Doing It Right
As good as waterlift mufflers are, however, you
can’t simply jam one willy-nilly into the bilge,
run some hose to it, and expect it to work
properly. Like any exhaust installation, the wa-
terlift muffler must be set up to minimize back
pressure and to eliminate any possibility of
water finding its way up into the exhaust man-
ifold. Figures 7-12 and 7-13 show the two
basic layouts: when the muffler is located be-
low the motor exhaust outlet, and when the
muffler is located above the exhaust outlet.
THESTANDARDLAYOUT When both the en-
gine (or generator) and the muffler are
installed below the waterline, you need a
siphon break (also known as a vented loop,
see Figure 7-12) to prevent siphoning water
back into the engine. The loop should be at
least 18 inches (45 cm) above the waterline,
and sailboats need to be certain that the loop
is at least 8 inches (21 cm) above the highest
heeledwaterline. Generally, if the loop is high
and near the centerline, there’s no problem
here. If, however, the loop is way off to one
side—on a sailboat—you’ll just about have to
run it up to the deck underside or higher still
into the trunk cabin or cockpit coaming (see
the sidebar on vented loops).
The inlet to the waterlift canister from the
exhaust manifold has to be at least 12 inches
(305 mm) below the water-injection point.
There should be a downgrade of^1 / 2 inch for
each foot of distance (41.5 mm for each
meter) from the manifold outlet to the muf-
fler inlet. Ideally, the lift pipe (usually just
called the “lift”) out from the muffler should
be close to vertical, but this is often hard to
accomplish. The important consideration
here is to keep the lift height as low as prac-
tical to avoid excessive back pressure. For
most installations, a maximum lift—from the
bottom of the muffler canister to the top of
the lift—should be 42 inches (106 cm).
The greater the lift, the greater the back
pressure, so less lift or height is always better.
The catch is that standard practice recom-
mends that the center of the exhaust outlet be
at least 6 inches (15 cm) above the waterline,
and that, at the same time, there must be a drop
of 12 inches (30 cm) from the high point of the
lift pipe to the through-hull. The good news is
that in practice I’ve had installations that exited
the transom only an inch (25 mm) or so abovePART THREE: EXHAUST SYSTEMS
Figure 7-10. Inner
workings of a
waterlift muffler
Figure 7-11.
Waterlift muffler
installed