I'm not too interested in SUP surfing, but I really enjoy flatwater paddling/cruising. Looking at a variety of production race/touring boards, seems that most companies are going with shapes that have fairly wide tails, displacement noses, and pretty square rails...but there's a few folks out there doing pintails, usually on 14'+ boards.
What is the design logic around the different rail and tail shapes for flatwater/cruising/racing boards? I'm assuming the square rails help keep the volume all the way out to the rail and maintain stability. Manueverability isn't really a major target, while stability is, I suppose. I'm assuming that a pintail would be more efficient on a long board, as it would let those flowpaths along the rail come back together with minimum disturbance, but on shorter boards would compromise volume.