveyor or your yard manager—to check it out. Don’t ignore it.

“A dirty, smelly bilge is a sign of poor boat-keeping.”


Keep Your Pumps Pumping

Test each of your bilge pumps in both automatic and manual modes, and then clean the pump and its remote switch. Every bilge pump should have protection against ingesting foreign matter, either a screen built into the body of a submersible pump or a strainer (a “strum box”) on the intake of a remote pump. Whatever its design, keep the screen free of foreign matter. Keep debris away from float switches, too. Otherwise, as sure as death and taxes, something will either jam one open, so the pump runs constantly and eventually burns out, or closed, so the pump never runs at all. There are also pneumatic switches activated by water pressure, more often matched with remote-mounted diaphragm pumps; in my experience, both are reliable and nearly maintenance-free, as long as you keep gunk away from them.

Some skippers protect their float switches with homemade wire-screen boxes, which you have to clean regularly, and some come factory-encased in a plastic basket, which you also have to keep clean. Save yourself maintenance headaches when it’s time to replace a bilge pump by selecting one with a built-in switch. For example, Rule-Mate pumps ( incorporate water-sensing technology, not a float switch, that turns the pump on when the water passes a certain level, and off when it’s gone—like a float switch, only better, according to the company. Unlike automatic bilge pumps that constantly check for water, the Rule-Mates operate only when there’s water to be pumped.

Or maybe it’s time to replace the float switches with newer technology, something like Attwood’s S3 series ( Using solid-state wizardry to sense water levels and start the pump, the S3 can sense when the bilgewater is contaminated with oil, fuel, or chemicals, and not pump them overboard. Water Witch ( is another highly rated builder of electronic switches. The company claims they’re used by both the U.S. and Canadian Coast Guards. There are also automatic pumps that don’t have switches, but cycle constantly, 24/7. If they sense water (through back-pressure against the impeller), they keep pumping until it’s gone; otherwise, they shut off after a second or two and do it again in a couple of minutes. Both automatic pumps and solid-state switches use a tiny bit of electricity, as opposed to a float switch that uses none.

Check the Extras, Too

Every automatic bilge pump should have an indicator light on its control panel showing when the pump’s running—no help when the boat’s unattended, but a good warning of trouble when you’re underway. Most boats should also carry a bilge-level alarm, situated to sound before rising water reaches wiring or other vulnerable components. Test both systems, and the manual pump switches, too. The visual bilge-pump indicator is required by ABYC standards for all boats, the bilge-level alarm is required for all boats with enclosed accommodations. I’d install a bilge-level alarm on any boat with an engine compartment, i.e. an inboard or sterndrive, whether it had a cabin or not.

Install a counter on each pump to record how often it operates. Keep a log of typical cycles over a given period of time—maybe Monday through Friday when you’re at work and the boat’s in the marina. If you spot an uptick in cycles you’ll know it’s time to check things out. (Since automatic pumps cycle every couple of minutes, a counter won’t help much; a timer recording total pump operation would be more useful.) 

Don’t Stop at the Pumps

While you’re in the bilge, inspect everything. Locate and operate every seacock or ball valve, check every hose and its connections at both ends. If a submersible bilge pump discharges through a vented loop (required if the discharge is near the waterline), make sure the vent is clear to prevent water from siphoning back in; ensure there’s a seacock on the through-hull. Remove, check, and replace a hose clamp or two to ensure they’re marine-grade, 100-percent stainless steel. Be alert for boatyard- or owner-installed accessories that might not be up to industry standards, which for most boats means ABYC standards. (You can access the standards for a short trial period at

Nitpicking may save your boat: Based on claims filed with BoatUS Marine Insurance ( since 2006, more than one in four boats that sank did so because “some small part gives up the fight … due to wear, tear, and corrosion,” according to a recent BoatUS newsletter. (69 percent of sinkings happened at the dock or mooring rather than underway; 39 percent of them were caused by equipment failure. Crunch the numbers and you get 26.9 percent of the total.) These are sinkings due to causes that regular inspection and maintenance most likely would have prevented. Don’t be the one skipper in four who let his or her boat sink due to inattention. And start with the bilge.


Why You Need an Engine Pan

Nothing fouls a bilge faster than engine drippings: Even a minuscule amount of unnoticed oil or fuel will surf into the farthest reaches of the engine room where it’s a pain to clean up. If you don’t remove all of it, some will inevitably find its way into the bilge pump and overboard. (Nothing makes you unpopular around the marina faster than an oil slick.) Save yourself the scorn of your slip neighbors by installing drip pans to catch any errant petroleum products. Most top-quality boats come with them as standard equipment, but adding one won’t cost much, and is well worth the expense.

Even if your mechanicals are completely drip-free, eventually something will leak out, even if only during maintenance or fluid changes. With a drip pan to catch it, clean-up involves the swipe of a rag or paper towel. And if you keep the pan clean (which we know you will), you’ll spot any unexpected drips immediately when you do your engine checks. You’ll want a pan installed anywhere lube oil, fuel, hydraulic oil—in short, any fluid—can leak out. That means installing pans not only under each engine and generator, but under the transmissions, too.

Although any fluid-tight receptacle that fits properly under the engine can serve as a drip pan, most are custom-made, and metal—stainless or copper—is easiest to keep clean and looks coolest, too. Unless you’re an expert welder, it’s a job for the boatyard, but one that’s well worth doing. You don’t want your marina mates calling you “Old Oil Slick.”

This article originally appeared in the September 2014 issue of Power & Motoryacht magazine.