Properly
trimmed and on plane, the ideal cruise speed (with best fuel economy)
may be several knots or mph higher than the boats natural planing speed.

Doesn't that contradict the law of physics?

"On plane" can be a question of degree, but once the drag from the surface has
reached its minimally attainable amount, adding additional speed, especially
through a single speed transmission, will burn fuel *less* efficiently.

I'll go along with "the ideal cruise speed" may be several knots faster than
the speed at which a vessel achieves plane, but I can't buy into a theory that
states fuel economy improves with increased engine rpm (after the vessel is on
plane, properly trimmed).