I’ve seen sailboats with their chainplates bolted right through the fiberglass hull. That is not how we are doing the chainplates on our Dix 43.  Robert at Alumar devised some very sturdy components as part of his kit. The huge gussets, cut from 3/8” (10mm) plate, span the top two stringers under the side decks.  The actual chainplates are  3/4 x 2-3/4”  ( 3/4 x 5-1/2” for the center double one) that pierce the deck and are welded  to doublers below the deck, and then to the gussets. I calculated the angles of the various shrouds from the sail plan and attempted to align the gussets with these angles. This only worked so far, due to constrictions caused by the frames. By orienting the fore and aft chainplates athwartship and the two center plates in line, and also by adding a slight bend to the plates, I was able to make the top business end of the plates have alignment angles that should be very close to the shroud angles, thus keeping the load pulling in a straight line rather than at an angle to the hole. Even using a toggle connection on the lower end of the turnbuckle,  this is best, keeping forces on the pin evenly spread. The hole will be bushed with  a G10/ FR4  phenolic sleeve to keep the stainless steel pin from galvanically reacting with the aluminum, and also to act as a bearing to reduce wear.