Kevin is dry-fitting this layer from the bow, toward the stern. In the bow the pieces are approx. 300mm (12") wide, which has worked well. Further aft the twist reduces rapidly so wider pieces can be fitted without problem.
|Second layer of 9mm bottom skin being dry-fitted.|
To further complicate it, this boat has a broken sheer, meaning that there is a hard break in the side profile instead of having smooth curves that flow from one end of the boat to the other. That means that the sheer must be done in two sections. The aft flat part of the sheer clamp is done first, then the forward curved part is built off the aft section.
Kevin laminated the aft section of the sheer clamp during the week, ahead of me arriving to help with the more complicated forward section.
|This photo shows the twist that is formed in the aft part of the sheer clamp as it changes from tumblehome at the transom to the beginnings of flare at the break in the sheer.|
The Stem is more complicated. The angle of the bevel for the skin must be marked and cut first in the area where the sheer clamp will fit. This angle can be established by running a batten across the forward 3 or 4 frames to check that it contacts all of them correctly and lies flat against the bevel on the stem. Once that stem bevel angle is correct the rebate to receive the sheer clamp can be formed.
|A slightly different perspective of the intersection.|
The sheer clamp must also be prepared with its ends trimmed to properly meet the aft sheer clamp and the stem. The aft end is relatively simple, with an angle in only one direction that is easy to mark, rough-cut with a saw, then fine-tune with a sharp plane.
|The junction of the two sheer clamps at the sheer break. The cut angle for a good fit is quite easy to work out.|
The forward end is more complicated so it is best to first work out the cut angles (which run in two directions so that the bevel is not parallel to any of the surfaces of the timber) on a length of off-cut of identical size to the sheer clamp. Cut this off-cut and fine-tune to a perfect fit, then transfer the angles to the sheer clamp on the workbench, where they can be accurately drawn, cut and planed. Test fit on the boat.
Now comes the part that demands ingenuity, to deal with the enormous amount of twist in the bow sections. We were working with very nice clear Douglas fir, which is stiff and not keen to twist as we needed. It didn't work to rely on clamps alone to do this work, the timber came in most of the way but still needed about 20 degrees of twist. We set up a Spanish windlass to do all of the work of pulling the timber in against the stem so that the clamps would only have to work on the twist.
|This was our setup for the dry-fitting phase of the first layer of the sheer clamp.|
We were not confident of being able to pull it in totally with slippery glue complicating the work, so we decided to leave it clamped for two days to set in some of the bend. When we returned to it the pre-set of the timber made it easier to pull it back in. Again, we used a Spanish windlass to apply the bending forces. We used a different clamp setup to do the twisting, with the handles of the clamps lashed together to apply the twisting force.
We were working with timber thickness to laminate the sheer clamps in three pieces. Doing it in four thinner strips will make it easier to pull to shape.
The next step will be to laminate the other two layers onto the sheer clamp, which should be completed in the next few days.