Forum Index » Make Your Own Gear » Types of Catenary Cuts??


Display Avatars Sort By:
Tom Clark
(TomClark) - MLife

Locale: East Coast
Types of Catenary Cuts?? on 09/02/2010 19:44:42 MDT Print View

Are there different types of catenary cut ridgelines? I realize they follow a hyperbolic cosine function, but how is the "a" parameter chosen for tarps & tents? Is there only one type for all manufacturers?

Thanks in advance for educating me.

Tom

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
catenaries on 09/02/2010 23:20:41 MDT Print View

They are all the same curve. We have an article on it in fact:
http://www.backpackinglight.com/cgi-bin/backpackinglight/myog_tech_note_catenary_curves.html

How do you choose 'a'?
:-)
Whatever seems like a fair thing to you!

Cheers

Keith Selbo
(herman666) - F

Locale: Northern Virginia
six o' one, half dozen o' tother on 09/04/2010 19:29:35 MDT Print View

I downloaded the spreadsheet from this site and computed some curves. I don't have the numbers anymore, but the difference between a centenary with a 6 in displacement over 8' and the arc of a circle was negligible. I think it was around 0.016. I just use a circular arc.

Paul McLaughlin
(paul) - MLife
Re: Types of Catenary Cuts?? on 09/07/2010 17:43:06 MDT Print View

Having sewed a number of tents using a simple arc of a circle in lieu of a geometrically correct catenary curve, I can attest that it works just fine. As another poster suggested, the arc will be very close to the theoretical curve when you are talking in terms of a few inches of deflection in a seam several feet long.
I've had pretty good luck using about 1/4" deviation from straight per foot of seam length - so if your seam is 8 feet long, each piece would have an arc such that the center of the arc would be 2" away from the straight line between the two ends of the line.