Strip Built Runner Plank, part ll

There’s less guess work in setting up the second half. I used the first part (the bottom) along with the old plank flipped over to establish the shape. A shim or a shingle here and there brought the two halves to a very nice fit, allowing for the bottom’s slight springback. Then the planking proceeds pretty much as before. I decided to use staples this time as the fir was a bit too hard for easy nailing. Staples are much harder to pull than nails, though, even with stapling through a piece of rope which, when you yank on it, theoretically helps get the staple started.

The other downside with the string & staple system is that I couldn’t add the centerline stringer at the same time. But the staples all came out, the stringer and the blocking at the ends for the chocks went in, and the sharp plane worked it’s magic.

The bottom can be seen on the bench at the left. The two halves fit beautifully, and there was no struggle in gluing them together. Like all runner plank laminations, it’s a clamp intensive job.

Because of the large radius, fairing was very easy once the gobs of glue were knocked back. The big shock was how stiff and light it is. After fairing it weighs 59#. And it feels great in the hand with the thin edge. Lifting a thick plank of the same weight takes a bit more finger power. I had expected to add some uni directional glass to the top and bottom to gain stiffness, and It still might need it, but preliminary flexing shows it’s just a bit more flexible than the old one. I have yet to set the boat on it, but would never have imagined it being so close. In the photo below, the little section on top is from a Monotype plank, which was the inspiration for this project. Imagine the weight they saved by going hollow! The plank still needs blocking on the bottom for the chocks.

According to THINK ICE, Spring Constants for DN planks fall between about 90 and 120. Without correcting for length, skeeter planks have a much lower number. They need to travel further to get to flat because of their higher crown. So we can’t really compare planks of different lengths using the Spring Constant of weight divided by deflection (in inches). We need a math pro to find some sort of cosign or something to level the playing field. But I did discover something interesting about crown to length ratios: every plank I checked, all of varying lengths, fell between .3 and .37. The new plank and my DN plank are both .37. What does this mean? Beats me, but it’s fun trying to figure it out. If anyone has a nice Renegade plank, I’d love to know what its deflection, weight and length/crown ratio is.

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