Re: tri-hull bounce
Paul...
1) I've seen you say that you get on plane with the motor trimmed all the way down/in, which is correct, but then you indicate that it porpoises with the motor trimmed down/in. I am assuming you trimmed out and it porpoised that way, too? Why I ask: Sometimes a boat will porpoise if trimmed down/in when running fast, because you are just slamming the bow onto the water, it bounces off, and then the cycle repeats. If this is not the case, move to 2.
2). My hunch: The motor height is going to have to be slightly different on that hull configuration. In my opinion, this is the most likely issue. That hull might require a slightly different than standard rule-of-thumb mounting height. Others have opined that it might be close to what would be considered 'normal', but my honest opinion is that your motors final height should be different than rule-of-thumb, because of the shape of the hull. It's not a true stepped hull; we know that. However, I do believe it requires the motor height to be mounted higher or lower than what is traditionally considered 'normal'. Boats with different types of water action off the back, due to the somewhat unique hull designs, often require some stray from a standard mounting height.