Vented loop in exhaust?

[Jon Dodge]

I finally put my new engine in last weekend. My old engine had a vented loop in the exhaust. However, it was of poor qaulity, in poor condition and appeared to have been added on later. I don't know if one is necessary in the boat. Usually they are recommended if the water injection to the exhaust is below the waterline or less than 6 inches above the waterline. It seems that on the Hunter 31 with the Yanmar it is very close to 6 inches above the waterline. Is it necessary? Was a vented loop originally put on the boat? Thanks.-Jon

 

[Steve Dion]

Yes

Jon:I have a 1985 H'31. There was a loop on the boat originally. It may have looked cheap but they worked. I still have the original. If you want a new one, you may want to look at the Vetus loop. If you are spending $6k on a new engine, why take any chances?

 

[Jon Dodge]

Thank you Steve! (nom)

nm

 

[Ralph Johnstone]

Jon, Not Too Clear ...............

........ if you are actually referring to a "vented loop" or simply a loop well above the water line at all levels of heel. The vent on the loop would be used to prevent siphonage into the water lift muffler and engine but this is not possible as the engine is dead ended. Our 1999 H310 has a loop (with no vent)and as Steve Dion had mentioned, it's cheap insurance even if your engine is above water level. The loop in ours is nothing more that a large loop in the wet exhaust hose which rises about two feet above the water line before exiting the boat ........ underwater, if you can figure that one out.Regards,s/v Island Hunter

 

[Jon Dodge]

I'll try to clear it up

The raw water pump supplies the engine with cooling water. After it is used it is then injected into the mixing elbow. The mixing elbow is attatched to the exhaust manifold and "dry exhaust" feeds into it. When the water is injected at the mixing elbow you now have wet exhaust. This raw water exiting the engine runs through a hose to the mixing elbow. If the waterline circumstances mentioned in my original post exist and if the impeller in the raw water pump does not always seal absolutely perfectly a siphon can develop. When this happens the engine will fill with seawater through the exhaust manifold - there is no "dead end" to prevent this. A vented loop in the above mentioned hose will prevent this.In short, my question had nothing to do with waterlocks or loops in the wet exhaust system itself. Hope that clears the clouds.Thanks again to Steve, I like cheap insurance, just wanted to see if it was necessary first. I have used Vetus products several times in the past and have been very happy with them. I plan to put in the Vetus vented loop. In the meantime I'll keep the seacock closed.ThanksJon