A method and system for operating a marine vessel includes a cruise control module operating the marine vessel at a speed and a trim control module positioning an outdrive into a plurality of trim positions. A fuel economy determination module determines a plurality of fuel economies for each of the trim positions and determines an efficient trim position from the plurality of fuel economies for each of the trim positions. An operation control module operates the marine vessel at the efficient trim position. A trim tab position may also be taken into account for efficient operation.