I am now building my third SOF boat and have been experimenting. I don't like using screws in the stringers where there is risk that the weakening caused by the drilled hole might lead to a break. Only at the ends to fasten them to the stems. To hold stringers in place temporarily on the ply frames (Yost-style SOF) I use cable ties with a small gun that grabs the end and tightens it as you click on the trigger and then cuts the end when sufficient tension is applied. Most joints don't even need this as they are under compression as the stringer curves around the frames. To permanently keep the stringers in place I use a thick viscous MS-polymer construction glue, (X-Tack 7 or Essve ESS TACK PRO1 High-viscosity 1-component Contact Adhesive with direct load carrying capability in Europe, and there are many others) in the joint and around it as a fillet. This glue comes in cartridge and needs a special strong gun with a low-geared trigger as it is very viscous. The fillets are very quick to make with a gloved finger wet with a small amount of mineral spirits as it seems to be soluble in that. It hardens to a soft rubbery consistency and the hardening on the surface starts after about 5 minutes but max strength takes about 24 hours. I like the slight flexibility of this glued joint in a SOF boat. If I make a mistake, the glue can be removed with a chisel or sharp knife and lumps and smears can be removed with a sharp scraper or chisel. It can be painted. To join the stringers to the stem pieces I use a lashing to pull the stringer in and also use the glue, and add a stainless steel decking screw if I think it is necessary, drilling a hole in the stringer and countersinking the screw so the stringer doesn't split. Decking screws have a coarse thread that I think holds better in plywood than a standard screw.I would not use MS-polymer glue for joints requiring maximum strength and stiffness, i.e., the leeboard attachment of a sailing canoe. For these I am using thickened epoxy.
Peter