Rudder laminate

I have a few spade rudders to build this winter out of female tooling for 35 to 42ft typical 80s vintage IOR influenced sailboats and am wondering what would be a good laminate schedule, we will be doing a pro set epoxy laminate with 15 lb/ft3 epoxy expanding foam core with mild post cure so i expect/hope to pull some weight out of the things. Of course the old ones are lots of mat and roving.We will be using the existing shaft structure. In past rudders ive done ive used a lot of uni s glass and a few layers of double bias to take the axial loads, much of the load is taken by the metalwork. I may cut the old rudders apart and burn out the resin to find the old schedules after making the molds but what im after is something at least as strong but lighter. The other thing is what to do for gelcoat and skin coat when using epoxy, could we spray in 10mils of interprotect and use a light cloth skin coat or maybe no skincoat at all, ive never done an epoxy layup in female tooling.

Steve.

 

I'd recommend IMEDGE ECT-120 instead of a bond or tie coat. It saves steps, is better than gel coat and epoxy compatible (no paint). I can hear the poly guys screaming now . . . what do you mean better than gel coat. Well, almost 3 times the adhesive strength at room temperature and 4 times with post cure, far superior blush resistance (moisture resistance) and about 200% better abrasion resistance, plus far high elongation modulus, much higher gloss and gloss retention compared to gel coat also. Can be brushed (I never have), though designed to be sprayed and is the desirable in mold replacement for gel coat, with epoxy layups.

As to a laminate schedule, this shouldn't be especially difficult to work out, though an actual schedule, particularly if interested in saving weight should be done on a per application basis. A good start would be three or four units of 45/45 biax over your 15 pound foam. This is light, but can work, depending on your in blade armature. Uni dia's against the foam is a good option too, but again a reasonable schedule should be worked out on a blade by blade situation. It wouldn't cost much to have a laminate engineer work up a set of schedules for you.