Hope your lowboy has four long beams instead of two. The upright
crossmembers between the outer pairs helps keep the webs vertical after
you remove the central crossbeams for your keel slot. If the existing
crossmembers aren't channel, get some. Use medium weight 6"-8" channel
and lay it flat between the rails tight against the web as low as
they'll go. Weld them to the web only and then reinforce with vertical
quarter-inch gussets--8"x8" if possible. Don't weld anything to the
long rail flanges. That goes for your stake pockets and rope hooks as
well as the crossmembers. And like the gentlemen said, look at a
professionally built trailer. The cradling is almost trivial, once you
have the trailer.
Good luck, Boatdreams.
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Courtney Thomas wrote:
By large I mean 40' or more.

Thank you.