In order to prevent another Crooked Kayak Disaster, I looked for a new way to set up a strongback. Rob Macks uses what he calls an "external box beam" for a strongback, so I bought his kayak building plans to get the dimensions & instructions.
I made it 19' long-two 8' sections, one 3' section, and two "nesting sections" in between. Its so long, I couldn't fit it all in the picture. Rob calls for 1/2" CDX plywood. I almost used "nicey-nice" 3/4" ply, and I'm glad I didn't, because it weighs a lot as it is. I like the idea of the beam being longer than the whole kayak, because now I can align everything to a string, and not have to resort to shenanigans to get the end forms aligned. It was harder to build than I thought it would be-I had to re-do a section to get it to fit together. Here, I'm using a variety of shims to level it on my uneven basement floor.