On Friday 13 August 2004 3:08 pm in rec.boats Melandre wrote:

For example, I think we can agree that smaller 14' - 16' boats are
quite fuel efficient (compare to the 20+') and I am assuming that most
of these owners do not have to worry very much about how much they
will need to dig in their wallets at the end of a typical weekend.
At the other end, I seems to hear and read that essentially 25'+ boats
are fuel gulping monsters (0.5 to 1.5 GPM).

There are several factors involved here.
Firstly - all petrol (gasoline) engines guzzle more fuel than diesels.
Second - Planing hulls require enormous power and thus fuel.
Third, displacement speeds are proportional to the square root
of waterline lenth. Typical displacement speed is 1.3*len(feet)^2

As a typical data point, a 60 foot trawler with 2 x 650 HP CATs
will use about 10 gal/hour at 10 knots in displacement
mode or 40 gal/hour at 20 knots WOT. An 80 footer will actually
use rather less fuel for the same engines and speed.
This is a helluva lot less than small high speed planing boats.

Bigger and slower uses less fuel.
Planing is expensive at any speed.

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