I made mine out of double layers of 3/4" CDX plywood, and rarely had trouble with splitting. I disassembled it between boats for storage, and ripped about a half inch off each piece before reassembly to clean up the edge.

: Most are made out of solid wood. I made mine out of two laminations
: of 1/2" ACX plywood. I overlapped the 8' long pieces by 2
: feet. It's really like the gunwales of a SOF and makes a very
: rigid frame. I use coarse drywall screws to attach forms to the
: strongback and, yeah, you have to be careful about splitting the
: plywood. I've built a number of boats on that strongback from
: 19' strippers to 8' SOF's for my daughters. It's getting tired.
: For the next one, I'll either use solid wood or maybe edge the
: plywood with a solid-wood strip to screw the forms to.

: =D