Thanks for the information LB. I had looked at pins and nails and clamps, and I have found the straight forward method of clamping in place works well and allows for errors and I have no extra holes to fill in.
Ian,
I got hold of some 4 X 2 strips and then got them cut down to 2 X 2 and trimmed so that they were as straight as anyone could ask for. Then secured them to the sides and cut sections for the ends and along the middle so that there is a cross support beam every 2 feet. So the build board should remain flat for this build at least.
Op over and I am black and blue with bruises and wish the pain would go away. But the days are getting better and back on the planking again. Have completed one side up to the water line and now working on the other side. She really is taking shape and looks good. Post photos when she is planked to the water line.