TIME OUT!!
This discussion has wandered off into irrelavent issues.
The Weasel even had to do one of his juvenile trig calculations in a sad attempt to impress us.

There are many issues relavent to the depth of a hull while in the water. Some large some small.
My post was about one and only one issue - SQUAT.
That is the dynamic effect of a displacement hull riding lower in the water as related to the speed through the water.
It is generally a small factor when related to beach catamarans but can be important to large or heavy
boats.
Sorry Dave, but beach cats are displacement boats the vast majority of the time. On rare occasions they skip across the water as a planing hull. We have all skipped rocks across water, but I wouldn't call them planing hull shapes.

While not exactly correct, you can think of it this way; A displacement hull wants to ride at its normal waterline or displacement. When the hulls are dynamically pushing a bow wave it forms a trough. The hull still wants its waterline to match the water level next to the hull. It therefore has to sit "deeper" or closer to the bottom to achieve the same displacement. If the boat suddenly slows, the trough would collapse and the water rush in towards the "lower" gunwales.
Fortunately this is not a worry for beach cats.