Might just be my own invention…. Had abysmal luck trying to post pics here, maybe I can explain how this works.

Pipe clamps are great for forcing two objects together. There have been times when I’ve needed to force two objects apart a bit, which can be done with a stick long enough to move the objects into position but it needs to be thick enough to stand up to the strain. without bending.

Using a pipe clamp for this requires a second piece of pipe, long enough to span the gap between objects and a little more for the clamp end itself to ride upon. A much shorter pipe is needed on which the screw-powered end will ride. Both pipes, having tapered ‘pipe threads’, usually can be screwed into the screw-bearing end of the clamp, with their threaded ends in contact with one another.

So you now place the clamp with both faces in contact with the objects you want to force apart, then turn the screw on the adjustable end to push it way from its fixed mate.

This is capable of moving flexible things apart an inch, maybe more, when they’re at least as far apart as those clamp ends can be when the screw’s backed off fully, maybe a minimum of five or six inches. I use 1/2” pipe clamps so the pipes I use usually aren’t longer than 6’ or they’ll flex too much. 3/4” clamps, using stiffer pipe, may be more capable at greater widths.

Or you can use a 2x4 cut a bit short of the distance between your two objects then use paired wedges as a jack to move things where you want ‘em to end up. Reversed pipe clamp can be used single-handed (the clamp rests on those two pipes) where a 2x4 usually needs a third hand to hold the stationary end in place while the other two force the wedges against one another to provide the motive power to move those objects.

A normal pipe clamp is a couple of pieces of hardware that move along a pipe. The hardware is set to apply compression inward. If you reverse the pieces (may not be possible on all brands) it pushes outward. Putting that between the sheers at the center thwart will force the sides of the boat apart removing the compression force that is bending the frame out of shape. At that time, you can add the stiffeners and when you release the pipe clamp the frame should hold its shape.

If the stiffeners are stiff enough and properly installed, they can also force the frame back into the correct shape, even without the pipe clamp, as long as the hull is still flexible.

Laszlo

Thank you spclark and Laszlo, I now understand what you were suggesting. I've now got a few ideas to try, and should be able to get the centerboard box installed.

I finally got a chance to experiment with some of the ideas proposed, (my work site is two hours from my home).

I clamped a 2x2 strip of lumber to the middle frame, and that straightened the frame to the point that the centerboard box fit well. So I'm sure that attaching that piece permanently will do the trick.

Now a separate problem is that, because the boat appears to be slightly too narrow, the seat doesn't fit quite right. But it looks like sanding the slots on either side of that piece of wood will get me there.

Glad to hear that it all worked out for you with the frame. I always consider seat patterns a serving suggestion. I've never had a seat fit the first time without some tweaking. There's just too much natural variation in how wood bends.

Laszlo