WORK­INGS Ex­haust sep­a­ra­tors pro­vide a so­lu­tion for boats with gen­er­a­tors and en­gines that have com­plex ex­haust runs.


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. Paul Mirto is a dig­i­tal il­lus­tra­tor, long­time boater and for­mer Coast Guards­man. mir­

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.

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