Modified Sheldrake Cardboard Core
Start: July 7, 2014.
Finish: n/a
This is the 3rd board I’ve built. 2nd hollow, cardboard core. This is a prototype model; I’m still developing my process.
I use a Sheldrake template and I modified the plans to remove much of the horizontal stringers. On my first board, I just cut them to size or disregarded them, after I had assembled the board. This left the “holes” that the stringers would have filled. It worked OK, but there’s noticeable weakness, bending and separation in places. I removed the slots that the stringers would slide into. I expected to leave stringer near the rail, but it ended up affecting the artistic quality of the board, so I removed them without recutting the pieces (and repainting). I had some issues glassing it and I used too much force testing a mock-up “vaccum bag” using shrink wrap. I’ll modify the plans for future builds. Despite some folks’ intuition, the lengthwise stringers are unnecessary. The board would wobble and be difficult to work with without them, However one (or two, for symmetry) that only connects two cross pieces is enough to lock the whole thing in place. I keep them in the tail area to add a little extra strength for the fins and leash. People hardly notice it. They see diamonds instead of hexagons. This approach gives me greater artistic liberty as well. I edited the drawings using Corel. Unfortunately, I haven’t been able to find a satisfactory way to edit the drawings using free/open-source software. One other benefit to this approach is that the required sheets of cardboard reduce by 7 (to 11 from 19). I had the drawings cut on a laser cutter the engraver at my work uses on cardboard I acquired from the rubbish. I wanted to get the lengthwise rail pieces cut in two single pieces on a cnc at work, but they said it can’t handle such a small bit for the design (they mostly cut relatively simple cabinetry).
My primary goals with this board, beside strength, is transparency. On my first board, I tried to create a highly transparent shell, then adhere that to the core. It didn’t really work too well. On this board, I had an idea to try to use woven roving on the cardboard to get a better bond. There’s a possibility, if done right, this approach could work, but my experience was that the woven roving held it’s (cylindrical) form too well and didn’t seem to want to stick to the cardboard. When I sat the shell on it, the roving stuck strong to the shell and hardly to the cardboard, so I coudln’t really move the shell around to align things. It produced an uglier result than desired, but the board is still blowing minds. On a future board, I plan to skip the roving. I plan to rough sand the cardboard edge, close to 2mm deep. I don’t think the shrink wrap helped much, either. Better to use weight.
Without the lengthwise stringers, until the board is glassed, it is highly flexible along the rocker. In order to work with this, I designed a custom support (out of cardboard) that has a vertical piece every 8cm from front to back. I left some out of the center, which made for a minor flaw. Also, I left the closest vertical piece to the tail 16cm away and 8cm from the nose. This caused some minor sag, but I don’t think it will affect the board’s performance much. Mostly an aesthetic issue. I had the support stay about 6cm away from the rail edge so as not to cause a problem with wrapping the rails. I’ve found a solution to this and I plan to have a vertical piece from from 2cm from the tail and nose then one every 5cm or so. I also plan to build one that will give the proper deck “rocker”, since it stays a little flimsy until 2 pieces of glass are on.
I use foam to give support to the fin and leash plug areas. My first board used 2-part pour marine foam. I had some issues with that, since I had already glassed the board and the pressure from the foam’s expansion caused some deformations. I was able to deal with it, though. On this board, I decided on my fin laout in advance. I chose thruster since it required less foam than a quad layout. That’s mostly because I’m working with a leash plug and even with the plug, I’m only using 2-4 less cells. I think the thruster will be good, because I think it might slow the board down a little. I used the spray foam that’s used to seal gaps you can get at a hardware store. I think the marine pour foam may be cheaper in the long run if you plan to build many, but the spray foam seems to be a good idea for a one-off board. The spray foam is far less dense than the marine foam. It’s water resistant, not -proof. I took a chance on this, since I don’t plan on keeping it exposed to water for long. Also, I figured it should provide enough support, since I see guys are managing to secure fin plugs to just the cardboard itself. I haven’t rode on it yet, but it seems plenty strong. I took a chisel to it to knock down the resin and it withstood that.
On my first board, I built the vented leash plug in being mindful more of airflow than of strength. I ultimately paid the price for that decision. I ripped the glass around the leashplug on an overhead session and a lot of water got in. I eventually glassed over the plug hole and tried to surf leashless, but there must be a pin hole somewhere I couldn’t find and I gave up on it. The board was pretty heavy, since I used a lot of resin to avoid sanding. It’s now wall art. This board’s primary testing is with the leash plug setup. I ended up reducing the amount of foam I originally planned on, since the probox could fit with 2 of the lengthwise stringers. This caused me to reduce the foam I used around the leash plug. I think my approach this time is much better than last. It seems fairly strong. I’m tempted to get it attached to a machine to actually test how much tension it’s capable of handling, but I’ll just wait to see what happens in the water. This has been the main focus on my R&D on this board. I hope I don’t have to go back to the drawing board. But, I did make this board with this in mind. If it ends up on the wall, at least i’ts beautiful.
On my first board, I used a lot of q-cell to make nice clean rails and painted the rails. I left this unpainted. Only the cardboard core is painted and the areas with foam. It’s not too bad if you have to use a few extra pieces of glass to smooth out the rail areas. It doesn’t need to be as transparent as the center.
A note on the name. I originally thought of a board called The Feather. I may make one in the future, but it lead me to think about making the board a bird, since a bird has feathers. And I thought of a board that I paint different colors so it looks different depending on which way you’re looking at it, so I wanted to try to put some kind of motion into it, so I wanted to create a diving bird. I figured I wouldn’t be able to put much detail into it and would depend mostly on the “pixels” of the cells, which was basically true, so I chose to use the contrasting colors white and black. So I have a black bird. So I started thinking about black birds. I used to have a native american raven logo sticker, so I was thinking about that, then I read a description of the raven as a creature of metamorphosis, and symbolizes change/transformation. Then there was no question what it was to be called.
I can’t wait to ride it and get some footage of it flapping its wings!
moderator’s note: pictures were posted way larger than necessary, which creates problems on some computers viewing the forum. Here are the links to the pics at the size posted.
http://www.swaylocks.com/sites/default/files/raven1.jpg
http://www.swaylocks.com/sites/default/files/raven2b.jpg
I took one, and resized it to 20% with MS Paint. It went from 2988 x 5312 pixels, to 598 x 1063 pixels. Please post pics at approx. size they will appear in the post, thanks.