A better, but not as sexy, term is a semi-displacement hull or high-speed displacement hull.
Certainly not planing, and not really wave-piercing, all boats go through waves, cats just tend to be influenced less by waves than regular boats because they are generally narrower.
It's just that nearly all cat hulls can "pierce" or "cut" through the most important wave: the front wave created at maximum displacement speed.
One question:
is piercing the front wave easier or harder than piercing other waves? The front wave moves with the boat, others move in other directions.
The front wave has a height related to the hull's displacement, others have any height.
The front wave travels at a well known speed, others travel at any speed.
The front wave is definitely special. But this does not answer the question, so lets think different:
If it was harder to pierce (or cut) through the front wave, most cats would be able to pierce waves. Since this is not the case, the front wave must be easier to cut or pierce.
Ok, I'm convinced: calling any cat a "wave piercer" is a BIG mistake. They are "front-wave cutters", "wave-cutters", "front-wave piercers", "high-speed displacement" or whatever better describes their particular method to cut through the front wave.
Now, cat hulls are closer to wave piercing hulls than planing hulls, that climb the front wave and ride it. And cutting through the front wave requires at least part of the features of a true wave piercer. So...
Why aren't all cat hulls built as true wave piercers? Due to lower payload only? Wave piercing is inefficient vis-a-vis some other mode? What are the reasons?
