T&T: Fuel Usage

[Robin Brueckner]

Rich posted "....8.1 knots at 3.9 GPH and 5 GPH at 8.6 knots....Assuming
a speed increase is proportional to hp (and fuel consumption) cubed:

taking the ratio of speeds 8.1/8.6 and cubing would suggest a fuel
savings of about 0.83 (savings of about 17%)... .83 x 5 GPH is 4.2 
calculated instead of his 3.9 actual... quite close considering unknown
factors such as currents, winds, and sea conditions....

J&M posted: "...."weight" (as weighed on a lift and DISPLACEMENT (the
weight of the water displaced) can be very different-that is where hull
shape becomes a factor...."

Both aspects of that statement are incorrect. (Archimedes discovered the
relationship.) A 40,000 lb boat always displaces 40,000 lbs of
water...while afloat....regardless of hull shape, regardless of whether
fresh or salt water....But  this displacement is different than a
calculated "tonnage" for USCG documentation purposes.

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