I didn't quite get what you meant about the tail rocker at 17 vs 30"?
Hi Benji, I mean that the location of the planning area which is also the max deepness of the concave is situated around 17'' from the tail on the SB. Once you scale up to a SUP 7'4" the max concave deepness comes up to 30 " from the tail.
So if you want to pump the SUP board as you would do it on an SB, you must have your foot stance aside of the 30" concave location.
IMO, to reply to '' Shortboard to sup ratio- calling you shapers" the reply is not to give a ratio but to make a whole SUP shape working as an SB shape. This makes me say that you cant simply scale up an SB shape to a SUP to make a good board. This is not as simple.
So I keep drawing and by now I'm working with the kind of concave bottom shape and rocker. 7'7'' 28" 100 litres with 5 fins FCS K2 Thruster with small leading twinzer fin.
Please, I want to ask your weight and height?