Re: What's wrong with this setup?
Correct WOT range on both of those motors is probably 4500 to 5500 rpm. As long as the prop pitch is the same on both props, the motors are going to run at the same rpm with similar throttle input. Where the problem usually comes into play with motors of significantly different hp ratings is in the props, because smaller motors sometimes have props of much less pitch. That causes the stronger and much larger motor to "drag" the smaller motor along, which in turn causes the low pitch prop to wind it up beyond its recommeded rpm limit.
The real problem here is in asymmetric thrust, because the small diameter prop on the 20hp, which will also have a shorter blade "chord," will provide significantly less thrust. This can be overcome by mounting the smaller motor further away from centerline and/or toeing the motors differently, through adjustments in the steering system.
I do agree that the arrangement would work better with short shaft motors - look at how far below the transom the cavitation plates are. The boat would most likely go faster with short shaft motors.
I think the boat hasn't sold simply because most people would find the setup to be a little "weird."
