Nifty, and portable too. Is that an Endeavour in the nude?

: Hello All: Just posting a slightly different strongback approach. I really
: did like the steel (and aluminum) square tube variations posted recently,
: but as comfortable as I am working with steel, my problem is that I needed
: a mobile strongback, and therefore it had to be extremely rigid both in
: bending and in torsion. I have a pretty extensive shop, but alas, too
: crowded for kayak construction. So I must share a garage workspace with my
: wife's car. So you married guys will appreciate the priorities here.

: The boxbeam itself is 16ft long x 8" x 9". The whole affair can be
: made from two sheets of 1/2" ply (although the one shown is made from
: one sheet of 1/2" CDX, and some misc other stuff on hand.) One of the
: tricks in box beam construction is to have well fitting blocking inside,
: (in the one shown, there are five blocks) one at each joint and each end.
: And it must have four sides. Before I put on the fourth side I was able to
: twist the beam quite easily.

: To test how rigid when completed, I hung two 100 pound buckets of scrap metal
: from the ends of two pipe clamps approx two feet from the center of the
: beam and opposing each other at opposite ends of the beam, and I was
: unable to detect any measurable twist with a fairly precise level. So
: testing it successfully with approx 400 ft/lbs of applied torsion I felt
: fairly safe in mounting casters and rolling along.

: Happy trails
: ron