Wizbang, I'm in the same boat as you (no pun intended). I also received a Flying Fish model for Christmas and find the plans to be rather vague in places - which is compounded by the fact that I've never put anything like this together. I got the bulkheads, keel and stern pieces together but found the waterway and planksheer to be a real problem - probably the first of many. I ended up ripping out the first waterway/planksheer pieces that I installed in that they did not properly encompass the bow timberheads and failed to overlap the hull by the requisite 3/32". My second attempt at the waterway has gone somewhat better.
What I did was tape a piece of vellum to the plan view on sheet 2-2. Taking special care to make sure I was copying the correct lines this time (the outboard dashed lines) I traced them with a French curve, cut out the velum pattern, contact cemented the pattern to a sheet of 3/8" basswood and cut out the waterway on a jig saw. It came out perfect this time around. Before I made the pattern I carefully traced the exact lines I wanted right on the plan itself and laid the velum over them. Please note that I didn't find anything in the kit that was wide enough to lay out the waterway on and had to go to a hobby shop for the basswood I needed.
I attempted Frankie's method, but the irregularities of the flying fish hull and deck precluded getting an accurate copy of the hull outline. This method would probably work great for a boat with a flatter deck.
I still have a lot of damage repair to do after my first disastrous attempt at the waterway, as I had already cemented the planksheer to the waterway and ended up destroying the planksheer when I tried to salvage it. I also broke off the stanchions on the forward bulkheads but this may turn out to my advantage as I can lay the new waterway right over the forward stanchions and can now easily mark their locations and depth. The stanchions are easy enough to glue back after I get the waterway done. Now I have to figure out how to accurately make a new planksheer.
Good luck with your project and if anyone has a way to replicate the kit provided planksheer please let me know.
Thanks, John Regan