Second Bottom Layer
Check out the foamy mess I made glueing down the second bottom layer
I had spent quiet a while contemplating on how to glue down the second bottom skin. Glueing large pretty much flat surfaces presents a lot of difficulties. Applying even pressure, spreading and applying glue quickly and evenly, not trapping any air. I thought about using epoxy or PU- foam glue and even applying the pressure with a vacuum bag. In the end I chose to use screws and Polyurethane glue.
I cut the bottom part out of three pieces and made sure to overlap the butt joints of the first layer. To help with alignment I cut a 45° chamfer on the center piece which then allowed me to slide in the joining pieces. This also helped with applying even pressure along this joint. I started with the center piece, then the bow, and then the aft piece.
Before the boards went on, I filled all the screw holes on the hull. All the screws except some on the bow remained in the boat. Also because I thought that alignment would be easy, I beveled the edges almost flush before starting the glue. I drilled and sunk all the holes like always, this time choosing to do a 20cm spacing with large screws going into the framework and 3.5x16mm screws going into the bottom plate. To release some the pressure of the PU-foam glue, and also to let out any remaining air, I drilled 2.5mm holes in between the screws.
To the he actual glue-up. In the manual of the polyurethane glue, it stated that two pieces had to be joined together within 60 minutes. In reality, this meant that each piece had to be glued and screwed within about 40minutes. Application was easy... pour it out then spread with a spatula but the glue also reacted quickly and started to foam up after about 30 min, which meant that we needed to finish screwing it down fast otherwise it would be almost impossible to get the plate fully set.
I had done some test glues on scrap and then also on the daggerboards so with the help of my friend we were able to complete the task in three sessions and barely within the timeframe of the glue starting to foam up.
Next time I would definitely put down some cover on the sides to eliminate some of the clean up. Also I felt that the whole thing had to be quiet rushed and if I were to do it again, I might actually use epoxy just to allow for some more time. (given the appropriate hardener) Of curse this would also mean that even more care would have to be taken to make sure that no air gets trapped.
What a mess!