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

Separating the Water

Still another exhaust option is mixing the wa-

ter with the exhaust gases, as usual in a wet

exhaust system, and then separating the water

out again. Such water-separator mufflers

(Figure 7-28) are, comparatively speaking,

new, but they offer interesting advantages.

First, the process of separating the water

removes more energy from the exhaust, mak-

ing it quieter. Second, the separated water can

be dumped below the waterline, usually about

4 to 6 inches (100 to 150 mm) below, but no

more. The tail-end, gas-line portion of the ex-

haust automatically acts as an idle bypass.

Third, the tail-end gas line is now cool and a

smaller diameter than the standard wet

exhaust line. It’s much easier to run this—

usually as hose—for long distances and around

weird corners without heat, noise, or back

pressure problems. Like the North Sea exhaust

system, water separators can assist greatly

with engine installations near midships.

Figure 7-28 shows a Halyard water-

separator exhaust on one of my boat designs,

PART THREE: EXHAUST SYSTEMS

Figure 7-26.
Underwater
exhaust nacelle on
the Schnell boat
(Reprinted from
Fast Fightling
Boats, by Harald
Fock) Figure 7-27. Exterior view of the Cape

Dory’s underwater exhaust system

Figure 7-25.
Inboard profile of
the Cape Dory 40’s
underwater
exhaust. Item #9
is the idle bypass,
and #10 is the
underwater
exhaust.