Warped Centerboard Case

[Donm1753]

I finally got to start on my Pocketship over the weekend. I am building from a kit and the first thing I noticed is that most of the 9mm plywood is warped. After cutting out the two centerboard case sides, I found there was about 1/4" bow in both pieces from the leading edge to the trailing edge. To make matters worse, both sides are laid out in the same direction, so they both warp in the same direction rather than opposite of each other. I weighted the ends for about 24 hours and by the time I was ready to start fiberglassing most of the warp seemed to have worked itself out. Unfortunately, by the time I was done fiberglassing the warp had returned. I estimate it is now about a 3/8" bow with the fiberglass at a green cure stage. Has anyone else had this trouble? If so, I would like to know what was done to correct the situation. At this point I am considering laminating a horizontal rib the length of the centerboard case to the outside of the centerboard case on both sides just above the level of the floors. The rib would be 1 1/2 wide and 1 1/2 " high where it is glued to the centerboard case. The top surface would be tapered to 3/4" high on the outside edge. This would form a bevel between the floorboards and the centerboard case. I am hoping a single rib on each side will straighten out the panels and not cause the panels to twist instead. If anybody has any alternative ideas I would love to hear them. Thanks in advance.

Don Maurer

Brownsburg, IN

[Donm1753]

I had a chance to clamp a rib to the centerboard sides to see if it would eliminate the warp. It took out most of the warp but there are still several "waves" along the bottom edge about 3/32" deep. Depending on how these fall along the two sides will determine whether there will be interference with the centerboard or not. There is probably no way to tell for sure without building both the centerboard case and the centerboard and doing a test fit.

[ahamm]

I've had no warping with any of my ply and it was unloaded in the rain from the UPS truck. Have you talked to the peeps at CLC they might replace it.
Remember the lower 6 inches or so of the centerboard trunk is incorporated in the keelson and is clamped and braced during the glue-up, that may cure the edge warp.
Have any pictures ?
Allen

[Donm1753]

I have the sides laying on concrete concave side down to equalize the moisture content for a couple of days now, as John suggested in an email. They don't appear to have flattened any, but one side is fiberglassed. The rest of the plywood has been unstacked and on edge. It has been aclimating in an unheated garage for about 3 weeks now and it is still as warped and wavy as ever. I'm talking about the 9 mm only. The 6 mm seems ok. I am going to assemble the centerboard case with screws this weekend to see how bad the warping is. If it looks like I am going to have interference with the centerboard I will cut a new case side laid out so the two sides curve away from each other. With the sides curving away from each other I think the internal spacers and the keel sides will help pull it back in some without introducing warp to the keel. How do you post photos?

[ahamm]

I don't think there is a way to post pictures directly to the forum.
Most of us use a third party service like Pica or Flickr , My build pictures are at
http://www.flickr.com/photos/ah46/

[Donm1753]

Saturday was a nice sunny day after having rained the night before, so I took all of my 9mm plywood and laid it out on the driveway concave side down all day. When I looked at it that evening much of the warp had straightened out. Unfortunately it had all returned by the next morning. I cut and planed the spacers to the correct thickness and screwed together the centerboard case using the two warped previously fiberglassed trunk panels. I tried inserting the centerboard halves (no fiberglass yet). It was a friction tight fit. It would still move, but it would never drop on its own, especially once it was glassed. So I spent most of Sunday cutting and glassing a new centerboard case panel. This one is laid out so it bows outward. So the centerboard case will be the correct thickness on the two ends and the keelson will pull it in line along the bottom. At worst there will be a slight bow in the midsection where hopefully it will not matter.