If it's a vessel that never had a capacity label then they would not be in violation as there is no horsepower label listed for the vessel. It would fall back on unsafe speed, movement, etc. if something happens. from above - (1) operates a vessel at such speed or maneuvers a vessel in such a manner as to endanger the life, limb or property of another person

I know some of the old wooden Chris Crafts from the 30's through the 50's had some monster V8's in them. I'm sure in today's equivalent boat they couldn't get away with the larger engine.