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posted to rec.boats.cruising
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First recorded activity by BoatBanter: Oct 2006
Posts: 878
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Fuel usage
Roger Long wrote:
OK. 30 foot waterline at 5 knots would be a speed length ratio of .91.
My boat should be fairly similar in characteristics, heavy but with a
modified keel. Look at the graph towards the middle of this page:
http://home.maine.rr.com/rlma/StriderFuelSystem.htm
Waterline length of my boat is 26 feet so equivelent speed would be 4.64
knots. She reaches that speed at 1560 RPM with 4 POB. Horsepower at
that RPM is only 4.2.
Displacement is 13,500 pounds or 6.03 Long Tons so .70 HP/ton. Your
displacement is 18,000 or 8.03 tons so you need 5.59 HP to go 5 knots.
.056 gallons per HP per hour is typical for most diesels so you would
burn .31 GPH. This doesn't sound like much but you are talking about a
pretty slow speed.
At an economical speed length ratio of 1.15, typical cruising speed for
most sailboats, 6.3 knots for your boat, you would be burning a bit over
twice that. At a speed length ratio of 1.29, flat out, you would be
burning about 4 times that.
Appreciated!
Gordon
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