: I am building the 2 X 4 internal box beam. I count 10, 1 ft spaces
: between the forms of the 2 X 4 strongback. One is really 11 1/2
: inches, but I rounded up. If I count the tapered sections that
: are inserted into the strongback, then it would be an additional
: 2 ft for a total of 12 ft. I want to make sure I make the
: rectangular box beam long enough. I know that section is about
: 10 ft, but I want to know if it should be a smidgen longer to
: account for the width of a form and possibly a little more to
: make sure they do not fall off the box beam easily.

The dimension that matters is the 12' length. The length of the tapers may vary.

If you look at the forms you can get a good idea of how much taper is needed based on how close the edges of the forms are to the strongback hole. You should not need a full taper on each end, but the bow will require a longer taper than the stern.