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When we mix exhaust gases with an engine’s discharge water, we cool the water enough to use rubber and plastics in the exhaust system. This is good because rubber and plastics also break up sound waves and act as an effective muffler.
But there are two problems: the increased back pressure from moving that water through the system, and the noise of constantly splashing discharge from the outlet. While that discharge flow is reassuring when we peer over the stern for the indicator that our raw-water system is functioning, it can also be incredibly annoying. Generators running at night to support air conditioning can splash at erratic intervals and, in a quiet anchorage, disturb the peace, even if the generator is soundproofed.
The back pressure created by using the exhaust as a pump limits the length of the run and how convoluted a system can be. A solution is needed for generators that have to discharge carbon monoxide or smelly gas high up in the air away from occupants, and for boats whose main engines have difficult runs, such as center cockpit yachts.
The exhaust separator must be mounted high up in the machinery space so that it physically divides the cooled gas from the discharge water. This setup allows for exhaust runs that otherwise would be too high of a lift or too restrictive for water to be mixed in. The cooling water has to be high enough up to drain from the separator, then run down through a connection hose to a seacock. These components must be sized correctly; I recommend using a temporary drain hose of clear vinyl so adequate drainage can be monitored at all operating loads and speeds.
Separators are safe and effective, but they must have adequate height and calculated plumbing to ensure complete drainage.
Roger Hellyar-Brook runs a marine consulting business, repairing and upgrading boats of all types. He has spent more than 40 years in the marine industry and is the former manager of the systems program at The Landing School in Arundel, Maine.
Paul Mirto is a digital illustrator, longtime boater and former Coast Guardsman. mirtoart.com
This article originally appeared in the May 2018 issue.