Bilge Pump Basics

Due to the lack of maintenance they receive from the average boat owner, I often refer to bilge pumps as the Rodney Dangerfield of boat equipment, meaning "they just don't get no respect." It's a funny but also troubling statement, particularly because bilge pumps are often a boat owner's first and only line of defense against sinking. To prevent you from being that proverbial scared sailor with a bucket, here's a look at bilge pump basics &#; from what they do, to selection, installation, and maintenance.

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What They Are (And Aren't)

The primary job of most bilge pumps on most boats is to clear nuisance water from the bilges (packing gland drips, spray from an errant wave, etc.). The one that came with your boat may be up to that task, but a bilge pump should also be able to provide crucial extra time if your boat is taking on water, allowing you to find and deal with the source of a leak or, in extremis, to don life jackets and hopefully keep your boat afloat long enough for help to arrive. Most people upgrade to a larger bilge pump or add a backup bilge pump to give them time to deal with an emergency. Even that pump should not be confused with an emergency pump, which provides much greater dewatering capacity. If you plan on fishing the Canyons or sailing offshore, then you need a true "crash" pump, one that can move hundreds of gallons per minute.

This article will focus on the middle of these three options &#; the bilge pump meant to remove nuisance water but also to give you time to deal with an emergency. See the article "Bilge Pump Capacity: Do The Math" to figure out how much pumping capacity you need.

What Type Of Bilge Pump Do You Have?

The most common types of bilge pumps (and the primary focus of this article) are centrifugal and diaphragm electrical pumps. Centrifugal pumps move water by kinetic energy using a rotating, solid impeller, similar in design to a turbine. Water enters the pump, picks up speed as the impeller rotates, and is then forced out by its own momentum. Centrifugal pumps are submersible but not self-priming, meaning they must be sitting in water in order to pump it.

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Centrifugal pumps are relatively inexpensive and can move a lot of water. Other advantages include low maintenance, excellent reliability, and the ability to pass small amounts of debris without clogging. They can also run dry for extended periods without damage, although this does wear the bearing and will cause it to fail eventually. Disadvantages include their inability to self-prime and their loss of effectiveness the farther they have to push water vertically.

ean_p said:

Do you mean connect the pump discharge hose to a skin fitting within the boat but above the waterline lusty, or extend the hose through the companionway and over the side deck and gunnels then down to the sea's surface?

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Yes, for an emergency pump it's the latter. That way, once the pipe is full of water you no longer have to lift the water, just move it which greatly reduces effort. The pipe would need to be in the water to avoid the water running out. With the outlet on deck you're lifting 1kg up 5 feet for every litre of water. With the outlet in the water you're not lifting any weight at all.
Obviously a skin fitting would also work, but then you have another hole in your boat, and it would be one without anything connected most of the time so the cock would need locking closed just in case.
All a bit of a thread drift really as it doesn't help the OP it's just interesting, especially since Vyv mentioned potentially pumping for a few hours.

Yes, for an emergency pump it's the latter. That way, once the pipe is full of water you no longer have to lift the water, just move it which greatly reduces effort. The pipe would need to be in the water to avoid the water running out. With the outlet on deck you're lifting 1kg up 5 feet for every litre of water. With the outlet in the water you're not lifting any weight at all.Obviously a skin fitting would also work, but then you have another hole in your boat, and it would be one without anything connected most of the time so the cock would need locking closed just in case.All a bit of a thread drift really as it doesn't help the OP it's just interesting, especially since Vyv mentioned potentially pumping for a few hours.

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