| Is there such a thing as a formula into which I can feed specs on a boat
such as size weight, prop pitch, engine HP, etc. that would help estimate fuel
consumption, or is a sea trial the only way to figure it out? We bought a boat that is in
the yard for a refit and are wondering if we need to install additional fuel tankage,
since now would be the best time. >
Thanks for your time!
Our answer:
Fuel consumption is actually a factor of the engine
itself and it's design. Knowing what that engine is in and/or what it is doing isn't as
important as knowing how far you open the throttle. Even though electronic fuel injected
motors are more efficient at some rpm ranges, they often consume the same amount of fuel,
at full throttle, as a carbureted engine of the same size and horsepower. Also note that
many engines return a 40% fuel saving when operated below 3/4 throttle.
The formula you are inquiring about concerns three basic
items: Gallons per hour of the engine, Cruising speed of the boat, and Desired cruising
range.
( Fuel Capacity / Gallons per hour X Cruising speed =
Cruising range )
GPH specs can usually be obtained from the engine
manufacturer and/or can be loosely calculated by using the pounds per hour chart enclosed.
Remember fuel weights about 7 pounds per gallon. This chart
assumes perfect conditions. You can reduce the actual fuel consumption by about 18% for
most applications.
Determining approximate hull cruising speed, (if not known)
is a bit tougher.
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