Choosing the Right Bilge Pump for Your Boat

When the bilge pump is the only thing that can prevent your boat from sinking, it’s best to have one capable of handling the burden of pumping out as many gallons of water out as fast as it can.

Boat bilge pump guide

All boats collect some nuisance water within the hull. This water typically comes from waves, spray, rain and leaking thru-hull fittings, but can also come from virtually anything from melting snow to the water people bring onboard with them. Even small amounts of water in the bilge can destabilize a boat. Bilge water can also spread spilt oil and fuel around the hull, which can damage plastic and rubber components, and lead to blistering in fiberglass hulls. Enough bilge water within a hull can sink an entire boat. 

Boat bilge pump system failure

How Many Bilge Pumps?

All powerboats have a standard bilge pump to deal with the nuisance water that collects within the hull. These are submersible electrical pumps found in the lowest part of the hull, typically the stern.

Boat bilge pump system

Standard pumps are usually small and only capable of removing low volumes of nuisance water. They’re often incapable of dealing with large quantities of water from emergency situations caused by a hull breach or the total failure of a through-hull fitting or seacock. Because of a standard bilge pump’s limited capabilities, installing a second, larger bilge pump capable of expelling more water in emergency situations is highly recommended. On boats with multiple hull compartments, you’ll need a standard bilge pump for each compartment, plus an emergency bilge.

What Size Bilge Pump?

When it comes to bilge pumps, bigger is always better, provided a larger capacity bilge pump can fit in the space where it needs to be installed.

Boat bilge pump system high capacity

Bilge pumps are rated by the number of gallons per hour they can pump. However, due to various factors, the actual performance of a pump is always lower than its given pumping capacity. For example, a pump rated at 200 GPH (gallons per hour) might only be capable of pumping 120 GPH. 

Standard Bilge Pumps

Most standard bilge pumps aren’t capable of pumping much water, so consider upgrading to higher capacity pumps, even if your boat is new.

Choosing boat bilge pumps guide

If the standard electrical bilge pump in your boat’s hull isn't capable of preventing your boat from sinking, it should at least be able to pump out enough water to buy you the time needed to find and plug a leak in your hull. 

Emergency Bilge Pumps

An emergency bilge pump needs to be capable of pumping hundreds of gallons per minute to save your boat. High-capacity emergency bilge pumps might be expensive, but will seldom (if ever) be used and shouldn’t wear out. Ultimately if a more expensive emergency pump ends up saving your boat from sinking, it’s worth the investment. Emergency bilge pumps can also be mounted higher up in the boat so they aren’t submerged in nuisance water, and can therefore last longer than a standard pump.

Bilge Pump Accessibility

When buying a new bilge pump, consider how accessible it’ll be. Not only will the pump have to fit into a specific space, but it needs to be easily accessible for routine inspection, maintenance and repairs. This consideration applies more for standard bilge pumps that have to be mounted at the very bottom of the hull than emergency pumps, which have more flexibility on where they can be installed.

Diaphragm Bilge Pumps vs. Centrifugal Bilge Pumps

Diaphragm Bilge Pumps

A diaphragm bilge pump uses the movement of a rubber or plastic diaphragm to draw water in through an intake valve, and then out through an output valve to the discharge pipe.

Diaphragm bilge pumpPros: Extremely efficient at pumping water upward against gravitational forces. Self-priming, and can be mounted above water.

Cons: Easily clogged by debris and thus requires adequate screens or filters, which require regular inspection and cleaning. Can’t pump the same volume of water as a same-sized centrifugal pump.

Diaphragm pumps are more suitable as emergency bilge pumps.

Centrifugal Bilge Pumps

A centrifugal bilge pump uses the movement of a spinning impeller to suck water into the pump housing and out through the discharge pipe.

Centrifugal boat bilge pumpPros: Extremely efficient at pumping large volumes of water. Less susceptible to debris within the water being pumped. Very reliable and low maintenance.

Cons: Can’t pump water as high as a same-sized diaphragm pump. Not self-priming, so must be mounted below water level.

Centrifugal pumps are more suitable as standard bilge pumps.

Automatic Bilge Pumps

These bilge pumps have built-in float switches that turn the pump on when bilge water is detected. If you can’t find an automatic pump suitable for your boat, buy a separate float switch and pair it with a non-automatic pump.

Rule-A-Matic bilge float switch

Bilge pump with float switch

If you do have an automatic bilge system, you should still check your bilge regularly for signs of any potential problems. Your boat’s bilge pump might be able to cope with an old thru-hull fitting that is starting to leak, but once the fitting fails completely, the pump will become overwhelmed. A bilge water alarm that warns you when the level of the bilge water rises is a sensible addition to any bilge system. 

Bilge water alarm and float switch


Bilge pump water alarm system

Electric Bilge Pumps vs. Manual Bilge Pumps

An electrically powered bilge pump sounds better as an option to buy than a manually operated bilge pump, but isn’t necessarily the best choice. 

Boat bilge pump system

In an emergency flooding situation, your boat’s electrical system can short out and if that happens, an electric bilge pump will be rendered useless. Instead, a bilge system that includes both an electric and a manual bilge pump for emergency use is recommended. The most important thing to look for with a manual pump is ease of use. Pumping hundreds of gallons by hand will soon become exhausting work, so a manual pump with a high pumping capacity that can be easily installed is recommended. 

Additional Considerations

Replacing a bilge pump is much easier if you choose a new pump that uses the same size hoses and pipes as the old one. Otherwise, you’ll need to replace the various hoses, pipes and thru-hull fittings for a higher-capacity pump.

Boat bilge pump guide

Also, add a non-return valve or check valve to the discharge pipe to prevent any water in the pipe from flowing back into the bilge when the pump is turned off.  It prevents any water from entering the boat if the discharge pipe’s thru-hull fitting gets submerged.

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