Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

This strength requirement means that a
proper seacock should have a flanged body
to mount against the inside of the hull—not
simply a bronze or stainless quarter-turn
ball valve screwed to the inside tailpiece of
the through-hull. This, too, is common, and
though vastly better than a brass gate valve,
it doesn’t meet ABYC strength require-
ments. In fact, I prefer seacocks with
flanges that are through-bolted, as these are
strongest. Figure 17-1 illustrates a Groco in-
line, quarter-turn ball valve screw mounted
on a through-bolted flange base that is
screwed to a through-hull. These are the
features required for a proper seacock.
This happens to be a seacock made up of
two components (plus the through-hull),
but excellent seacocks from Groco, Wilcox-
Crittenden, Conbraco, Forespar, and others
are available as single units (plus the
through-hull).
I like Marelon seacocks (Figure 17-2)
because they are light and completely free
from galvanic corrosion problems on metal
boats. I use them frequently; however, I tend
to use only sizes 1^1 / 2 inch (38 mm) and up. My
concern is that in the smaller sizes, the valve

handle-stem (not the seacock itself) is a bit

too weak, particularly in cold weather.

No plastic seacocks of any type are accept-

able under CFR Commercial for passenger

vessels. These boats can use only metal for

its greater fire resistance.

Seacock Refinements

You can install a T-fitting just above the

seacock with a pipe or hose off the T to

Chapter 17:Sea Suction

Figure 17-1.

Correct and incor-

rect installation of

seacocks (Courtesy

Groco)

Figure 17-2.

Marelon seacock

(Courtesy

Forespar)