One Good Turn Page 2

One Good Turn — Maintenance April 2001
One Good Turn
Part 2: Through-hull fittings continued

By George L. Petrie
 More of this Feature
• Part 1: Through-Hull Fittings
• Part 2: Through-Hull Fittings continued
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Inboard of each through-hull connection, seacocks are your best defense against catastrophe in the event of a serious leak or rupture in your vessel's piping systems. The seacock's sole purpose is to let you close and tighten a through-hull connection.

Check that a seacock has been installed on each fitting that penetrates the hull below its load waterline, not just below the boot top. In fact, there should be seacocks on all penetrations that could become immersed during any condition of loading, heel, and trim.

Also make sure that each seacock is really a seacock, which is defined by the American Boat and Yacht Council as "a type of valve ...operated by a lever-type handle...[that moves] through a 90-degree arc, giving a clear indication of whether it is open or shut." If you find a multiturn (ball) valve installed on a through-hull connection, replace it with a proper seacock. A seacock should be attached directly to the through-hull fitting. If a pipe or tube is installed between the through-hull and the seacock, it creates a possible failure point that is unprotected by the seacock.

Use It or Lose It
The best preventive maintenance for seacocks, whether made of plastic or metal, is to periodically open and close each valve. Leaving a valve in one position for a period of time without moving the handle can allow it to freeze up. Manufacturers' guidelines differ slightly, but the consensus is that you should move the handle of each seacock throughout the full open-close path at least once every 30 days, more frequently if possible. One school of thought advocates shutting all seacocks each time you leave your boat unattended. If you follow this diligent strategy, be just as methodical coming back aboard, especially to make sure valves on the raw-water intakes are opened before starting the engines. More than one of my acquaintances hangs a placard on the ignition switches as a reminder.

If you have a seacock that won't operate freely, you'll need to disassemble and lubricate it. To lubricate seacocks while a boat is in the water, Forespar Products Corporation recommends the following procedure:

1. Close the valve.

2. Remove hose or tubing from the inboard side.

3. Drain any remaining water from the inside of the valve.

4. Swab some waterproof grease on the inside of the valve mechanism.

5. Reattach hose or tubing, checking clamps or fittings.

6. Activate the valve several times to spread the grease.

When the boat is hauled, perform steps four through six from outside the hull to lubricate the opposite side of the valve mechanism. Use winch, wheel bearing, or water-pump grease. Avoid lithium or other metal-based greases, which may cause galvanic corrosion.

If a seacock is completely frozen, it's best to haul your boat before attempting repair or replacement. If it's not possible to haul out the boat, then temporarily plug or seal the through-hull connection from outside the hull before attempting a repair. Don't be like the guy we heard about, who sank his boat at the dock while doing battle with a stubborn seacock. The handle wouldn't turn, so he put a 20-inch Stilson wrench on the valve stem for leverage and proceeded to rip the entire valve off the through-hull fitting.

It's the "little things" like this that can ruin your day.

George L. Petrie is a professor of naval architecture at the University of New Orleans and provides maritime consulting services. His Web site is

Next page > One Good Turn, Part 1 > Page 1, 2

This article originally appeared in the May 2003 issue of Power & Motoryacht magazine.

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