Gene Kearns wrote:
..

For example, a boat traveling into a 15 mph current at 15 mph could
be
expected to get 0 miles per gallon, but would reasonably be expected
to burn Y gallons per hour developing the requisite horsepower to
maintain 15 mph....

So, Tom, I'm with you on this one, since we are traveling in a
movable
liquid and at the mercy of the wind. Get a totalizer... at least
you'll know where you stand and how far off shore you are likely to
run out of fuel....

--

You need to measure your speed with something accurate like a GPS - I
do rivers all the time (90% of my boating). I don't know anyone who
would have the error you're talking about, if they use a GPS for speed.