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Old 08-02-2008   #21
Chip's Avatar
SE, Wyoming
Paddling Since: 1986
Join Date: Apr 2007
Posts: 1,098
Centerboards & Bamboo

Pretty odd thread, but it zig-zags in an interesting way.

About bamboo, I've seen photos of it used for crossmembers on amas (outrigger hulls) and for masts and spars. Also for scaffolding on construction projects, house framing, et many ceteras. Neat stuff, about which I know very little. But the arrangement of longitudinal fibers in a woody matrix is similar to carbon fiber layups. Seems like a lot of products made of laminated bamboo are coming on the market.

On the sailing rig, my first setup was a pivoting centerboard with a loop of shockcord up top so if I hit a rock it'd spring up. Worked so-so. Then I built two pivoting leeboards (also paddle blades). That seemed a bit better, perhaps because when the thing was heeled there was more blade in the water. (Naturally, I'd raise the foils to go downwind.) Still, it didn't maintain hull speed well enough to tack— I could get over maybe two times in ten.

Paddle blades aren't the right shape for underwater foils, of course, but the idea was to figure out a sailing rig that used paddle shafts for a mast and spars, and blades for a rudder and foils, so I wouldn't have to carry a lot of extra stuff. It did go upwind although you couldn't sail close hauled— it took constant trimming up and pinching and bearing off. Plus laying across a pair of cat tubes is uncomfortable as hell.

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Here's a photo of it with a gaff rig and the pivoting leeboards. Not much sail area. I also made a wee jib for it— sort of a handful to manage two sails plus the leeboards and rudder.


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Old 08-02-2008   #22
Chip's Avatar
SE, Wyoming
Paddling Since: 1986
Join Date: Apr 2007
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Curiouser and curiouser. . .

A few more riffs, before sleep.

a) Really efficient inflatable hulls, for instance:

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This is the bow of a Happy Cat Light made by Grabner. The open-ended baffles shape the hull so that it steps up with increasing speed. The practical effect for a whitewater boat would be to lift the tube when you row against the current (thus increasing the velocity of the water along the tube). This would decrease the wetted area and make it easier to maneuver. For most rapids, the shaped bow would face upstream (or it could be a double-ender).

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b) Catapult (UK). Inflatable tubes for flotation, metal for stiffness and structure, and molded or laid-up stuff (?) for the cutting edge. These things are said to have touched 17 knots, which is bloody quick for a boat this small. Any reason a river cat couldn't be made like this? With the bows shaped of hard foam and skinned: replace as necessary.

c) A hardshell whitewater cat. Get a pair of roto-molded double kayaks. Mount 'em with a breakdown aluminum rowing frame. Put flotation in the ends and make bombproof hatch covers so you could stow cargo in the cockpit area (keeping the center of gravity low). You could also rig gear on the frame in the usual way. They'd be a lot more hydrodynamic than the standard cat tube. You could trailer it, or break it down to haul the 'yaks on a roof rack with the frame inside the vehicle. I think it'd have a cargo capacity equal to a standard cat, and row like a dream.

So many ideas— and life's too short.


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Old 08-03-2008   #23
no tengo
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Baytopia, Colorado
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I am still trying to build a cat frame that will fit in a checked airline bag. It must be less than 60 linear inches (W+L+H) and weigh less than 50 lbs. Darn near impossible on a 14' cat. My best bet so far is using NRS and having the pieces break down but then the break down couplings (aluminum rod) add to the overall weight and their oar towers weigh a ton. Would certainly have to skip the seat and use a piece of plastic or something. I wanted to try to get the cross tubes that hold the seat to fit inside the end tubes to save on space - but then you need a T pipe fitting that has two different sizes. Fittings overall weigh a lot - so bending is better where possible but adds to the space taken up by the frame.

some day we shall figure it out.
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Old 08-03-2008   #24
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SE, Wyoming
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Semi-Impossible Dream

The checked baggage spec is pretty severe. I can't see any way to do it with NRS tubing (1-5/8" OD). Plus the LowePro joints and oar towers are pretty heavy.

Since the larger size chain-link toprail tubing is also 1-5/8, you could fly with a bag of SpeedRail fittings and a tubing cutter, buy tubing and dowel on the spot, and build it at the put-in.

For SpeedRail fittings, look at <>. $100 minimum order. Their nominal pipe sizes can be confusing: the 1-1/4" fittings match NRS 1-5/8" OD tube. You can download a catalog and a pricelist.

I just got the SpeedRail fittings for a cat frame of 1" OD tube. Next I have to buy the tubing. <> looks like a good source. The oar towers might take a while to figure out.


Good luck with your project.
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Old 08-03-2008   #25
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SE, Wyoming
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Quote: "Would certainly have to skip the seat and use a piece of plastic or something. I wanted to try to get the cross tubes that hold the seat to fit inside the end tubes to save on space - but then you need a T pipe fitting that has two different sizes."

A couple more thoughts: the lightest really comfortable seat is the trampoline type with an inflatable back cushion— check the Jack's Plastic Welding website <> and look at the Cutthroat. I just made one for a Shredder frame I built, and ordered the pillow from Jack's. Probably simplest to get the seat made by Jack's to order. It packs really small.

To reduce tubing size, you can cut short sections (2") of the larger size tubing and slip them over the smaller, then braise, MIG weld, epoxy, or pop-rivet one end in place. The other end sleeve could be fixed with a machine screw & acorn nut, etc. so you could remove it. That'd let you slip the smaller tube inside the larger piece. I've done this sort of thing to fit 1" EMT conduit to 1.315" SpeedRail joints.

One thing that confused me was that some commercial suppliers use nominal or IPS (Iron Pipe Size) measures that differ from actual dimensions. For instance a SpeedRail 3/4" IPS fitting actually goes with tubing that's 1.05" OD, while the 1" IPS fits tubing that's 1.315" OD, and 1-1/4" IPS fits 1.66" tube— the same size as NRS uses in their frames.

Maybe you already know all that. I learned about it by ordering the wrong stuff.

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Old 08-11-2008   #26
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SE, Wyoming
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Tube size (no— not that one!)

Wee update on the ultra-light frame crusade.

Ordered a couple feet of the 1" OD, 0.125" wall alu tube from <>. Good thing I got a sample before ordering a bundle: it doesn't fit the SpeedRail joints (3/4" IPS which is bloodywell 1.0625" ID in the real world). Why can't they list stuff by the actual dimensions?

Another discovery— for bits & pieces of aluminum, hit the local salvage yard and ask permission to check out their bin(s) of 6061 alloy. I scored scrap t-rail, flats and square rod that'd cost about $50 new for $7.50. I'm laying out some light but very strong oar towers (for the frame that I'm still trying to locate tubing for).

Good luck with your own mad obsession.

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Old 08-11-2008   #27
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Lakewood, Colorado
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Alreco is the place to go in Denver. I would take your fittings and such over there and try out the fit before hand. Plus, they have all kinds of stuff there and I'm sure they would let you poke through the remnants pile.


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