I'm in NZ, and completing an Italian design with marine ply frames like Sobrevida above is talking about, and it calls for stringers and frames to be glued and screwed. The screws are thin 6g stainless steel, and don't appear to hurt the frames, however in my opinion if you do this you must glue the joins also, because the screws alone do not provide sufficient strength. After being glued the joints are very strong and do not appear to show any weakness. I worried about weakening of the stringers drilling a hole for the screws, but because the screws are relatively very narrow, they have caused any problems. In another Kayak, I have lashed joints, and agree, the Netsilik Eskimo substantially lashed their kayaks, and this gave them incredible strength and flexibility. ultimately, I think it's a balance, in that lashing is the ultimate method, and glue and screw just to cut the construction time down but potentially not as strong in extreme sea conditions. Thanks and all the best with your projects. Mark