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

PART SIX: PLUMBING SYSTEMS WITH NOTES ON FIRE SUPPRESSION

allow two useful things: flushing the engine-

cooling system or drawing antifreeze through

it, and teeing to a bilge suction so that switch-

ing the seacock off uses the engine-cooling

water pump as an emergency bilge pump.

(Figure 17-4 shows this schematic.) Groco

makes an off-the-shelf fitting specifically for

this purpose and also the Groco SVB Safety

Seacock, which has the side-port inlet built

right into the one-piece seacock itself.

When using a metal seacock on a metal

hull, the seacock must be galvanically iso-

lated from the hull. Bronze can be used on

steel hulls (when isolated) but never on

aluminum hulls. Stainless steel seacocks can

be used on either steel or aluminum hulls, but

still have to be completely galvanically

isolated. The isolation must be complete: a

pad or gasket at the mating surfaces, bush-

ings around bolts, and washers under bolt

heads—no metal part in contact with the

seacock can be in contact with the hull,

period!

For passenger vessels, the U.S. Coast

Guard wants to see a flanged valve through-

bolted to a metal “spool” welded to the inside

of the hull. You can see this in Figure 17-5.

Insulating pads and bushings should be

Micarta, or a similar material that has a

reasonably high-temperature resistance and

moderate fire resistance. This entire assem-

bly, the spool plus through-bolted flanged ball

valve, forms the seacock and is not really an

off-the-shelf seacock; rather, it has been

fabricated by the builder. This is why on

commercial boats these are more frequently

termedsea valves.

Required Seacock Location

ABYC H-27 used to require that seacocks

be fitted on all through-hull fittings (sea

suction and outlet) which are below the

highest heeled waterline. This was arbitrar-

ily defined as 7 degrees of heel for all

powerboats (Figure 17-6), but for sailboats,

it meant that seacocks were required on all

through-hull fittings up most of the top-

sides. (You can see why this would be by

Figure 17-3.
Safety seacock
(Courtesy Groco)

Figure 17-4.
Seacock service
port schematic
(Courtesy Groco)