In a displacement hull boat there is no reason to add power betond what I have mentioned. If you are set up for hull speed +10 at maximum engine rpms, then added power simply over loads the prop blades and causes cavitation. To handle more power you need a bigger prop, or one with more blades, more pitch or a higher disk area ratio.

Given the 2.74:1 gear ratio he has, Larry can't turn his prop fast enough to go faster than about 10 knots, which requires only about 35 hp. If he managed to put his rated 59 hp intomthe prop, it would certainly cavitate because of excessive blade loading. You could put a 75 hp engine in your boat, but you could never use the power because you can't fit a big enough prop. Also, if you put in too much power, the engine never runs at a high enough fraction of its rated output during normal operation to avoid carboning up, glazing the cylinder walls.

Finally, a sailboat with a planing hull is far from normal