By Tom Burden, Last updated 6/25/

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Water-cooled inboard engines inject cooling water into the exhaust pipe, which cools the exhaust and muffles engine noise. The exhaust then pushes the water out the exhaust pipe. This is known as a wet exhaust system. Wet exhaust systems have the advantage of using the heat-absorbing and sound-dampening qualities of water to cool and quiet the exhaust. Air-cooled, or dry exhaust, systems are uncommon except in performance powerboats or large work boats where excessive heat buildup and/or noise are tolerable, or in precisely engineered trawler/passagemaker exhaust systems which insulate the hot exhaust pipe with forced air.

Above- and below-waterline applications require distinctly different products to muffle engine noise. Powerboats use marine mufflers, commonly made out of non-metallic materials, to contain engine noise and cool the exhaust. Mufflers are always mounted above the waterline, and usually have some sort of check valve in-line to prevent backwards water flow, which might damage the engine.

Lift mufflers like Centek Vernalifts are used both by powerboats and sailboats. They are vertical mufflers mounted below the waterline with an outlet line coming off the top of the container. Exhaust gas and expended cooling water are mixed shortly after the exhaust manifold and travel together into the muffler's chamber where the cooling water collects before the exhaust gas pressure pushes it out the remainder of the exhaust hose. The mufflers's chamber also provides a place for seawater from following seas to collect if the boat is running under sail. For greater quieting, an inline muffler can be used downstream of a lift muffler.

Additional System Components

For vessels with through-the-transom exhaust, there are flapper valves that prevent following seas from running back up the exhaust system and flooding the engine. They clamp around the outside diameter of an exhaust pipe to form a check valve.

Exhaust hose or tubing is used to connect the exhaust manifold to the muffler and runs from the muffler overboard. It is essential to use material which can withstand heat, oil, acids, pressure, water weight and vibration without failure. As a rule of thumb, hose runs that are longer than four times the inside diameter of the hose should use wire-reinforced exhaust hose or fiberglass exhaust tubing. Shorter lengths can use non reinforced hose. All hose connections should be made to rigid surfaces (such as tubing, pipe, or the muffler itself); hose-to-hose connections are never recommended.

Soft wall vs. hard wall wet exhaust hose.

Discussion in 'Inboards' started by missinginaction, .

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   missinginaction

   I did a search but did not find anything on this topic.
   
   I'm in the final stages of a restoration of a Silverton sedan. As part of this project I've refreshed a low hours 302 Ford and replaced the old cast iron mufflers with Centek Vernatone mk II's.
   
   Since it's a v-drive the exhaust runs are short, no more than about 18 inches.
   
   Does anyone know the advantages of hard wall hose vs. short wall? The runs to the transom are straight and the only bends would be very slight.
   
   Any input would be appreciated.
   
   Thanks,
   
   MIA

    

   missinginaction,#1

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   If you want to learn more, please visit our website marine exhaust hose.

   keysdisease

   Do you mean with or without wire reinforcement or corrugated vs smooth?
   
   For such a short straight run I would use exhaust rated smooth no wire hose like the 200 series here:
   
   http://www.teleflexmarine.com/products/hose/engine-hose/
   
   or the 110-200 series here:
   
   http://www.tridentmarine.com/stage/wetex_hose.htm
   
   You could move up to silicone as a upgrade, and for small lengths the cost might not hurt too much. I don't like wire in exhaust, I've seen too much of it rust or corrode and cause issues. It's fine on intakes to reduce chance of collapse but exhaust gasses are like way corrosive.
   
   Steve

    

   keysdisease,#2

   1 person likes this.

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   missinginaction

   Thanks for the reply Steve,
   
   That Teleflex site is very helpful.
   
   I'd probably use hose without wire reinforcement. Seems to me that wire prevents collapse under vacuum but this hose is under pressure and not a lot of it. The boats set up for twin mufflers and with 3 inch I.D. hose there won't be much back pressure on the system.
   
   I'd probably use smooth wall. I was just curious as to why there are two different types, hard wall and soft.
   
   I'm trying to decide which to buy.
   
   MIA

    

   missinginaction,#3

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5. Frosty

   Previous Member

   Wire stops kinking. Carry on with your smooth wall.

    

   Frosty,#4

   1 person likes this.

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