Virtually all boats end up with unwanted water in the bilge, which must be removed by a bilge pump. Water gets in from a propeller shaft packing gland, a leaky portlight, leaky seams in a wood boat, melting ice from the icebox and a multitude of other sources.
Getting nuisamce water out of your boat is the primary function of a bilge pump. Leaving large amounts of water in the bilge can create unpleasant odors and have several undesirable effects on your boat, including destabilizing it, spreading fuel throughout the bilge and may prompt the development of blisters in fiberglass hulls and, in a worst case scenario, sink your boat.
In some cases, the leak may be catastrophic from a collision or a wave taken on board in a storm. These situations call for high pumping capacity and for the most part, the largest pumps will only buy you a little time to make repairs, limp back to shore or make preparations to abandon ship. For emergency situations like this, it is advisable to have multiple electric pumps and at least one high-capacity manual diaphragm pump.
Therefore, we’d like to reinforce the following words of wisdom regarding bilge pumps so you’re not disappointed in the future:
- Virtually no boat has a bilge pump system that is large enough to keep up with a leak caused by hull damage. Bilge pumps are designed for small quantities of water and are not damage control pumps like the ones Coast Guard helicopters drop. The American Boat and Yacht Council standards for electric bilge pumps state that they are “intended for control of spray, rainwater and normal accumulation of water due to seepage and spillage.”
- Never leave a boat with a known leak alone with an automatic bilge pump in the hope that it will keep your boat afloat. We receive an occasional angry letter from a customer who claims that his boat sank because the pump we sold them did not keep their boat afloat. Of course, there are lots of reasons that a pump could fail to remove water from a boat, and you should never trust a pump to keep up with a leak. If your boat has a leak, haul it out and get it fixed.
- Bilge pumps are only as good as the system its attached to. This includes the batteries, wiring and plumbing. An electric bilge pump can last only as long as the batteries and poor and/or corroded wiring or blockages in the plumbing will also have negative affect on the pump’s performance.
With that out of the way, let's jump into finding the right size and type of pump for your boat
- Sizing Your Bilge Pump
- Replacing an Existing Pump
- Types of Bilge Pumps
- Panels and Switches
- Bilge Pump Installation Tips
Sizing Your Bilge Pump
Electric bilge pumps are rated by their capacity, which is measured in gallons per hour, or gallons per minute, under open flow conditions with no restrictions to the discharge. The rule of thumb is to get the largest model that is practical for the boat. Your selection will depend on size constraints and power limitations, but choose a 1,000gph model or larger, if possible. Submersible pumps generally have great open flow capacity, which rapidly decreases depending on how high the water is lifted.
Remember that small boats need good-sized pumps because:
- Hull volume is smaller, so a small boat will sink more rapidly than a large boat
- Less freeboard means small boats get swamped more easily
- The bilge is smaller, so water will flood the engine and electrical system sooner
Replacing an Existing Pump
Match existing hose sizes and wire capacity, unless you want to upgrade the wiring and the thru-hull size too. Buy the largest capacity pump that uses the same hose diameters. For a few dollars more you can increase pump capacity significantly and still keep the same hose diameter. For a new installation, use the largest practical pump size.
Types of Bilge Pumps
Mechanical
Mechanical bilge pumps, like this 2000 GPH pump are operated using a panel, a float switch or both. Mechanical pumps generally have the largest range of capacities from 360 GPH to upwards of 4000 GPH and are great for mooring and the occasional user. Make sure to regularly check your float switch to make sure it's operating properly. A faulty float switch will not activate your pump and potentially lead to excess water in the bilge.
Automatic
Automatic bilge pumps like the Rule-Mate line feature an internal water-sensing switch which eliminates the need for an external float switch making your installation take up less space than a mechanical pump. This makes automatic pumps easy to install and great for tight spaces and small bilges. Automatic pumps also avoid any “nuisance tripping” as the boat bumps and jolts through the water which can accidentally trip the float switch on a mechanical pump. Capacities range from 500 to 2000 GPH making them a great choice for a variety of boats.
Computerized
Computerized bilge pumps, like this 500 GPH pump, turn on for half a second every 2.5 minutes to check for water and leave the least amount of water in the bilge at all times. Computerized pumps are the smallest profile automatic pumps and are popular in trailer boat applications as they are great for shallow bilges. These pumps are also very efficient, only drawing approximately .25A per day in cycling mode.
Panels and Switches
Mechanical bilge pumps are activated by an external float switch, a panel at the helm or both. Three-position switches are a great option as they allow you to activate the pump manually, set the pump to auto to be activated by the float switch or turn the pump off completely when the boat is out of the water. When installing an external float switch, mount the switch at approximately the same level as the base of the pump to help ensure the pump won't run dry.
Bilge Pump Installation Tips
- Keep discharge hoses as short as possible. Long hoses have more resistance, which reduces pump performance
- Run discharge hoses continuously upward. This helps prevent air locking of the pump.
- Use smooth bore hose. It is common to install corrugated hose for price reasons, but the ribbed inside reduces flow and decreases the pump's performance.
- Use a vented loop if the thru-hull can be submerged, especially on sailboats where heel might immerse the fitting that is well above the waterline when the vessel floats on an even keel.
- Follow the manufacturer’s recommendations for wire sizes to prevent voltage drop, especially on pumps that draw 10, 15 amps or more. Use the wire charts in the Electrical section of this website and size wiring for a three percent voltage drop.
- Use waterproof butt connectors for any wiring connections in the bilge area. These wires are notorious for getting water inside the insulation and turning into green mush.