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Discussion Starter #1
Hello all,

I have been working on a new design for a cat frame. However, I have been too swamped with my day job to work as much on it as I would like. So, I figured I would throw it up here and see what people think.

I am working on this design so that I can have a full size cat that I can hike into remote rivers. Plus, I want a craft that can run difficult whitewater that is outside what a packraft can do. In the end, the goal is to have a boat that split between two people is 20lb a person. Based on modeling this frame in solid works and using single chamber tubes I think this is possible.

The basic idea is to use the rigidity of the tubes to replace the frame members in a conventional cat that run the length of the long axis of the tubes. In order to do this, the cross bars are fixed rigidly to the tubes so that they can also transfer moments to the tubes. Below is a render of the design that does not show the lace in system.


The next photo shows a proof of concept I have made.


When the cord is tighened down, I cannot move the cross member relative to the tube. Here is a close up.


I have not worked on the seating arrangement. I plan on having a setup like the Russian cat frames where the paddlers kneel on the tube.

The only reason I do not have a complete boat is that, I (with my lack of gluing experience) have messed up gluing 4 grommet strips on in a row. When I try and lay them on the curved surface, I end up sticking the grommet strip to itself and ruining the strip. Also, I really want the grommet strips to be made by someone with a rf welder. I have tried for months to get a local shop to work with me, but seemingly no amount of money will get them to work on a halfday job.

Thus, if anyone in Eugene has any leads on a shop that can do rf welding around Eugene/Springfield that would be awesome. Also, if anyone wants to help me work on this project, I have all the materials for finishing the full prototype and I own a 3000sqft techshop style co-working space in Eugene that we could use to work on it.

Best,
Eric Harvey
 

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Looks cool. If you're going for a R2 craft why not use inflatable cross tubes like a Hyside Paddle Cat or an Airtight Inflatables Shredder? Both are about 45 lbs and capable of running class V with good paddlers. Do you want to be able to row it? I have looked at the Row Saddle from Soar (about 2/3rds down the page) for a lightweight way to mount oars to a frameless cataraft. I like your lace in design - I haven't seen anything like that on a raft before.
 

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What prevents twisting of the entire cat?....one side advancing when the other center punches a rock? How are those forces accounted for?

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I like the idea, but I think osseous has a point with the twisting issue.

Im in denver and I dont have an RF welder but could glue you up some grommet strips if you'd like. Give me a buzz if you wanna chat about it.


Have a look at the Jacks Plastic Culebra or culebra grande if you want a bigger boat. It is a paddle cat design but comes apart into pieces.
 

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Discussion Starter #5
Worries about twisting have come up when I have talked with others about this.

Just for ease of discussion, I am going to call the long axis of the tubes the x axis, the axis across the tubes the y axis, and elevation z.

If you try and move the cross bar in the x-y axis, it is restrained by two things. First, because the curve matches the tube, the tube itself resists any movement in the x-y plane. This is because as you try and rotate the cross bar, the effective cross section of the tube gets bigger. Second, the grommet strips are fairly rigid in maintaining a 90 degree orientation of the cross bar to the tube.

Now, for twisting in the y-z plane, the grommet strip psychically restricts the cross bar from rotating toward the outside of the boat. As for the cross bar rotating toward the inside of the tube, friction from the grommet strip and the force acting on the far tube prevent this.

Twisting in the x-z plane resisted solely by the the grommet strip physically restraining the cross bar.

Here is a look at the grommet strip:



The lacing on the cross bar holds the cross bar totally rigid (for an inflatable) basically because it is really tight. It is easy to do this by deflating the tube lacing in the bar and then reflating the tube. When the tube is tight, I could not get the bar to move relative to the cat tube. This is with a buddy holding the tube and me using the cross bar as a 4 foot lever arm. With 3 cross bars spanning the tubes, I think the boat would be pretty stiff. With currently frame designs, the rigidity of tube is simply not used because the cam straps cannot transfer a moment. With this design, the tube because a structural piece of the frame. For an example of the stiffness of inflated tubes, think of the overhead piece on a creature craft.

As for why not using inflatable tubes? I guess that works, but the boats I have seen out there that are out there that are inflatable are heavy and small. My goal is a 12' cat that comes in at 40lb total. Also, it has to split into 2 packages. Plus, I think this design would have the flexibility to be rowed, or paddled without purchasing a separate frame.

Plus, its just fun to build stuff. :D
 

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Interesting- good luck with it. Hope you keep us posted on your results.

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I think if you start on small water and work your way up learning its limits as you go its a great idea, and it is fun to build stuff.

If you cant find anyone local to weld you up some grommet strips and you want me to build you some I could have them done and shipped up to you in a couple weeks. Send me a drawing with dimensions, grommet size, etc. I'll make one and send it to you. You can see what you think. Using stabond on PVC always delams the material before it fails if its set right, so the glue is the last think i'd be worried about.

FWIW.The jacks plastic culebra is almost 12' and it weighs 50 lbs. It does come apart to split into two packages. I'm not saying to just buy a culebra instead of making your rig, just saying you should have a look at it if you havent.
 
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