Wet exhaust systems have decided advantages over dry
exhaust systems. They are quieter, cleaner and cooler;
and do not pose a fire or burn hazard (eliminating the
need for insulation beyond the water injection point).
Today, most pleasure boats with inboard engines (for
power, auxiliary, generator) have wet exhaust systems.
Typically, raw water is pumped
from the engine intake seacock and strainer; through
a heat exchanger, possibly oil
cooler(s) and water injection nipple or mixing elbow
at the exhaust manifold; and itâs dumped with
the exhaust gas (cooled from 1100° F. + to less
than 212°F. on most engines) into the wet
exhaust piping and out the stern. Most commonly the
latter is a combination of flexible rubber exhaust hose,
bellows & elbows; sometimes fiberglass or stainless
steel pipe (at least for connectors); and mufflers or
silencers. Flexible hose, bellows an elbows are easier
and simpler to run than rigid pipe. They are not subject
to corrosion or stress cracking; and they absorb more
engine movement, vibration and noise. While the highest
quality black rubber exhaust withstands maximum continuous
temperatures up to 250°F., some high performance
engines emit wet exhaust at 300° to 500° F.
Here only silicone rubber can be used.