BoatU.S. - December 2011

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KEEP IT HIGH WHEN FEELING THE DRAIN I’M NEW TO SAILING AND A NEW OWNER of a 1983 Hunter 22 that has three thru-hulls — one for the knot-meter transducer, one for the galley sink, one aft for the cockpit drain. It also has deck drains and an anchor-locker drain above the waterline. I want to install a bilge pump but don’t know where to route the discharge. Should I tee into the galley drain that’s close to the bilge pump well, or to one of the above-waterline drains? If I need a new thru-hull, where should it be? Greg Rogers

Dallas, TX

DON CASEY: Bilge-pump discharge openings are ALWAYS located above the waterline, and need to be far enough above so that they can never be submerged, either by heeling, or by the stern wave when the boat is moving fast. A discharge line can pass water into the boat just as easily as it passes it out. If, for example, you tee into the sink drain above the waterline, and that connection dips below the waterline when the boat’s heeled, water will flow straight into the bilge, flooding the boat. This is equally true of a dedicated thru-hull discharge located just a short distance above the waterline. Even if you route the discharge

hose in a high loop before it connects to the outlet, should the pump run while the outlet is submerged, when the pump stops, the full line will set up a siphon and water will again flood into the boat.

Adding a check valve into the discharge line is a bad idea. It not only reduces the capacity of the pump, but the valve can catch debris, blocking the discharge. It will also soon gather enough debris to prevent the valve from sealing, defeating the purpose. The best place for a bilge-pump discharge is high on the transom, just below the deck joint. A thru-hull located here is unlikely to become submerged in normal sailing. If this location is impractical due to the location of the pump, or the design of the boat, then a just-below-the-rail location on either side of the hull can work, assuming that you do not regularly bury the rail when sailing.