It's unfortunate that most boatowners know more about their engines than they do about their bilge pumps. In fact, they'd probably be startled to discover the pumps are most likely inadequate.

When you buy a new boat, it already has a bilge pump installed, and you naturally assume that the manufacturer has done the homework and installed the right size. In many cases, however, that's a poor assumption to make.

Consider for a moment that the most common bilge pump installed in trailerable boats is the 500 gallon-per-hour (gph) variety: a compact plastic gadget in the bottom of the bilge. If you gave it any thought, you'd probably assume that, since the pump is capable of filling 10 50-gallon drums in one hour, it should certainly be more than enough to handle most emergencies . . . wrong!

If the hose on a one-and-a-half-inch through-hull (such as a water intake for a bait tank) slipped off a fitting just six inches below the waterline, you'd take on more than 1,900 gph. That means your 500 gph pump is losing ground at a rate of four gallons in for only one gallon out.

Change that to a two-inch though-hull fitting two feet below the water, and you're looking at nearly 4,000 gallons an hour. Move that two-inch through-hull fitting to three feet below the waterline, and the water flow increases to 5,000 gallons each hour. Still think your 500 gph bilge pump is sufficient? You might as well be bailing with a Dixie cup. While the U.S. Coast Guard and federal equipment requirements decree that you must have a certain number of life jackets, fire extinguishers, flares and even a horn on board your boat, the regulations are surprisingly silent about bilge pumps. You aren't even required to have a bucket!

If you want to pass the voluntary Coast Guard Auxiliary Courtesy Motorboat Examination to earn your CME decal, you need to have what they euphemistically call a "dewatering device," meaning a bucket or scoop ' and they say it must be "effective." It's been said that the best bilge pump is a scared boater with a bucket, but even at a minimal 1,900 gph intake from a broken through-hull, you'd need to move 31 gallons a minute just to break even. And how long can you keep up that pace?

This brings us to the second part of the bilge pump problem ' who can you believe when it comes to the pump's flow rate? Many manufacturers rate their pumps at what is called "zero head," which means the pump is moving water sideways at the same level. In reality, your pump is in the bilge below the waterline, and the outlet through the hull side may be several feet above the pump.

Sadly, bilge pumps are not nearly as effective at lifting water as they are at moving it sideways. A pump that moves 1,000 gph at zero head may only be able to pump 400 gph at a three-foot head, and even less at a six-foot head. In addition, the American Boat & Yacht Council (ABYC) recommendations for testing bilge pumps are not only at zero head, but with what is called "open flow," which means there is no hose connected to the outlet side of the pump. As soon as you add the hose to route the water from the bilge pump up to the hull outlet, the flow is reduced even further from friction.

Compounding the problem, the flexible corrugated hose that most manufacturers use for simplicity of installation cuts down the flow even more than a smooth hose. Use a corrugated hose, and your bilge pump is 20 percent less effective than before. Add a loop to prevent backflow and it gets even worse
Let's revisit the example of a bilge pump rated by the manufacturer, using ABYC standards, at 500 gph. When you make that pump lift the bilge water just three feet before dumping overboard, that pump is down to 300 gph. Since you're using a corrugated hose, take off another 60 gallons and you're at 240 gph, or less than half the pump's "rated" capacity. If you still think that you can cope with even a small leak, think again, because you're literally going to be sunk.

Now let's talk about how to properly equip your boat. First of all, there should be at least one bilge pump in each separate compartment of your hull. In many cases, builders will seal off the engine compartment from the cabin, so that means you will need a pump for each area. At a minimum, each pump must be capable of handling the intake from any through-hull in that compartment. For example, if your engine compartment has a 1 1/2-inch through-hull at a depth of six inches, the pump should be capable of moving at least 1,900 gph.

Now that you've figured out a reasonable capacity for your pumps, you need to install them properly. They should be solidly mounted as low in the bilge as possible, and you want to make sure that your bilge pump has a strainer to keep debris from clogging the impeller. Check also to see if the strainer can be easily cleaned, and make that a part of your routine maintenance.

The next step is to make sure the bilge pump will operate when you need it, and that means you need an automatic pump switch. These switches activate your pump when the water level reaches a certain point, even if you're not on board your boat at that time.

There are any number of switches available, ranging from the least expensive hinged floats to more expensive electronic versions. Float switches, if not protected from debris, can be jammed in both the on or the off positions, leading either to no pumping action or a burned-out motor from extended dry pumping.

There are also pressure-activated switches that sense the change in air pressure as the bilge water rises to trigger the pump, but these are susceptible to leaks and need to be tested regularly. Probably the most reliable automatic pump switch is the magnetic version, which seals a magnet into a floating rubber element. As the float rises in the protected housing, it activates the pump and, with no arms to jam, is unaffected by debris in the water.

Remember that an automatic switch on your bilge pump isn't just for those times when you're away from your boat. Leave your pump in the automatic position when using the boat, because you're likely to be too busy to bother checking the bilge on a regular basis.

For peace of mind when you're away from your boat, there are two things you can do. First, wire a simple electronic counter into the bilge pump circuit. These are available inexpensively at electronics stores such as Radio Shack, and they literally count the number of times your bilge pump cycles on. If you've been away from the boat for a week and the counter shows three cycles, then you have nothing to be concerned about other than some stray rainwater or a very slow drip. But if the counter shows 247 cycles, it's time for you to start worrying, because you've obviously got a steady leak.

The second thing is to install a bilge alarm system. Any serious leak may be too much for the normal bilge pump to handle, and the pump will quickly drain the batteries, resulting in a sunken boat. Besides, in today's marina, who pays any attention when a neighbor's bilge pump starts running? What you need is a way to alert the harbor patrol to the problem, so mount a second automatic switch at a point about six inches above the primary automatic bilge pump switch. Rather than attaching it to a bilge pump, wire it to the boat horn. This allows your bilge pump to handle normal leakage, but if the water rises to a critical level and reaches the secondary automatic switch, the horn will blast. It's certainly a good idea to notify your marina about the alarm, but even if you don't, the noise will bring someone to investigate further and save the boat before it sinks.

Properly wiring your bilge pump is also important, particularly since many manufacturers provide only a few inches of wire pigtail, which means that your wire connections are likely to be in the bilge. If possible, seal your bilge pump connections with a "liquid tape" compound from a marine hardware store. This will keep water from corroding the wiring or shorting it out at a time when you need it most.

Last, pay some attention to your bilge pump. It's in an unfriendly environment, submerged in water and bilge muck, overheated by the engine, and often allowed to run dry. Most bilge pumps are designed to be taken apart easily, so clean the debris out of the strainer on a regular basis, check the impeller for broken vanes, and make sure the wiring is protected from the effects of the water.

Considering the price of bilge pumps, they're one of the best hull insurance policies you can buy for your boat.

September 2001