+1 re. your strongback (whatever material) not likely being perfectly straight, so your best bet is to float the forms at least slightly so they can be aligned precisely. If you take this approach, you don't need to worry about the strongback being perfectly straight - it just needs to be stiff and strong. Plywood works just fine.

re. the issue of long term warping, keep in mind that once you get a half dozen or so strips stapled onto the forms, the entire assembly will be seriously stiff and is very unlikely to warp significantly. Warping problems usually arise after the hull or deck is removed from the forms, so strongback design is not usually the culprit.

I would try to avoid storing either hull or deck off the forms for a long time. In any case, whenever either the hull or deck is stored off the forms, it is safest to use spacer sticks which freeze the width of the shell at each form location, and ensure that the shell is supported gently.

Good luck with your project,

Best regards,

Allan Edie

: Hey guys, I'm going to start building a Laughing Loon stripper in a
: few weeks and I want to know what you think of an aluminum
: tubing strongback. I know a lot of people will be like "no
: way!" but I work on oil rigs around the world and am gone
: for a month at a time with a month off. In the time I am gone, I
: don't want the boat to warp or twist with humidity and
: temperature and all that since I live in coastal SC, and with
: how long it's going to take (hopefully done by August?), I don't
: want to risk anything. I'm building a Georgian Bay with a LOA of
: 16' 6"...about how long should the extrusion be?

: Thank you