Q: How do you get 121 mm out of 70 mm?
A: You don't!!
Yet, I am now led to believe that it is possible since it is on the plans.
This is related to beam trough 6 and the aft deck area. On the plans, Wharram calls for a 121mm camber in the deck support that attaches to the aft side of the beam trough. Yet, he specifies a piece of 70mmx20mm piece of lumber to do it with.
Remember, Wharram references from strange data points - this measurement is interpolated from the plan drawing of the #6 beam trough where the initial measurement is first referenced from the top of the upper stringer notch, up 80mm to the top edge of the camber in the center. The actual bottom of the deck support piece is shown to lie in parallel to the bottom of the top stringer.
When you attach the deck support piece to the beam trough according the the plans, then measure up to the top center reference point for the camber, the total measurement is 121mm. He specifies in the book to use a 70mm (high) x 20mm (thick) piece of lumber to accomplish this feat of Wharramness.
I understand that the piece is actually split by the plywood beam support bolt brace, and that one could use a 70mm piece of lumber, pre cut, then attached at an angle to accomplish this support. However, that is not what the plans show.
How did you solve this problem?