[bestclimb]

a speed through the water would be best to figure out the most efficient hull speed. Otherwise you are getting or loosing a little distance from the current. A calm lake early in the morning without much wind would be a good test for figureing out the most efficient speed. In my experience, the least throttle just after the boat breaks over on step is the most efficient. Just as you can feel it surge ahead.

If you know instantaneous fuel consumption, you can figure out MPG just by looking at your speedo. Get an E6B (whizwheel) to do the quick calculations.

Currents can be felt, and often change so mapping them out may not be a workable solution.

When flying I find that a decent technique is to throttle back with a tail wind, to take advantage of an airspeed with lower fuel consumption, then speed up with a head wind to limit the amount of time I am bucking the wind. On the river this would equate to minimum throttle to remain fully on step down river. Then some amount faster than that for the trip up.