I think I figured out why the hull expanded:
1. Weather. There were big fluctuations in temperature/humidity when I was ready to glass the hull. I was too intent on Getting It Done, and didn't notice the expansion.
2. Short kayak, lots of small strips, and new-to-me wood. I think that the low-density pawlonia absorbs/desorbs moisture quickly. The ease of heat-bending is a clue.
3. Timing. I'll have to, in the future, find a way to put the halves together while everything is still fair. I may try glassing the hull exterior first in the future.
I went on that Favorite Message Board for suggestions, and as expected, plenty of response. This is one of the suggestions:
Ratchet straps and blocks of wood pulling the hull back into the forms. Fortunately inexpensive, $10/4. Very glad to see that when the gunwale is pulled in, the hull conforms almost perfectly to the shape of the forms.
Of course, now that both sides are glassed, the wood won't react to temperature/humidity changes, but I hope that the whole thing "takes a set" while the epoxy continues to cure for a while.
Nope. 😒 I left the above arrangement in place while I glassed the deck underside. When I removed the forms, the hull sprang right back out to its original shape.
I tried getting the deck to fit by using the straps and blocks of wood, but the hull was very much wider than the deck, and the deck kept diving down into the hull. On to Plan B:
I put the forms back in with the straps holding them in place as in the above photo. I made these sticks of lumber to pull the hull back into the forms. After I got over cringing about drilling holes through the hull, I did several of these. I'm hoping that they will hold the hull in shape enough to be able to work with the straps & blocks.
As usual, sanding the hull was more work than expected, and every flaw is staring at me. 😉
Interesting: I did set the hull up with several forms hot-melt glued in place. They fit snugly. While sanding, they had a tendency to fall out, and today I noticed that they don't fit snugly any more-the gunwales have expanded back out to where they were before I glassed the interior. The epoxy shrinkage is temporary? I'm interested in seeing if the hull shrinks back to the forms after glassing. The hull now sticks out as much as 1" from the forms, and that will make the fit "challenging".
After setting the glass in place, I only needed to cut one small dart in the end of the stern. I decided on two 3' x 2" reinforcing strips at the bow & stern.
The strip in place. I find it easier to place the strip on the wet epoxy, after the main sheath of glass is saturated, than to try & saturate the two layers at once.
After the first fill coat, I noticed that the hull is definitely not shrinking back to the forms-on the contrary, it spread out. On my favorite message board, one guy suggested that it was more about the wood being affected by temperature and humidity than about epoxy shrinkage. It's going to take some "serious doing" to fix this. Come to think of it, this is the same problem that I had last year. Maybe 3/16" strips aren't really a good idea?
Almost ironically, this is the best epoxy coating I've ever done on a hull. I went for a thicker fill coat, and the weave is mostly filled after the first coat.
After removing the deck, once again, the Bow and Stern forms wouldn't come off the hull-just like the last time I built a strongback without internal stems. Again, I had to "get medieval" to remove them. Oddly, I didn't really find any spots where the forms & hull were glued together badly, but I guess it doesn't take much. The wood glue on the duct tape seems to stick just enough to make it difficult.
I filleted the ends. In the past. I had left these wet, and put the fiberglass on the wet putty. This time, I'm going to let them dry, sand, and possibly use some more before fiberglassing.
I did sand the fillet basically, and skim on another coating of dookie. I placed form #3 back in the hull, by way of experiment to see if I can use the forms on wet fiberglass to prevent shrinkage. Form #5 is in the dry area.
I decide not to go "nuts" fairing the interior of the hull this time. If the glue residue is so tough, and so resistant to everything, some of it can stay in.
After 'glassing the interior, I placed three forms in the hull, and noticed that the sheer of the hull was actually wider than the forms. The forms are (supposed to be) there to prevent the hull from shrinking too narrow, but there was a gap between the forms and the hull. I decided to tape them together & see what happens. This might have been the problem last year.
The usual end caps. I kept them as small as possible.
The skeg box in place. This turned out to be a bit of a finagle, because the center strip is covered in dookie, and I couldn't see it for alignment. I got around it by marking the center with two small holes.
I'm also trying to pull the gunwales together with tape while the epoxy (supposedly?) shrinks. I placed a few forms in the hull, pulled the hull to them, and placed tape across the boat. I'm going to try this with hot-melt glue when I 'glass the hull exterior.
Interesting. After the third coat of epoxy cured overnight, the pieces of tape that were tight became slack. It seems that the epoxy takes a day or three to shrink. I'm definitely putting several forms in the hull while I 'glass the exterior.
