Dreaded short thwart problem on Bounty Launch kit

[PAnderson]

It's too late for me now but I hope I caught this soon enough to help others. I am building this kit now and discovered the possible reason this is happening. I added the frames to the mold and did all of the other work. I popped the hull off of the mold and measured the width of the hull and compared it to the plans. Almost 133 MM on the plans (frames 8 & 9) and I measured 132.8 MM on my hull. Cool, I am not going to have the problem that I have been reading about with the short thwarts.

 

NOT TO BE!!! After I fit the tween frames, letting them dry, gluing them, I thought all was well. After I removed the clamps I measured again across the hull. Lo and behold, the hull had spread almost 4 MM. Like I said, too late for me now. But at least I now know and have a chance to remedy this properly as I proceed. Not sure how to do this though.

 

For future builders, I think over bending the tween frames to take out the stress and having them fit in a more relaxed manner is the solution to this problem. I hope this helps someone in the future.

 

Paul

[Keith_W]

Paul, I think that once the model is popped off the building jig, it "wants" to spread out. I solved my problem by squeezing the hull together and installing the thwarts. As they went on one by one, they held the hull in shape.

[PAnderson]

Thanks Keith. I checked my hull before and after Popping it off the hull. No measurable spring. I don't know about others but mine sprung from the tween frames. Makes sense too. Bending them to the hull, they still have a lot of residual stress built up. It's good to know that the thwarts will hold the shape. Did the sheer clamp and the thwart riser make it more difficult to squeeze the hull back into shape?

 

Paul

[Keith_W]

There was no problem squeezing the hull back into shape, Paul. A pair of strong clamps took care of that I installed the thwarts, then cranked the clamps until it all came together.

[Cathead]

I agree, with my kit I just compressed the hull back to the original/intended with and glued in the thwarts and such. Didn't cause any issue.

[Cathead]

Posted this on your build log, but figured I'd share it here too if anyone else wonders the same question: 

 

Based on my experience, go straight at it with carpentry clamps:

 

 

This issue scared me, too, until various nice folks on my log assured me that it was a common quirk and quite fixable. So I just tackled it head on and hoped for the best. I found that when the thwarts are glued in, they're enough to hold the hull in place without spreading, which made installing the gunwales easy as the hull was now stable and the proper shape.