What's Below Your Waterline?

Seacocks fall into the 'out of sight, out of mind' category for many boat owners ... until they are needed.

By Steve D'Antonio
Published: April 2014

ABYC 27.4.4 Seacock — A type of valve used to control intake or discharge of water through the hull. It is operated by a lever type handle usually operating through a 90° arc, giving a clear indication of whether it is open or shut, and is typically of the two following types:

  27.4.4.1 Flanged Sea Valve — A Seacock with an integral flange used to individually and securely mount the device directly to the boat hull structure.

  27.4.4.2 In Line Ball Valve — A Seacock designed to be supported entirely by the through-hull fitting.

  ABYC H-27.5.4 Seacocks shall be designed and constructed to meet ANSI/UL 1121, Marine Through-Hull Fittings and Sea-Valves.

"That's the way we've always done it and it's never been a problem." Those words, spoken by an experienced boatyard manager who'd overseen the replacement of all of the seacocks aboard a bluewater-capable sailing vessel belonging to one of my clients, are an unfortunate and all too common refrain where below-waterline installations are concerned. During my inspection of the vessel, I pointed out that none of these new valve assemblies met the requirements set forth by the American Boat and Yacht Council's (ABYC) Standard H-27 Seacocks, Thru-Hull Fittings and Drain Plugs. While they are technically voluntary, these standards offer an unbiased, third-party approach toward this all too vital installation. To be sure your below-waterline installations measure up, take a look at the standards — and what they mean — and then go check out what's below your waterline.

An acceptable "seacock" under the standard is a sea valve or in-line ball valve with a handle that shows whether the valve is open or shut and that meets American National Standards Institute/Underwriters Laboratory (ANSI/UL) 1121. While suitable for household applications like washing machines and garden hose spigots, gate valves, those that have round handles that are rotated several times to open or close, are not ABYC compliant and they should not be used for raw water applications under any circumstances.

ANSI/UL 1121.8.1 The components of a through-hull fitting or sea valve shall be formed of galvanically compatible materials having the strength and resistance to corrosion necessary to withstand intended and abnormal use to which they are likely to be subjected.

  ANSI/UL 1121.8.3 A part made of drawn brass or machined from brass rod containing more than 15 percent zinc shall be subjected to the 10-Day Moist Ammonia-Air Stress Cracking Test.

Note that ANSI/UL 1121 uses the words sea valve (another word for seacock) right in the title, and not simply valve. While there are hundreds, perhaps thousands, of UL-listed valves, which may be used for any number of purposes, there are precious few UL 1121-listed sea valves. The UL 1121 listing includes testing for thermal extremes, mechanical deformation, moisture absorption, vibration endurance, as well as chemical and UV resistance. It's rigorous to be sure and thus, any seacock that is ANSI/UL 1121 listed, and thereby also ABYC H-27 compliant, is virtually guaranteed to be robust, reliable and of the highest quality. While other seacocks may be of high quality and reliable, without the ANSI/UL/ABYC approval it's tough to be sure just what you are getting. Remember, "UL Listed" does not mean it is specifically rated for use as a seacock; the valve needs to say, "UL 1121 Sea-Valve."

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