In post 5 you replied with a length of 23" (584mm) I believe you are more familiar with mm and this may be the confusion??

I have a 685mm rigger that runs a 540 size motor on 2s. I have tons of room in it. For a hull over 550mm a 540 s motor is needed. A 380 XL motor performs similar to a 540 s motor and may be used. I place my cells over top of the second sponson boom in my 685mm rigger.

The front sponson on my 685mm rigger is about 30mm deep from what I can remember. When the hull is at rest only about 5 mm is above the water. The booms are submerged completely.
How deep the hull sits at rest has no relation to how wet/dry the hull runs when on plane. Riggers will sit very low in the water but they were not designed to look pretty just sitting there.

I don't understand what you said is 15mm wide. My hull has an inner wall to wall dimension of 75mm.

Photo is of my 685mm rigger before anything had been placed in it.

Ryan