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Old 10-10-2015, 09:34 AM   #10
Ski in NC
Technical Guru
 
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City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
Lots of boats are "overpowered" if you look at max engine output and compare it to actual cruising hp needed. But that is the wrong way to look at it.

What you really want is engine to be in a sweet spot on its performance map when the boat is in a sweet spot in its hp vs speed curve.

A Yanmar for example might be rated at 3300rpm, but it's best efficiency is actually at part load down around 2000rpm and mid load, well below its rating. So is that boat overpowered??

How much fun is it on a nice hull speed cruise with that beast down there doing 3grand? Sounds like a weedeater!!!

Good rule of thumb is to size engine so cruise speed is around max torque rpm for that engine.
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