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Old 11-05-2015, 02:26 PM   #184
Ski in NC
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City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
Quote:
Originally Posted by TDunn View Post
My boat is a pure displacement hull with a 32' waterline which gives a nominal waterline speed of 7.58 knots. The boat also has only an 8' waterline beam and displaces 9500 pounds. The small displacement, high length to beam ratio and hull form result in a very easily pushed boat up to around 7 knots. 7 knots is the transition point where the boat starts needing a lot more power to move it faster. At 7 knots I have almost no wake. All the calculations show that I should need just over 10 hp to make 7 knots. Note that 9 knots requires a fuel burn of about 2.4 gph. Of course it is your choice to not believe it.
TDunn- Calling BS was a little harsh, I appologize for that. But your numbers do not pass the smell test. A 2liter diesel at 2000rpm will burn around 0.2- 0.3gph at no load, i.e., neutral. Then at 0.55gph that leaves little to make propulsive power. Your boat may only need 10hp to push, but at 2000rpm it's going to take more than 0.55gph to do it.

It is possible you have both a super efficient engine and a super easy to push boat, but to believe it I'd have to see good hard numbers.

How have you arrived at your 0.55gph number?

And again, kudos on the old cruiser..
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