Re: Choosing An Outboard
To the last question: No, not all boats are displacement hulls. Most of the boats owned by people on this forum are planing hulls. They run at displacement speed, until enough power is provided to lift the bow out of the water and allow the boat to run with just a small portion of the hull in contact with the water.
Displacement hulls won't plane, no matter how much power you push them with. They cut through the water, rather than riding on top of it. Displacement hulls have what is called a displacement speed, which goes higher in proportion with the length of the hull. So, a battleship can go faster than a tug boat because it's much longer. Applying more power than is needed to operate the boat at its displacement speed will only speed the boat up a small amount, so is wasted.
So, the question of how large an outboard should be used on a displacement hull is a very apt one. It takes a surprisingly little power to reach displacement speed on such hulls.
I can't answer the OP's question, though, because I'm not familiar with the design of his boat. His best guide will be through the manufacturer or by comparison with other boats with similar hull designs.
