Boating Writer’s International Award winning article
The more you know about bilge pumps, the less chance you’ll end up being the proverbial scared sailor with a bucket.
by Frank Lanier
When a boat owner finally works up the nerve to reach down into the questionable waters of the bilge, it’s usually to determine why a pump failed, rather than how to keep it running. Next to hull integrity, the bilge pump is a vessel’s first and often only line of defense against sinking, yet many boaters have developed a frighteningly cavalier attitude toward its maintenance and operation. We carry lifejackets and flares, yet we routinely overlook precautions that might make those things necessary—like making sure we have the right kind of pumps in the bilge and enough pumping capacity. Knowing how bilge pumps work, how many you should have and how to spot installation problems is a good place to start, if you want to get the most from this vital piece of safety equipment.
Know Your Type
Bilge pumps perform two functions: ridding the boat of normal water accumulations (dripping stuffing boxes, for instance) and helping to control flooding in emergencies. The most common types are centrifugal and diaphragm electrical pumps. The centrifugal pump moves water by kinetic energy—water enters the pump, picks up speed as the impeller rotates, and is then forced out by its own momentum. It’s a relatively inexpensive pump that can move a lot of water, and it’s designed to operate when completely submerged. Most centrifugal pumps can pass small amounts of debris (like paint chips or lost washers), but the farther they have to push water vertically, the less effective they become.
The diaphragm pump acts like a little wet-vac to suck out bilge water. The diaphragm pulls water through an intake valve and then pushes it through an output valve. This type of pump is better able to push water uphill. But its check valves are prone to clogging and failure, and it generally can’t move as much water as a centrifugal pump. Because it’s not waterproof, you must mount it out of the bilge (which also makes it easier to maintain). Diaphragm pumps are bigger than centrifugal units, so they need more space and more power to operate.
A third electrical type is a flexible-impeller pump, which combines the priming features of a diaphragm pump with the capacity of a centrifugal type. It uses a flexible impeller to draw water in, prime the pump and keep it moving toward the discharge outlet (engine-water pumps are a good example of this type). Flexible-impeller pumps can be mounted at any angle and are efficient at low or high speeds, which make them popular for pressurized freshwater systems. But these too are not submersible and must be mounted well above the bilge. Another downside: They don’t pass debris well and they can burn up in a couple of minutes if run dry—all characteristics that limit their usefulness as bilge pumps.
If you don’t want to count entirely on your electrical system to power your pumps—and you probably shouldn’t—you’ll need manual pumps too. They’re useful as backups, but keep in mind that they run only on elbow grease; even a fit crewmember will have a hard time keeping up with one after awhile, assuming you have a spare crewman for the job. The two most common manual pumps are diaphragm and piston types. Manual diaphragm pumps work on the same principle as the electrical versions; they can be fixed or portable, are self-priming (that is, they develop suction and prime themselves when dry) and can be single or double action, using single or multiple diaphragms. Some larger ones are rated at 50 gallons per hour (gph). Piston pumps work just as their name implies: You pull on a handle that draws a piston up a tube, sucking water along with it and flushing it out of a hose. These pumps are portable and can move about a gallon of fluid with every four strokes.
Finally, you may want to consider an engine-driven emergency or safety pump. Ericson, for instance, makes a safety pump that permanently attaches to the propeller shaft and pumps as the engine is running and in gear. Ericson’s smallest pump, for shafts up to 2 inches in diameter, can pump 4,800 gph at 800 rpm and up to 25,500 gph at 1800 rpm. The company’s bigger pumps, for 2- to 6.3-inch shafts, are rated at 54,000 gph at 300 rpm and up to 75,600 gph at 500 rpm. They aren’t cheap; the smallest model is about $1,600, while the larger pump goes for about $3,300. Overkill? Perhaps, but consider this: A 2-inch hole in the hull 4 inches below the waterline can let in more than 9,420 gallons per hour. If the hole is just 2 inches lower, it sucks in 60,000 gallons per hour. A 6-inch hole 4 inches below the waterline increases the flow to 84,840 gph, an amount even the best system won’t be able to keep up with. A cheaper option might be installing a suction takeoff from the main engine pumps. Just remember that running the engine pump dry will damage the impeller, and that the intake connection should be in front of the sea strainer (so you don’t suck bilge debris into the engine). This is a proven and accepted pumping method, but know what you’re doing before you do it—otherwise you can seriously damage your engine.
Pump Up the Volume
Now that you know how different pumps work, you need to determine how many your boat should have. The first thing to understand is that just because the writing on the bilge pump box says it can pump 500 gph, that doesn’t mean it can. Several factors affect pumping capacity, and while a manufacturer might get a pump up to 500 gph in the ideal horizontal conditions of a lab, the real world is another matter. On most boats, water has to be pumped up before it can be pumped out—and that’s a critical factor. The distance of vertical travel, called static head by the guys in lab coats, can decrease a pump’s rated performance by as much as 75 percent. Just 2 feet of static head will cut the output of a small centrifugal pump by half, and 15 or 20 feet might neutralize the pump entirely, depending on its size. Sailboats make things even more complicated; though a pump in the keel sump may have to lift water only 5 feet when the boat is level, heeling can increase that distance by 3 feet or more. Other factors degrading performance include bends and restrictions in the discharge line, as well as hose size and interior surface (small hoses with ribbed insides are the worst).
