T&T: Exhaust

[Robin]

Trainman captured many of the pros and cons of wet and dry exhausts nicely.

 A dry exhaust  (stack) simply replaces a wet exhaust riser and stern exhaust.
Wet exhaust riser failures (leaks) cause salt water cooling water to dribble
down into valves and cylinders and can kill an engine.

This problem is almost eliminated when turbocharged diesels are involved
because usually the wet risers are eliminated to permit hot exhaust gases into
the turbo to drive it. Water is injected after the riser hump, a nice
advantage. But both turbos and dry exhausts introduce a (minor) potential fire
hazard via uncooled apparatus.

If a dry stack engine installation is still salt water cooled via an intake,
engine mounted impeller pump and internal heat exchanger assembly, further
advantages are lost. For example, a plastic bag stuck on an intake can still
ruin your day, seacocks are employed, it takes additional power to run the
salt water pump, and winterization is required.

But a disadvantage of a keel cooler is that it can be damaged by an submerged
(floating)  object or perhaps minor grounding that would not otherwise affect
a boat/hull. Guards at the front of the keel cooler can reduce, but not
eliminate, the hazard of damage by floating objects. Some are mounted within
protective U channel frames.

Overall,  dry stack and keel cooler advantages outweigh traditional salt water
cooling when space and asthetics permit: that's why almost all commercial
boats have keel coolers and dry exhausts.