Thread: GPH Information
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Old 12-31-2014, 03:23 PM   #14
CaptTom
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City: Southern Maine
Vessel Model: Prairie 36 Coastal Cruiser
Join Date: Dec 2012
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Quote:
Originally Posted by Richard W View Post
Agreed ... GPH ... a common shorthand and misconceived expression of fuel efficiency. My (planing) boat/engine is more fuel efficient at 13 GPH than at 3 GPH ... when you consider the distance covered over the time (speed).

30 MPH / 13 GPH = 2.3 MPG ... at 3300 RPM
6 MPH / 3 GPH = 2.0 MPG ... at 1000 RPM
This is one of my pet peeves. In the old days before GPS, fuel flow meters and reliable speed logs, when most boats were full displacement hulls, you used GPH because you always set your throttle for a certain RPM using the tach. After factoring in the effects of wind and current, you'd always go the same speed at a given RPM, burning fuel at the same rate.

GPH was a handy number to know back then.

Now, we always know our speed with a high degree of accuracy. We can calculate exactly how far we can go on a given amount of fuel. The number we really care about is MPG (statute or nautical, whichever you're using.)

So why does everyone still go around talking about X GPH at Y knots?

Don't make me do the math, just tell me how far you can go on a gallon at that speed!

Sorry. I'm done now. Thanks for letting me vent.
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