RE: Rookie needs Help/Advise on fiberglassing a Balsa/Ply Hydroplane
Stresses on the red areas are not going to be as high as those in areas where you will realistically see loads applied. The side sponson where the turn fin is mounted will see probably the most of the whole boat. Also where the sponsons attach to the hull. Also dependong on what you are using for motor support additional support on that big flat hull where the cmounts will be, the cable will exit and the transom where the drive and notably the rudder are to attach will all see their share. Also if you want the hull to survive a flip you want to strengthen all you want to survive a water impact. While this adds weight - you can afford a little more than the plane guys will consider.