It's not as critical as you might suspect. Much different from building airplanes. A straight grain 2x4 works fine, as long as you give it several days to stabilize to the temp and humidity of your shop before you line up the forms. It doesn't matter if there's a little wow in it. Put a screw in the middle of each end, stretch a string, and spray it with paint. Do the same thing on the side, and the unpainted stripes will be dead on. Line up your forms with the stripes, not with the 2x4.

One other thing. You may have to do some wood butchery at the ends when it's time to separate the halves. I had to whack 2 feet off each end, and was glad it was a cheap 2x4 and not a carefully constructed box beam. The strongback was too short to reuse, so I carved a Greenland paddle out of it.

> Just getting started on a boat and already couild use some advice -
> Anybody have any great solutions for building/buying a box beam? I
> searched the archives but came up empty. I know that some recommend an
> aluminum beam, but I don't know where to find one and I suspect it is more
> unforgiving (when lining up forms) than a wooden equivalent.

> I've seen a box beam kit advertised for sale, but as it is made from
> plywood (I assume) and would be shipped from about 3500 miles from where I
> live I think I'd just as soon make my own. I'm not too interested in
> taking a chance on a clear piece of 2x4. Has anyone tried several 1x4
> pieces of pressboard laminated together?

> Any thoughts much appreciated.