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post #6 of Old 12-14-2012
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Re: overpropped vs underpropped

I too have a max prop and a 4-108 Perkins that has a max continuous rating of 3600 rpm. One thing you need to check is the calibration of the tach using a photo tack. I found that mine was off quite a bit.

The standard wisdom is to set that pitch so that you can achieve that rpm rating at WOT.....I have not followed that wisdom and not suggesting that you follow what I did. I'm just relating what I have done. After changing that pitch and seeing how the boat performed under various setting(it's a 37 ft Tayana), I decided on a pitch that let me cruise at 6 knots at 80% of WOT. However note that my WOT is only 3000 and not the 3600 ....The only thing IMHO that I'm doing is not achieving the max hp that is available if I could go to the 3600rpm. I fail to see how that I'm lugging the engine or glazing the cylinders. I could be wrong, but I've been doing this since the engine was new back in 1985 putting an average of 60 hours per year for the past 28 years.
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