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Old 01-10-2013, 11:04 PM   #72
Nomad Willy
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City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
Floyd I can see your concern about the noise. And about that I really don't know. But I've had some thoughts on noise over the years. I think basically most any engine we would use could be made very acceptably quiet w what ever amount of sound insulation was required to do the job. I should address that issue myself. At my normal cruise of 2300 I consider my boat plenty quiet enough. But at 2500rpm for an hour or more I get a bit tired of the extra noise. My boat has little sound insulation and I'm sure lots of my noise is coming from the air intake. So I need to make an intake silencer like the cars of the late 40s had.

But just how much noisier a high rpm engine is ..... I just don't know. I do know though that the higher the engine speed and the more cylinders the engine has the less vibration. And vibration is a huge source of noise. Many more strokes of less force and energy produce much less vibration unless there is a significant part of the boat like a bulkhead that is resonant to the engine frequency. Soft engine mounts absorb low amplitude higher frequency vibration well.

The sound of a diesel engine is frequently not an indication of how "happy" it is. I think the engines are "happiest" at a relatively high rpm and normal load.
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