Friday, June 14, 2013

The Utility, part 5: The Sheers

June is upon us, and with it my daughter's birthday, as well as the arrival of the stifling summer heat and humidity we're "blessed" with here in the south. Ah well... Every day above ground is a good day, and this day is off to a great start.

It was a beautiful, clear morning as I drove on traffic-less back roads, listening to Aaron Copeland's Third Symphony (possibly the greatest piece of American music) on the radio. Passing a faded American flag, backlit by the early morning sun, I thought of my grandfather and the hardships he endured during the 1940's... and of how, with the nightmare of the war behind him, he used to drool over 1950's Chris-Crafts at a local boat dealer. I only learned about that recently, along with the fact that he'd contemplated building his own boat.

But, I'm digressing.

The Sheers:

"You'll never have enough clamps." Start building a boat, and you're going to hear this early-on from other boatbuilders. By the time you get to installing your sheer clamps, you're going to need them. (I wonder if that's why they're called sheer "clamps"?)

Sheer clamps, also frequently referred to as "sheers," are the long boards that form the top rim of the sides of the boat. They extend from the outer corners of the transom, and meet at the stem, forming the pointed bow of the boat.

In any case, the Irwin "Quick Grip" bar clamps you'll see a lot of in my photos are great all-around clamps. They aren't perfect, however, nor are they indestructible. Although I had many 6" and 12" sizes of them by the time I was ready to install my sheers, I still needed to get larger 24" clamps of both the Quick Grip and standard bar clamp varieties. The 24" Quick Grip clamps were perfect for holding the sheers upward into position. But, this style of clamp just couldn't complete the bend of the sheers up forward. For this, the standard bar clamps do a much better job.

Sheer clamp notch in the transom frame. This shallow notch would later pose its own challenge.
A 24" Quick Grip clamp (back) holds the sheer upward into position. A 6" clamp (front) is being used as a lever to twist the sheer into the required vertical orientation.
A 24" standard bar clamp holds the forward tip of the sheer into its fully-curved position against the breasthook and stem.

The stock for the sheer clamps themselves was again Southern Yellow Pine, as with the chine logs. This was for the same reasons of the wood being both inexpensive and easy to bend. The sheers are built from two layers of 1-1/4" x 5/8" x 12' material. I ripped the 4 strips from a 12' "1x6" board from Lowe's that had fairly vertical grain. Of course, a so-called "1x6" is in reality only 3/4" thick. I planed the 4 pieces down from 3/4" to 5/8" using a small planer/jointer my dad bought from Harbor Freight. In retrospect, I probably should've planed down the board first, then ripped the 4 pieces.

Overall fitting of the sheers was easier than the chines. The bevel in the forward frame notch was milder for the sheer than was needed for the chines. Unlike the chine, which twists as it bends, the sheer is supposed to remain in a vertical orientation.

Prior to bending the sheers fully, I wrapped towels around the wood and poured boiling water on them, then let them soak a while. After doing this a couple of times over the course of a couple of hours, the sheers bent easily into place. I measured the angle at the junction of the breasthook and stem, and used this as a guide to cut the forward tip of the sheers. After some additional fitting, I clamped the sheers into place and let them sit overnight. Later, I drilled holes & screwed them into position at the breasthook, frame #2, and frame #1.

I could not determine a way to drive screws through the sheer and into the transom frame, however. This was due to the shallow nature of the transom frame's sheer notch. Rather than drive a screw through the back of the transom and into the end grain of the sheer, I decided to simply let the epoxy hold it for the time being.

The instructions state that you need to drive screws through both sheer layers & into the frames. However, I did not see a way to hold the sheer into place long enough to let the epoxy dry without driving screws into the frames. This was particularly the case because I had to force the sheers into a vertical orientation by using bar clamps as levers, as shown above.

Once the first sheer layer had been fitted, it was time to disassemble, add thickened epoxy, and re-assemble. I used System Three Gel Magic, thickened with mahogany sawdust. I attached the sheers at the breasthook and frame #2 first. Then later, after the epoxy cured at those joints, I finished the aft section.

Forward tip of starboard sheer (layer 1) attached.
Forward tip of port sheer (layer 1) attached.

After the first layer was on, I sanded it in preparation for adding the second layer. Fitting the second layer was easier, since it basically just had to lay on top of the first. This is where you need a lot of clamps!

Soaking the forward end of sheer layer #2.
Starboard sheer layer 2 bent & fitted into position.
2" silicon bronze screws were staggered between those used to attach layer #1.
Disassembled & ready for epoxy.
Waiting for the epoxy to cure. I used Glen-L Poxy Shield thickened with #2 silica and mahogany sawdust.
Et voilĂ !
Since layer 1 was screwed directly to the frames, I drove 1-1/4" silicon bronze screws through both sheer layers on either side of each frame. I hope I countersunk these adequately for fairing.
Repeat for the port side.

Both layers on & laminated!

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