PassageMaker - March 2012

WHAT’S WRONG WITH THIS PICTURE

SEACOCK DESIGN AND
INSTALLATION

Few would argue that the reliability of through-hull fittings, seacocks, and below-the-waterline plumbing demand every boatbuilder’s and repair yard’s (and vessel owner’s) greatest level of attention. Yet, on so many occasions I encounter components that are poorly installed, in a manner that not only fails to meet standards established by the American Boat and Yacht Council, they also defy the instructions from the components’ manufacturers as well as—in many cases—simple common sense.

When it comes to critical raw-water plumbing (which I define as any plumbing that if breached, would cause flooding, or worse, would allow water to be pumped into your vessel) the standards must necessarily be high as the consequences of a failure could be catastrophic. A 2-inch hole, failed hose, or through-hull fitting 2 feet below the waterline will admit over 100 gallons per minute, and that rate will increase as the vessel sinks deeper.

In other cases, I encounter elaborate and extensive, yet fragile,

raw-water plumbing systems used for air conditioning systems and reverse osmosis watermakers. Installations of this sort are often marked by extensive use of plastic nylon or PVC plumbing fittings and clear PVC hose, components that are not designed by their manufacturers to be used in raw-water applications.

In plain terms, ABYC guidelines
call for seacock installations that
must be able to withstand 500
pounds of static force for 30 seconds
without failure. They also specifically
call for full thread compatibility
between all components. That is,
NPT (tapered) and NPS (straight
threads) can only be used with like
components. While I
agree that sounds like
common sense, mixed
thread installations are
present on fully one-
third of the vessels I
inspect. Where raw-water
plumbing is concerned,
there’s one more
requirement in my
book: If I can’t stand
on it, it’s likely not
strong enough.