I don’t know a formula.    I have a couple data points to muddy the water
(incorporate into your model).

My tohatsu sailmaster 6 has taken the Rhodes 25 n m at 4.5 knots uisng less
then a gallon in 1-2 foot confused chop.    There was no wind, or I wouldn’t
know this.  It was right after a carbourator rebuild.

On a 500 pound Chrysler dinghy my Evenrude 2 cylinder 4 hp 2 stroke can tow
another boat a mile at near hull speed but will only make it half a mile
back before emptying its 1.5 qt internal tank.    Again, I wouldn’t have
learned this if there was wind.   On the other hand it has suffered two
mechanical failures in 30 years, otherwise starting on the second pull every
time no matter the temperature, so I guess It’s efficiency may be hindered
by the fact it actually runs.   

Math by dummies.   

Alex



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Alex Cole
S/V Lark
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Sent from: http://rhodes-22.1065344.n5.nabble.com/