Automatic Bilge Switches
Revised by BoatUS editors in April 2012
Bilge pumps are commonly buried down in some dark hole, set on “auto,” and forgotten. BoatUS Insurance claim files are filled with instances of boats that sank from the misconception that automatic bilge pumps and switches are infallible. Most sinkings could have been prevented by the owner visiting the boat more regularly and checking a few key items.
Every time you visit your boat, you should check the water level in the bilge. You should know at a glance if it appears normal. Simply hitting the “manual” switch at the panel and listening for water discharge won't tell you if the pump has turned upside down, if the strainer is clogged, or if the automatic switch is still operable.
Of the different types of automatic switches available, all depend on rising water to activate electrical power to the pump. The most common type, and the most susceptible, is the float switch with an unprotected pivoting arm. Should debris jam the arm and prevent it from rising with the water level, the pump won't come on when it should and the boat could sink. Conversely, if debris blocks the arm from falling, the pump won't shut off until the battery is drained dead. Then it won't come on the next time it’s needed, regardless of the water level.
One remedy for a jammed pivot arm is to install a guard over the switch to protect it from the larger bits of debris in the bilge. However, pivot arms can also stick from an accumulation of smaller particles, oil, and grease that can pass through the guard. It's permissible, and perhaps even necessary, to mount the switch a little higher to keep the majority of debris below it and to keep the pump from kicking on prematurely.
Some automatic switches that rely on more sophisticated electronics are also prone to failure. Some, for example, rely on a microprocessor that senses water resistance against the impellor to turn the pump off. When there is no longer water resistance the bilge is theoretically dry. However these units have been known to fail and remain running until the battery is dead.
Remember the only guarantee that everything will work properly is to visit your boat regularly, inspect the various systems, take care of leaks immediately, and keep the bilges clean!
Information provided courtesy of Seaworthy, the BoatUS Marine Insurance Damage Avoidance Publication.
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