Uh oh, you need more pictures and LOTS of them!!!
Check the hull-
The rear part of the boat hull is super sharp and flares away from the tail section drastically.
I'm not 100% sure but usually flyingboat hulls have sharp edges where there are steps...but that's just a guess. I see your drawing indicates a rounded edge where the vertical step meets the rear boat hull. I think the sharp edge would be rearward from that curve.
What a killer shape!