Shutting off water flowing through a hole in the hull
Many sailors still confuse sea-cocks with through-hull fittings, or through-hulls, as they are commonly called. A seacock is a special tap, or valve, that shuts off a flow of water; a through-hull is a metal or plastic lining for a hole in the hull. Every underwater through-hull hole on your boat should be fitted with a seacock capable of shutting off the flow of water that will result if a hose breaks or pulls away from the fitting.The seacock attaches to the inside tail of the through-hull fitting. Some seacocks have flanges that are bolted through the hull into the outside flange of the through-hull; others merely screw
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| Typical through-hull and seacock configuration. |
into the protruding tail of the through-hull.There are three common types of seacock used on small boats: the traditional tapered-plug seacock, the T-bar type with a swelling plug, and the ball-valve seacock. (Brass gate valves are also used frequently because they are cheap, but they have no place on a boat: they corrode quickly, and you can’t tell if they’re properly closed.)Bronze-bodied, tapered-plug seacocks are widely used and highly recommended. They need to be dismantled and greased at least once a year, but they have proven over time to be safe and reliable.T-bar seacocks also have bodies of bronze, but instead of a tapered bronze plug, they have a cylindrical neoprene plug. A threaded bar shortens the plug when it’s turned, forcing it to swell in the middle and make a very efficient seal. Certain chemicals can make the neoprene swell and prevent the seacock from opening or closing, so be careful if you’re directing discharge from the head or the galley.Ball-valve seacocks with bronze bodies have a hole running through the middle of a chrome-plated bronze or stainless steel ball turning in Teflon seals. They’re almost maintenance-free, requiring only a smear of petroleum jelly once a year or so. Those with bodies made of Marelon, a glass-reinforced nylon, are corrosion-proof and have gained wide acceptance, but they’re still not regarded as the equal of the bronze-bodied ones by conservative mariners.See also
Through-Hulls.
