First, I had to level the boat in fore and aft and athwartships directions. I cut my supports to keep the waterline rather than the gunwale line level, so I had to shim up the aft support. First, to establish the exact position of the gunwale line at the beam bulkheads, I cut holes in the hull at those positions, as much energy was put in to achieve exact positioning of the beam bulkheads and thus their gunwale mark would be the best points to use in my boat.
Then, using extensions out trough these openings and a standard leveller inside to control athwartship alignment, I used a laser leveller to establish exact fore and aft alignment. Packed up as requires as shown in the next picture. Then I used a cardboard full size template for the cutout that I made from measures in the plan book, had a single light source several meters away and in combination with the laser leveller transferred the shape to the hull. I used my oscillating saw to make small cuts each side of the bulkhead to control position of the pattern. Then cut.