Almost any boat with an engine (outboards
excluded) and virtually every boat with
mechanical systems, such as refrigeration or
air-conditioning, generators, compressors,
deck washdowns, live bait wells, and so on,
needs to take in seawater for this equipment
to function properly. The piping related to
this is called sea suction or seawater intake
(even in fresh water), or raw-water intake.
This raw-water intake is integral to engine
cooling and exhaust, as we saw in Chapter 7.
Fundamentally, sea suction requires an
opening in the hull below the waterline. Obvi-
ously if something goes wrong here, you have
a serious leak. Further, the sea suction has to be
set up to provide adequate water supply, to not
clog, and to be properly inspected and serviced.
The fitting that penetrates the hull is called a
through-hull. On aluminum or steel commercial
vessels and large yachts, it may be a flanged
valve bolted on a metal “spool” instead. Simple
through-hulls are adequate well above the wa-
terline, but near or below the waterline, valves
must be used to close off any water flow in case
of emergencies, as well as for maintenance and
repair. These are termed sea valves or, more
commonly on boats, seacocks.Seacocks
The Terrible Gate Valve
Perhaps the most inexcusable culprits
responsible for boat sinkings are the brassgate valves that, instead of proper seacocks,
are fitted to through-hulls. A surprising num-
ber of low-cost production boats arrive from
the factory so fitted. Often, a do-it-yourselfer
will install a gate valve instead of a new sea-
cock because it’s a few bucks cheaper. Gate
valves are cheaper, occasionally much
cheaper, but they corrode and either freeze
open or break off—an instant disaster!ABYC’s Seacock
Standard: H-27
Under ABYC H-27, seacocks should have a
quarter-turn operation in which the handle
position gives clear indication of whether the
seacock is open or closed. The seacock can
be bronze or stainless so long as the alloy is
highly resistant to corrosion in seawater.
(I recommend bronze over stainless in all
applications—except on metal hulls—as stain-
less is potentially susceptible to pitting corro-
sion.) Reinforced plastic is also acceptable,
but a critical requirement is strength. Any sea-
cock must withstand 500 pounds (227 kg) of
static force applied to the end fitting in the
direction that the seacock may be weakest.
This is like two really hefty men standing on
the end of the thing! No ordinary plastic will
survive such loads, but this strength is critical
to ensure watertight integrity. As far as I’m
aware, the only plastic seacocks to meet
these requirements are made of Marelon, by
Forespar.Part Six
PLUMBING SYSTEMS
WITH NOTES ON
FIRE SUPPRESSION