Cat Curve on a Pyramid

[Chris M]

With my job this summer, I have a lot more time to make gear than I do to actually use it. One thing I have been looking at making is something similar to the MLD Duomid. Really just a good two person shelter to help me get my cheap friends out hiking with me or give my dog some space under a tarp.

My thought with the mid is to set it up using a inverted V pole set up by using extenders on my trekking poles, which are fixed length. The extenders I could then use in my pack as a frame. I think they need to be about 18" to get a good height and width using my 120cm trekking poles, which I think could work well in my homemade G4.

The one thing I'm not sure on is putting a cat curve. I've made one tarp in the past, but I didn't put a cat curve in it. Two questions about this. First, it seems to me that a cat curve is going to really make the mid a much better shelter. Will it really make that much of a difference, or is this something I could just skip. The tricky question is what is the best way to go about planning out the cat curves along these pieces? I have read the article on making a cat curve, but it was made for two ends that would be at relatively the same height. The mid doesn't seem to match that case, but would the chart in the article still work? Thanks for any help. I'm really excited about this shelter and appreciate any help that I can get here.

[Jerry Adams]

I think the Cat curve makes the tent more taut – flaps around less in the wind

Otherwise there will be a loose flap of fabric at the ridge

I don't think it makes any difference whether the two ends are at the same height or a different height. I used Roger's spreadsheet on the 4 ridges of a pyramid and it worked great. Just measure and cut meticulously.

I've tried suspending a string next to a pattern board and tracing it but the result wasn't as good.

I've tried making the tent with a straight ridge, setting it up, pulling on the fabric along the ridgeline and putting in hand stitches, then going back and finishing the seam, but it didn't end up as smooth.

Maybe you should just make a simple pyramid, like in the article in MYOG. Easier to make. Big enough that there's plenty of headroom.

[Eddie Rivera]

> The tricky question is what is the best way to go about planning out the cat curves along these pieces? I have read the article on making a cat curve, but it was made for two ends that would be at relatively the same height.

The hammock forums actually have a number of discussions on cat curves for various tarps. I recently made a hex tarp with cat curves along each edge.

There is an spreadsheet that may help, but it initially assumes that both ends are at the same height. I have a hard time picturing what that type of cat curve looks like… wouldn't that mean it's not symmetric, and thus defeat the purpose? Regardless of the start and ending points, I would think the cat curve is symmetric along that line.

In this tutorial for the tarp, there are links about halfway down that include links to the xls, if you're interested.

http://www.hammockforums.net/index.php?page=blackcat

[Chris M]

Jerry, it seems that the 2 person silnylon pyramid article used Roger's spreadsheet to make the cat curve as well. If I remember the article written with that spreadsheet correctly, one of the two values you manipulate on the sheet are the half length of the curve as well as the depth of the curve. What depth did you find to work well for your pyramid? My initial thought was to try a shallow depth, pin it together and see how it pitched somehow. And then slowly work to a greater depth if it didn't work. Is this the best way to go about it?

The mid in the article is a good design, but it is just more shelter than I really need. I just planned to go about making something a bit smaller. Thanks for all the information. Anymore thoughts, recommendations or techniques for doing this would be much appreciated.

[Logan K]

I've made a few shelters over the last couple of years and used cat curves of different depths on each. The cat curve helps to shed wind by moving the wind load to the tie outs from the panel. Tarps with cat curves are quieter than those without, for example.

I tried to "science" my way through the process, and ultimately decided to just wing it and see what worked. My first tarp (11 X 11 Hammock tarp) has big curves (4 inch depth) where as my solo shelter (think MLD Grace) has pretty shallow at 2 inches. The bigger the panel size, the deeper the curve needed I think – but I don't se much reason to exceed 5 inches or so even on a huge panel.

My "cat curve generator" is a strip of 90 degree angled vinyl corner moulding from Lowe's. It has an even flex along the entire length and can be pinned with thumbtacks to hold any curve I can ever thing of using – all for about $3 including thumb tacks! Trace curve line with sharpie and viola!

Hope this helps,

Logan

[Jerry Adams]

I used 2.5 inches deflection on a length of 95 inches

Since then I've looked at it and thought another inch would be good

So, maybe 3.5 inches on 95 inches would be good

You could easily make it a different size including non-square base. I could verify your calculations.

You could also use a flexible board to make a curve. It wouldn't be a mathematical catenary curve, but I don't think it would matter.

[Greg Mihalik]

"You could also use a flexible board to make a curve. It wouldn't be a mathematical catenary curve, but I don't think it would matter."

Gravity, Science, Math….all over rated. Just do what looks good.

[Jerry Adams]

I've tried suspending a string and then marking along it's length to make a curve, and I tried Roger's spreadsheet.

Using the spreadsheet resulted in a smoother curve. In the finished tent the fabric was more evenly taut with no wrinkles or anything.

But, maybe it was just that my sewing consistency improved.

[Author]

Posts