I decided to go with simple L shaped brackets to help me get the sheer strakes into place. Two minutes with a hand saw and some scrap ply and I had 10 L shaped pieces.
Once they were clamped in place, it gave the sheers something to rest on while I clamped it all up. You can see these more clearly in the second picture.
Now that they are steamed into place, and with the help of towels, boiling water, clamps and a truckers hitch, I am twisting them a little to follow the line of the frames. To avoid the clamps damaging the sheer strakes, I clamped a cutoff either side and then twisted. With the leverage of the long bar clamps, and the 3:1 advantage of the truckers hitch (poor mans pulley) you do have to go slowly and carefully to avoid that snapping sound. I hate that snapping sound.
It's really starting to look like a boat now. I can see the shape of it.
I need to bevel each of the notches and then glue and screw. I have a Bosch PMF 180 (Fein multimaster clone) and it happily cuts oak. I suspect this will be easier than trying to lie under the frame and hit a chisel upwards.