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December 2009

Using SCUBA For Kayak Rolling Practice

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I met a sea kayaker today at Deception Pass who had designed and constructed a scuba system for kayaking. He put a small air tank in the day hatch compartment of his Chatham 16, secured it with inflatable bags so it wouldn't roll around, and ran an air hose out of a a custom hatch cover to amouth piece held under the bungees on the deck. With this apparatus he could stay underwater a very long time. He made it to help his rolling practice, so he could take his time, concentrate on technique and not have to worry about coming up for air.  

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When learning to roll I think it's important to remove all distractions so you can concentrate on technique.  I recommend practicing in warm pool with a dive mask, so that you are comfortable and can see clearly underwater, and don't have water running in your nose. The scuba adds the additional comfort of not having to worry about breathing.

Another trick I've heard about is to use a snorkel connected to a tube that runs down your sprayskirt into the cockpit. While capsized you can breathe the air inside the cockpit. Exhaled carbon dioxide will build up in the circuit, the amount depending on the length and diameter of the tubing. So if you are under a long time, you might find yourself having to breathe deeper to achieve adequate gas exchange. I've never tried it so I can't say much more about it. For paddlers who are just learning to roll it's probably too much to deal with. Try it at your own risk.

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UPDATE: Warren Williamson's Custom Stitch and Glue Greenland Kayak

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I dropped by Warren Williamson's workshop the other day and he showed me the progress he has made on his custom stitch and glue Greenland kayak. The panels have been joined together -- spot welded with thickened epoxy, but no fillets or fiberglass yet. The panels came together easily to form a beautiful, sleek and lightweight symmetric hull.

Some building notes:

Since the hull panels were cut with a CNC router from 8x4 sections of plywood, they had to be joined together using butt joints and "butt blocks". Using a butt joint is much easier than trying to scarf together thin plywood panels. Warren was a little concerned about getting the joint right, because a small error in lining the panels up at the joint will be magnified at the ends.  So he basically lofted the panel out full scale and laid the panels out on the diagram before joining them together. If you look very carefully along the length of the hull you can see flat spots where the joints are. Warren said that using smaller butt blocks might have avoided this. One could also try using a few sheets of fiberglass instead, which apparently what Pygmy does.

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For stitching the hull together, he used two external forms, internal building forms and four permanent bulkheads. There is a small bulkhead at both the bow and the stern, which help give the hull a concave shape at the ends. This will produce a small air chamber at the bow and stern which will need to be vented.

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The deck in the forward cockpit area is stitched together from five panels. Using several panels instead of a single panel bent ("tortured") over frames (the method Chesapeake Light Craft uses) keeps the deck from being under constant tension. It also simplifies sealing the underside of the deck, since the underside of the deck can be fiberglassed prior to installation.  In CLC kayaks, the underside of the deck is coated with epoxy only (no fiberglass) and installed while the epoxy is still wet.  

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Warren installed a "sheer clamp" around the inside of the sheer.  It looks like it's about a half-inch by half-inch length of cedar, tapered towards the ends. A rolling bevel along the top surface of the sheer clamp facilitates joining the hull and the deck. The sheer clamp helps keeps the hull fair, since the plywood is very flexible without any support.  In CLC kayaks, the deck is nailed to the sheer clamp. Nails are necessary because the deck is bent around a form and under tension. Since his deck isn't under tension, Warren says he can simply join the deck with a bead of thickened epoxy and avoid the appearance of ugly exposed nail heads. 

By the way, Warren is building this kayak in what is basically a large tent that he built in his backyard. If you talk to enough boat builders you can't help but be impressed with what people will go through to acquire workspace to build their boats. For instance, another friend of mine built his Pygmy Arctic Tern over a winter in a rented 10 x 20 ft unheated mini-storage unit, equipped with a single exposed lightbulb and one electrical outlet. 

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