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Old 01-10-2015, 06:07 PM   #12
ranger42c's Avatar
City: Maryland
Country: USA
Vessel Model: 42' Sportfish
Join Date: Aug 2013
Posts: 3,937
Originally Posted by PAJones View Post
Ok, I have an 81 Albin 36 DC with a single Lehman 120. Based on a 31 foot 3 inch LWL, I figure a 7.5 knot hull speed. At an indicated 1725 RPM in calm water I get an indicated (via knotmeter and GPS) speed a bit over 7 knots. 1: does that make sense? 2: Do I need to run the engine harder now and again to avoid "underloading" problems? 3: am I thinking reasonably that I should be burning about 2.5 GPH (and thus getting a bit under 3 nautical mpg)? I see so many folks talking about 4 mpg and I just don't see it. I also see a lot about need to properly load the engine - and it seems to me that with 120 hp on my boat 80%+ load would require 2000+ turns which would be very inefficient.

Can't speak to your speeds or fuel consumptions, but...

How accurate is your tach? If you're relying on an analog tach, it may or may not be displaying true flywheel RPMs... so you might want to check that.

Disregard if you've already sorted through all that.

South River, Chesapeake Bay
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