November 20, 2015 8:16 PM MST - Subscription purchasing, account maintenance, forum profile maintenance, new account registration, and forum posting have been disabled
as we prepare our databases for the final migration to our new server next week. Stay tuned here for more details.
Subscribe Contribute Advertise Facebook Twitter Instagram Forums Newsletter
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.


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:

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


Keith Selbo
(herman666) - F - M

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.