My plan is to get the boat out of the basement before putting on the deck plywood so it will be somewhat easier to handle and slightly lighter. But, there isnt any reason not to go ahead with doing the rough cutting and fitting. After a bit of sketching of how to cut the pieces, it seemed the only way to get the front deck pieces out of one sheet of plywood was to use the factory edge down the centerline of the boat starting about 18" in from the end. The opposite side piece would use the other side of the sheet but the sheet would be flipped over to fit the mirror image piece. I plan on having a natural wood finish on the deck using just the plywood but with a paint graphic band down the center to hind the seam. Luckily, the plywood has veneer that looks very similar in grain and color on both sides of the sheet. The first sheet of deck plywood is not supposed to stop at the dash or any frame, but continue as far as possible along the carling and sheer as not to create a weak spot. After positioning the full sheet down the centerline of the boat and clamping it in place, a line was traced on the underneath side to show where to cut it. A 1/4" thick scrap piece was used to offset the pencil mark to allow at least a 1/4" overhang at all edges. 
Then the sheet was taken off the boat and set up in my shop for cutting with a jig saw. I quit for the day at that point to sleep on it before cutting.
Then the sheet was taken off the boat and set up in my shop for cutting with a jig saw. I quit for the day at that point to sleep on it before cutting. Some blue tape was put beside the cut line which minimized any tear out of the veneer and helped visualize the line to be cut. The firse piece went well as did the second. Putting them both on the boat confirmed that the color and grain look very similar between the two halves.
The next task was the back halves. The first one was marked and was left overnight just in case there was something I was overlooking. Nope, cut it and it fit. Tried it on the other side and it fit there too. So I used it as a pattern for the other side. 
I left overlaps between the front and back pieces to give me some adjustment when finally glued and attached.
I left overlaps between the front and back pieces to give me some adjustment when finally glued and attached.
The sides of the middle frame were unsupported and could easily be pushed out of plumb so I added a temporary cross beam and some angle braces from it to the form to stablize them. Now they can be worked on without moving around.
