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Old 07-13-2015, 05:17 AM   #5
FF
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Join Date: Oct 2007
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"For your fulsome and precise explanation. I was concerned because so much column inches have been used to explain that this boat or that is / was overpowered."

A multiplier of 1.3 vs 1.6 does not change the hull speed much.

Few cruisers will go hull speed as pulling back to a multiplyer of .9 to 1.15 will save 1/2 or 2/3 the fuel burn.

Another way to look at cheap power cruising is by realizing that most boats will cruise at under 3 hp per ton (2240 lbs per ton) maximum underway.

Most boat engines and the drive train is not optimised for cruise speeds so for many 15 hp per gallon of fuel is a close rule of thumb.

The Sq RT of LWL was measured on old fat boats L/B of about 3 , once the hull has a L/B ratio of over 6-1 the wave making becomes less important , with weight and skin friction surface area being more a factor.

Everything is a compromise , mostly to nital coat.

A CPP (controllable pitch propeller) would add $7,000 to perhaps $12,000 to the initial price and perhaps save 10% to 15% of the fuel bill, bit it would take a generation to see a saving.
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