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Old 04-24-2012, 12:16 AM   #1
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Advice on a gen set muffler.

One of the things I had to remove to gain access to my strut backing boards was the gen set (7.7 KW diesel Westerbeke 1800 rpm 3 cyl.) muffler. It had an Onan steel waterlift muffler. As I don't think my boat has ever been in salt water, it was in good shape. But I plan to have it in salt water long before I am willing to revisit the muffler, so I plan to convert it to fiberglass or? The old Onan is about 15" in hgt and diameter. The gen set has a 2" od exhaust elbow that exits about a foot above the waterline. The muffler has about a foot tall riser pipe coming out the top. This is about 10" higher than the exhaust elbow. The rubber exhaust hose then runs down hill to exit the transom about 6" above the water. The exhaust line from the muffler back to the bronze thru hull is 1 1/2". My Westerbeke manual doesn't say much about exhaust size. The Centec Vernalift web site says I should have a 2" exhaust before and after the muffler. There chart says 1 1/2" is adequate for 10HP. 2" should be used up to 30HP. There is a big difference between 10HP and 30HP. They make no adjustments for RPM. My 1 1/2" exhaust seemed to work just fine.

I see that Verna Lift's come in several heights and diameters. Any difference in performance or noise? Is this a good choice? What is quietest? With the layout I had, the high point after the muffler is 10" higher than the exhaust elbow, do I run the risk of flooding the engine if I crank it excessively and it doesn't start? Is the 2" diamter exhaust important enough to change out the 1 1/2" bronze thru transon port.

So many questions.

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Old 04-24-2012, 06:12 AM   #2
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Craig, Lots of questions you have only very few answers I know. I have a 12kw onan with the fiberglass muffler you speak of. It has 1 1/2" hoses all the way around and I have no problems.

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Old 04-24-2012, 09:23 AM   #3
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Donít Drown Me is a Norther Lights publication that clearly lays out how a small marine genset should be installed.

While written for NL, the principles are the same for any small generator.

Itís a 2.25 mb pdf download.

Palm Coast FL
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Old 04-24-2012, 12:09 PM   #4
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I would not be concerned about the hose diameter but the height of the gen set vs. the muffler and the through hull so water can not back flow into the engine. So a water lift might be the best. Maybe a fiberglass of SS water lift?

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Old 04-25-2012, 09:43 AM   #5
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Fiberglass water lift

I have 1/12 on my Onan 15kw and although it doesn't seem to be restrictive , it does spray cooling water out rather noisily. In my case I'll go to 2" when ever it needs replacement.
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Old 04-29-2012, 07:06 AM   #6
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Changed my genset muffler the first year we had the trawler. It had an old steel muffler and SS risers. Bought a new muffler, hoses and clamps for less than the cost of repairing the SS risers which were rusting out.
I replaced it exactly as it was previously configured- same length on all risers and discharge hoses. Placed the new muffler on the same shelf as the old one.
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Old 05-02-2012, 06:46 AM   #7
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For a water lift muffler a larger diameter is better.

A larger diameter will lift with less back pressure than a small unit.

It will also hold more water volume in a crank/no start situation , before flooding the engine exhaust.


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