Catenary Help

I've never done it, but I think I read that you can hang the material on the wall, then hang a rope with some slack in it along the ridgeline, and trace the rope. Like here – http://www.backpacking.net/makegear/cat-tarp/index.html

In the 5yds to SUL article Jay suggests copying the curve from another tarp. It should come out ok even though the length isn't the same.

-Tim

Hi Jamie

If you send me your email address I will send you a spreadsheet which allows you to calculate this for whatever dimensions you want.

Cheers
Roger@backpackinglight.com

Yes you can copy your Grace tarp. Start in the middle and work outward ignoring the extra length on each end.

The spreadsheet I posted in 2006 is still available.
2006 Spreadsheet

-Lance

Roger, is your chart a list of calculations, with a length variable, of points on a hyperbolic cosine curve?
By the way, I am not much of a regular poster but an avid reader here. I appreciate all your insightful articles and comments. Thanks.

It's a spreadsheet with a graph for pretties.
You can plug your figures into it – length of span and amount of sag. You get XY points along the line. Email with your address if you wish.

Cheers
roger@backpackinglight.com

So the part that gets me about MYOG cat-cut tarps is how do you sew the ridgeline? I have an Oware cat tarp, and the ridgeline appears to me a French seam (maybe flatfelled?), but with the curve, how does that work?

Pictures of the process, anyone?

Use a flat felled seam. The plans I work from have a 1" seam/hem allowance all around so I offset the two halves 2/3". One side gets 2/3" allowance, the other side gets 1-1/3" allowance. When the seam is finished, a total of 2" is used and the seam is perfectly centered.

Two halves 'right side' to 'right side' and offset 2/3" :

Sewing first seamline:

First seamline finished:

Sewing second line after opening up the two halves and rolling/folding the seam allowance (looking at the 'wrong' side):

OK, that's what I thought was done. I was worried about the tarp ridgeline buckling because of the slope of the curve. I guess it is not as severe as I thought.

Also: bookmarked page – all MYOG folks with an interest in cat tarps should, too.

There's been a lot of interest in my spreadsheet, so we will try to figure out how to make it publicaly available from BPL. Stay tuned.

I tried Google Docs, but they can't handle the embedded graph. Feeble.

Cheers

I'm sure many people would appreciate the spread sheet Roger. Thank you.

Lance, are the white lines you have on the tarp the markings for usable sleeping space? What pattern are you using, if you don't mind me asking?

The material in the above pictures is actually the fly portion of a tent I designed and made for myself. The white lines mark where the mesh walls attach to the fly.

More information and pictures in my 2007 Post

Hi Roger,
Just a bump to see if you've managed to figure out how to get the spreadsheet to work? No pressure, just being nosey.
Matt

I’ve put my 2006 catenary curve spreadsheet on-line. The spreadsheet was created using Microsoft XL 2002. The spreadsheet is at the bottom of the page and is 23kb. The web page works with Explorer v7. It should also work with other versions and other browsers, but I haven’t tested it.

Be patient, it’s slow.

Web page for Catenary Curve Spreadsheet

Let me know if it doesn’t work for you.

Lance,
I Just saw the photo of your tent, and have to say it looks like a piece of art. I wish I had the patience to something that clean. Very nice job.

Lance – this may be a dumb question, but looking at the spreadsheet curve, it starts and ends at 0. But looking at your tent, you obviously have a high and low side. So did you just use half the curve on the spreadsheet?

Oh and BTW – your spreadsheet hosting worked.

Kier:
The tent ridgeline uses the complete curve layout from zero to max back to zero. Here's a rough drawing of how the curve was layed over a straight ridge line. I overlayed it to intersect the straight ridgeline where the walls intersect. That way I didn't have to make adjustments to the wall pattern.

-Lance

OK now I think I got it. It doesn't matter what the height of each end of the tarp is, just the deflection from the original ridgeline? So first I decide the angle I want the ridgeline, then I plot the points from the graph, then I cut? So it doesn't matter even if I want something ridiculous like the tarp opening to be 6' high on one end and 1' high on the other? Thanks! so much easier

Or string a rope/cord/chain up.