If it is more than 13ft, then it should be called the F13. I would be fine with that. I do see the point of saving on wood, but if you have any curves it will be longer than 1.5 sheets of ply (at least in the usa, I am not sure of metric sheet sizes). Plus the scarf takes a good 6-8 inches out, so it does not seem to me we will save much wood.