fuel efficient cruising

[Larryrsf]

My boat is a 74 V20 with an Evinrude 150. An outboard mechanic evaluated my engine and said it is in "new" condition internally, obviously from the compression numbers having had a recently overhauled power head. He said the carbs should be cleaned at the end of the season for optimum performance. I add the right amount of the recommended carb cleaner to the fuel tanks.

I have it in a marina on San Diego Harbor. It will be there until October at least. The harbor is usually choppy, making a very rough ride at higher speed than 20 MPH or so, when the boat is just planing.

How should I set the trim for best mileage? Obviously I start with it trimmed all the way down, which keeps the bow low enough to see over. But as it starts planing should I adjust the trim for optimum speed with the lowest RPM? It does 22MPH (accuracy of speedometer unknown) at 3000 rpm.

Obviously the smoothest ride is with the trim down and minimum speed to plane. But that may not be the most fuel efficient.

Larry