"Short Wave Sportfishing" wrote in message
...
On Fri, 04 Jul 2008 11:39:02 -0400, Gene Kearns
wrote:

GPH is pretty meaningless when one wants to determine fuel consumed
per distance traveled. Miles per gallon is really what we want to
know, since that is a better measure of fuel economy. (Least fuel
consumed, per mile, is my goal, anyway.)

Please take no offense, but that doesn't make any sense.

You have to have a base calculation which would be gallons per hour
(actually I've been told that the true base is per minute) because
it's the only true way to measure fuel usage.

Thus, you use X fuel over Y time.

So what can be the variable in the equation - RPM. At low RPM,
G(used)PH goes down and when RPM rises, G(used)PH goes up.

Thus, at A revolutions you use X Fuel over Y time.

That cannot change - it's the base calculation.

Now from there, you can make whatever calculation you want - furlongs
per fortnight or miles per gallon - it doesn't matter because it's all
based on GPH. It can't be any other way.

Feed distance, time, and gallons consumed into the computer and out
comes MPG.

That's fine, but it's still the same number as GPH. You have still
used a certain amount of Gallons Per Hour.

You asked a question in another post:

Heading upstream in a 10 MPH current at 8 MPH would give what
sort of MPG???? Sooner or later the fuel tank would overflow...!

That's exactly the point of GPH - you have a known figure.

If your not making headway, you are still using fuel - GPH again.

There are simply too many variables to calculate MPH over water. You can use
a GPS log of total miles traveled to calculate MPG of a particular trip.
That won't necessarily compare to the same trip on a different day. You can
collect data and come up with averages if you want. That might be useful.
You can reliably chart GPH at given throttle positions and then convert
throttle position to approximate MPH(over water, not land). You and I are on
the same page but the other folks don't buy into what we are saying. No big
deal.