Story And Photography By Steve D’Antonio
DESIGN & SELECTION
n the first installment of our two-part series on seacocks, we discuss the importance of accessibility
and proper design and material selection, as well as the established industry guidelines that govern
this vital component of cruising vessels.
It’s a sight no boat owner ever imagines he or she will see, except perhaps in a bad dream:
a 1-inch column of water spewing from a failed through-hull fitting and filling the cabin. If
that fitting is located 3 feet below the waterline, it will allow approximately 34 gallons per
minute, or 2,000 gallons an hour, into your hull—more than most bilge pumps or the
proverbial scared crew member with a bucket can handle. Most bilge pumps are rated as if
the pump is at the waterline and is operating at 13. 8 volts, an unlikely scenario unless the
engine or generator is running.
Whether you’re kept awake at night by such visions or not, the possibility of a failed
through-hull/seacock causing rapid down flooding is very real, and it exemplifies the need
for secure, well-engineered, UL Marine-approved, properly installed fittings below the
waterline. It’s also important to keep in mind that a “UL Marine-approved” label does not
guarantee that the components have been properly installed or are appropriate for the
application in which they’re being used.
Section H- 27 of the American Boat & Yacht Council’s Standards & Technical Information
Reports for Small Craft states that “all piping, tubing, or hose lines penetrating the hull below
the maximum heeled waterline, under all normal conditions of trim and heel, shall be
equipped with a seacock to stop the admission of water in the event of failure of pipes,
tubing, or hose.” (Note the use of the phrase “below the maximum heeled waterline”—I’ll
talk more about this in a moment.) There are a few exceptions to this rule: cockpit drains
that exit the hull above the resting waterline, as well as most engine/genset exhaust
configurations. Another exception was added when the standard was revised in 2008: hull
penetrations that discharge above the resting waterline and below the maximum heeled
waterline and use reinforced piping or hose that resists kinking and collapse.
This guideline as a whole is frequently ignored by boatbuilders, repair yards, and do-it-yourself owners alike. If a through-hull is located above the resting waterline, most folks
simply assume that no seacock is required. In truth, if a through-hull sits below the heeled
waterline, a seacock is required, unless one of the exceptions comes into play.
In order to comply with the above-recommended guidelines, it is important to clearly
understand the phrase “maximum heeled waterline.” On a sailing vessel, this demarcation
is defined as the level of the water on the hull when the hull is inclined to the level of the
sheer amidships. Any hull penetrations that are wet under these circumstances are
considered to be below the maximum heeled waterline. For power vessels, the guideline is
somewhat more lenient, encompassing hull penetrations that would be submerged if the