My buddies Pontoon boat will do 35kts using a 115hp outboard. It's larger than a 18' cat and uses, what to me looks like 55gal drums with a pointy front. It's definitely not planing, and I bet it's above hull speed. I've seen pontoon boats on Lake Norman here in NC that goes a lot faster than that, people even wake-board behind them here. I guess with enough engine you can make anything move.