Every boat has bilges, where water collects, and these bilges have pumps for removing that water. A bilge pump is useful in two situations. Neither involves collision with an object that holes the hull, at which time a life raft will prove more useful than any pump. Bilge pumps are most often needed when a hose fails, as hoses inevitably will, or when water enters the boat while it is docked or anchored and unattended. A bilge pump failure under either circumstance is likely to sink the boat.
Rated
sizeBilge pumps are rated in gallons per minute and in amps of power draw. Gallon per minute ratings are wildly optimistic because they assume that the water is being diameter hose. A correctly sized bilge pump is the largest that will fit and that can be powered for a sufficiently long time, keeping in mind that the engine will not be available if the boat is unattended. The bilge pumps supplied by most boat builders are woefully inadequate.
How many? There is one manufacturer that makes most of the bilge pumps found in sailboats. Its pumps
How
many?There is one manufacturer that makes most of the bilge pumps found in many? sailboats. Its pumps are both economical and reliable, leaving little incentive to shop elsewhere. Once obtained, the properly sized bilge pump must be installed correctly and tested often. It is best practice to install bilge pumps in pairs, putting a small pump with a float switch at the lowest point and the larger pump with a separate float switch at a higher point where it will only activate on the rare occasions when the smaller pump is overwhelmed. Even if the boat has only one bilge, there should be at least two high capacity (3700 gallon per hour) bilge pumps. Because these pumps are prone to failure, boats over 35 feet should have three and boats over 45 feet should have four.
WiringBilge pumps that have float valves must be always on and therefore should not be wired through a panel switch. If they are switched, the switch should be always on. Adding an inline fuse is problematic; some standards require it, but it adds a likely point of failure. The wiring connections must be totally waterproof, and even so they must be located above the highest likely water level. Butt connectors and heat shrink tubing are not sufficient, let alone electrical tape, whether rolled or liquid. One waterproof Carlon boxes sold at home supply stores. The hole where the wires enter need not be plugged, if the box is firmly attached with that hole facing downward, because air pressure will prevent rising water from entering the box.
Hoses and check valves Hoses that connect the pump to a thru-hull should be as short as possible while including a loop that rises well above water level to
Float
switchPumps that are always on will of course require float switches. These must be firmly secured to prevent them from tipping and thus activating the pump in the absence of water, which will drain the batteries. The float switch is the weakest link, being susceptible to sticking, electrical failure, and clogging with debris and especially with hair.
and especially with hair. Hoses that connect the pump to a thru- Hoses hull should be as short as possible while and check including a loop that rises well above valves
HosesHoses that connect the pump to a thru- hull should be as short as possible while and including a loop that rises well above check water level to prevent backflow and is firmly secured at its highest point. A check valve can be used to keep water in the hose from draining back into the bilge when the pump turns off. The check valve will reduce the rate of flow, however, and it can stick in the closed position, making the bilge pump useless. Check valves should therefore be installed only on the hoses from the smaller, lower pumps and not on the main, higher pumps.
main, higher pumps. Pump maintenance Bilge pumps should be tested frequently and once a month is not too
Pump
maintenanceBilge pumps should be tested frequently and once a month is maintenance not too often. The best way to test them is by running lots of water into the bilge from a hose. Failing that, simply lift the floats on the float valves, keeping mind that rising water might not lift them simply because
you can and, besides, this test will not expose a stuck check valve unless there is water in the bilge. Carry a spare bilge pump with enough wire attached to reach a power point and with suitable clamps or connectors at the wire ends, and with enough hose attached to reach a porthole. A replacement for the smaller, lower pump and its check valve is often useful but not mandatory. A manual bilge pump is handy in many situations but cannot substitute for an electrical pump, nor can it serve as a backup. When water starts rising, you will have more important things to do, and you cannot expect to keep ahead of the rising water for very long with a manual pump. Manual bilge pump Diaphragm pump Most bilge pumps will not remove the last inch of water even with a check valve installed in the discharge hose. And no float switch will operate in an inch of water or less. A diaphragm pump can be installed to empty the bilge completely. It must be activated manually, by a switch, rather than by a float valve.