3” exhaust on 37’ PSC - SailNet Community
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post #1 of 9 Old 12-17-2018 Thread Starter
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3” exhaust on 37’ PSC

I’m repowering my 1991 37’ PSC. Going from 2” to 3” exhaust. Has anyone out there already been down this road that has a good solution? I’m familiar with the Vetus (and other’s) schematics as to how to properly install a wet exhaust system. The challenge is to how to optimally shoe horn such a large system into the small area behind the new Yanmar 4JH5E. Thanks in advance
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post #2 of 9 Old 12-17-2018
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Re: 3” exhaust on 37’ PSC

Welcome to SailNet! I'm sure someone will come along with some good ideas. I don't know enough to give any advice. Out of curiosity, why did you decide to go to a larger exhaust?

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post #3 of 9 Old 12-17-2018
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Re: 3” exhaust on 37’ PSC

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Welcome to SailNet! I'm sure someone will come along with some good ideas. I don't know enough to give any advice. Out of curiosity, why did you decide to go to a larger exhaust?
Or why a 54HP +/- motor on a 37 footer?

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post #4 of 9 Old 12-17-2018
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Re: 3” exhaust on 37’ PSC

Besides the engine being a bit big for the boat, there is no reason to go that large on the exhaust piping. the back pressure from the exhaust is a result of the height of the water lift muffler to the exhaust outlet of the boat, the inches of water that the exhaust has to lift. going to a bigger pipe is not going to lower the back pressure at all. The larger the exhaust size the more water that will be stored in the exhaust and the more water that could flow back to the engine when shut down or when the boat is heeled over. a bit counter intuitive but the smaller the exhaust line is for a given size engine the better the water cooled exhaust works.

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post #5 of 9 Old 12-17-2018
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Re: 3” exhaust on 37’ PSC

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Originally Posted by overbored View Post
Besides the engine being a bit big for the boat, there is no reason to go that large on the exhaust piping. the back pressure from the exhaust is a result of the height of the water lift muffler to the exhaust outlet of the boat, the inches of water that the exhaust has to lift. going to a bigger pipe is not going to lower the back pressure at all. The larger the exhaust size the more water that will be stored in the exhaust and the more water that could flow back to the engine when shut down or when the boat is heeled over. a bit counter intuitive but the smaller the exhaust line is for a given size engine the better the water cooled exhaust works.
However if Yanmar specifies a 3" wet exhaust, and you don't have that, they can give you a very hard time on warranty.
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post #6 of 9 Old 12-17-2018
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Re: 3” exhaust on 37’ PSC

I have a Yanmar 4JH4AE 54 HP on my Nonsuch 36. Welcome the extra power it has for head winds and currents here in the Northeast, it has a 3" exhaust installed with the engine in '09, no problems.
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Re: 3” exhaust on 37’ PSC

My old tired Yanmar 4JH2E mixing elbow has a 2” outlet on exhaust elbow. The new Yanmar 4JH5E has a 3” outlet on exhaust mixing elbow. The weight and foot print of the two engines are almost identical. I’m no engineer, but those that are tell me that reducing/staying with my current 2” exhaust system will cause the engine to run hot at the higher power settings. There is an interesting thread on the “cruiser’s forum” that is worth a look.
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Re: 3” exhaust on 37’ PSC

Would love to see some pics of S/V Caper Nonsuch’s exhaust system just aft of engine.
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post #9 of 9 Old 12-18-2018
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Re: 3” exhaust on 37’ PSC

Old Crow, I don't have any pics of what you want. I can tell you Caper is a V-drive, so the hose exits the elbow does a 180, runs to a water lift muffler, then to a loop and out at the stern. Should I remember the next time I'm at the boat (on the hard for the winter) I will get a picture for you.
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