So how much pumping capacity should your boat have? That’s a good question—and one with no clear or easy answer, mainly because boats are so different. Any compartment that’s essentially watertight—where water can’t escape into another area—should have its own pump or two. The American Boat and Yacht Council has not set requirements concerning bilge pump capacity, though the American Bureau of Shipping recommends one 24 gallons per minute pump (that’s about 1,440 gph) and one 12-gpm pump for boats under 65 feet. The Lloyds’ standards relate to vessel length and volume, recommending a 50-gpm pump for a boat about 50 feet.
To me, it’s a simple case of bigger is better—within reason, of course. Based on size alone, I’d recommend a minimum 5,500 gph electrical pumping capacity for a 40-foot vessel—divided among a 1,500-gph primary pump and two 2,000-gph backup pumps.
Ready, Willing and Able
Once you’ve determined the types of pumps you want and how many, the next step is making sure they’re installed and maintained properly. Maintenance begins with the bilge itself; no pump can overcome a bilge choked with trash, so a good old-fashioned cleaning is the first order of business. Periodic bilge cleaning is a fact of life with older vessels, but even the bilge of a brand-new boat can be littered with wood shavings, bits of fiberglass, globs of adhesives and other construction trash that can plug up a pump. Oil in the bilge is just as bad; it combines with dirt to form a nice gooey sludge that can clog pumps and prevent float switches from operating properly.
Your larger pumps and their associated float switches should be mounted higher than the primary pump. This lets the smallest pump take care of normal seepage (with less battery drain) and leaves the larger ones to kick in only when needed. (Regarding battery drain, allow me just a moment on the soapbox: No matter how much time and money you invest in an electric bilge pump system, it will never be better than the batteries that power it. Ditch those car batteries and get yourself some sure-nuff honest-to-goodness marine batteries.)
Make sure all the pumps, float switches and strainers are easily accessible—something essential for routine maintenance and emergency repairs. Remove, disassemble and inspect pumps at least twice a year for broken or worn parts. This is just good preventive maintenance, but it also gets you familiar with disassembling and reassembling before the feces hit the rotary oscillator. Check that all pumps are firmly mounted, paying particular attention to the mounts themselves, which may develop hairline cracks. List each pump by type, location and size for future reference—don’t forget shower and galley sumps—and make sure you have sufficient spare parts onboard for each. Check that each of the intake strainers is securely fastened in place, and while you’re at it clear them of any gunk that may have accumulated since the last check.
Float switches must be securely mounted and installed clear of wires, hoses and other obstructions that can impede operation of the floating-arm or flapper switch. Orient the switch fore and aft, with the flapper pointed toward the stern. This is especially important on powerboats—during jackrabbit takeoffs, surging bilgewater can damage the flapper mechanism. Installing them close to a bulkhead or frame also helps protect the switch from a torrent of water. Enclosed switches eliminate this worry, but they’re difficult to inspect and test. I like having the float in plain view, where I can keep an eye on it.
Advances in switch technology range from microchips and magnetic relays to air-pressure sensors and even water-conductivity sensors. Rule Industries, considered by many to be a leader in the bilge pump business, now has switches that activate themselves at a low level in timed intervals to sense for water. If the pump detects water, it kicks itself into pumping mode. Some switches even have sensors that let them distinguish between water and other fluids, reducing the chance of illegal discharges. Regardless of the type you choose, make sure each pump has a manual switch as well; none of the automatic systems is failsafe.
Inspect all hoses (ensuring that each is double clamped with stainless steel clamps), as well as the discharge through-hull fitting, which can develop stress cracks from supporting the weight of the hose. Securing the discharge hose to keep it from bouncing around will go a long way toward stopping this problem. The discharge through-hull itself should be well above the waterline to prevent water from siphoning back into the bilge. Boatbuilders often install them low to eliminate hull-staining backsplash, but that’s a dangerous concession to tidiness; a change in waterline (by adding many pounds of extra gear, for example) could easily put the through-hull at or below water level.
Riser loops add some margin of safety, but be sure they reach at least 18 inches above the static waterline.
Most bilge pump failures can be traced to corroded electrical connectors, either at the float switch or at the pump itself, so inspect all wiring and connections to make sure they’re properly sealed and installed well above water levels. If you find connections made with electrical tape and household twist-on connectors, replace them with proper marine, heat-shrink connectors. ABYC standards recommend providing circuit protection for each pump. You can do this by powering them through the main breaker or fuse panel, but then you’ll have the potential problem of someone inadvertently killing power to the pumps by throwing the main breaker. To prevent this, some advocate wiring them through a dedicated fuse to the “all” or hot terminal of the battery switch (the one that’s always energized), or even directly to the battery itself. The switch is the better option, as it’s generally poor practice to wire equipment directly to the battery. The battery switch option also ensures the pump can draw power from both batteries, rather than limiting them to one. I took the dedicated-line-and-fuse approach one step further on my last boat; for all the pumps onboard, I installed a small dedicated breaker panel, which I then wired directly to the battery switch, bypassing the main circuit breaker. It keeps all the pump fuses and breakers together and easily accessible. I also fashioned a small, Plexiglas cover and stenciled do not turn off on it.
Many make light of bilge pumps by quoting that old nautical adage: The best bilge pump is an activated bucket. That’s funny, and perhaps true up to a point. But scared folks get tired too—and often long before whatever’s letting all that water in is fixed. So to keep passengers from having to choose between grabbing their lifejackets or joining the bucket brigade, be serious about your bilge pumps. They may help save your boat—or even your life—someday.