DIY Cat Cut Tarp - Ridgeline Question

**Lonely Raven** · 08-09-2010, 10:11

So I've had the material for a week now (heavy stuff unfortunately) and my thread arrived on Saturday. I have a big spool of ball-chain on the way to help me draw out the catenary curves...

But I have one question. Is a catenary cut necessary for the ridgeline? If it makes any difference, it's going to be a 12' long, heavy (3.0oz/yard), winter door style tarp.

Thoughts?

**PuckerFactor** · 08-09-2010, 23:50

If you're cat cutting the edges, I doubt you'll need to, but a relatively shallow (2"-3") cat cut ridgeline couldn't hurt.

Acer

WV · 08-10-2010, 07:23

If you have a seam at the ridgeline anyway, you might as well make it a cat cut.
The ball chain sounds like a good idea - pretty snazzy! I used a piece of rope and traced the curve on a sheet of masonite, then cut it out with an electric jig saw. I've used that pattern on quite a few cat cuts by now. It was well worth the materials and the effort. However, if you've got a place you could pin up your fabric and hang the chain next to it, you can tailor the catenary to the length of the fabric and depth of cut more easily. Post a photo of your setup if you can.

**Just Jeff** · 08-10-2010, 07:39

Tarps with cat cut ridgelines technically have an "optimal pitch angle" where the tarp performs best. How much impact that has on the tarp's performance when it's not at that optimal angle depends on how aggressive the cat cut is.

Warbonnet puts catenary ridgelines on his tarps.* OES does not use catenary ridgelines on the MacCats. Both are excellent tarps.

I think you'll be pleased either way, as long as you get a good seam.

*I haven't measured a Warbonnet ridgeline but it doesn't look like a true catenary, defined mathematically. But for hammock purposes, it doesn't really matter if it's mathematically catenary or not...it serves the same purpose. To me, his design looks like it takes up slack and tries to minimize a catenary's disadvantage of taking up headroom right over the hammock. But I don't own a Warbonnet tarp so that opinion is based on appearance.

**Lonely Raven** · 08-10-2010, 09:31

Originally Posted by Just Jeff

Tarps with cat cut ridgelines technically have an "optimal pitch angle" where the tarp performs best. How much impact that has on the tarp's performance when it's not at that optimal angle depends on how aggressive the cat cut is.

Warbonnet puts catenary ridgelines on his tarps.* OES does not use catenary ridgelines on the MacCats. Both are excellent tarps.

I think you'll be pleased either way, as long as you get a good seam.

*I haven't measured a Warbonnet ridgeline but it doesn't look like a true catenary, defined mathematically. But for hammock purposes, it doesn't really matter if it's mathematically catenary or not...it serves the same purpose. To me, his design looks like it takes up slack and tries to minimize a catenary's disadvantage of taking up headroom right over the hammock. But I don't own a Warbonnet tarp so that opinion is based on appearance.

That's some good point of view, thank you for that. I guess in the end, it's still just a tarp.

I just figure if I'm making it, I might as well make it the best that I can. That said, I PM'd sclittlefield with the question, and he got back to me after I had posted this thread, his response:

"If you're cat-cutting the outer edges, I would not recommend cat-cutting the ridgeline. It's an "either/or" not "both/and" kind of thing. "

I really like the looks of the BWDD gear, so I think I'll follow that advice and see how it works out. The material I'm using is a heavy 3.0oz waterproof camo print. So I have a feeling my tarp would be a special case regardless of which direction I went.

Originally Posted by WV

If you have a seam at the ridgeline anyway, you might as well make it a cat cut.
The ball chain sounds like a good idea - pretty snazzy! I used a piece of rope and traced the curve on a sheet of masonite, then cut it out with an electric jig saw. I've used that pattern on quite a few cat cuts by now. It was well worth the materials and the effort. However, if you've got a place you could pin up your fabric and hang the chain next to it, you can tailor the catenary to the length of the fabric and depth of cut more easily. Post a photo of your setup if you can.

I got the ball chain idea from reading up here. IMHO, I believe that having a proper chain vs just a rope makes a difference in how the curve is formed. sclittlefield did recommend I could use lamp cord, but I do believe the curve would be different.

Again, all that said, it's still just a tarp, not a space ship. So any curve is better than no curve. I'm just being this specific for the geek/learning factor.

One of my hobbies is photography, so I plan on taking photos of the process, and the final product. If I turn out to be good at this sewing tarps thing, I have a feeling I'm going to be making a few for my camping buddies and will have lots of chance for practice and photos.

WV · 08-10-2010, 09:58

Originally Posted by Lonely Raven

I got the ball chain idea from reading up here. IMHO, I believe that having a proper chain vs just a rope makes a difference in how the curve is formed. sclittlefield did recommend I could use lamp cord, but I do believe the curve would be different. I agree.

Again, all that said, it's still just a tarp, not a space ship. So any curve is better than no curve. I agree with that, too.

I'm just being this specific for the geek/learning factor. I'm familiar with that rationalization. If you're interested, we have a "Recovering Perfectionist" support group, with meetings 3 x a day, 5 days a week and a weekend hotline.

One of my hobbies is photography, so I plan on taking photos of the process, and the final product. If I turn out to be good at this sewing tarps thing, I have a feeling I'm going to be making a few for my camping buddies and will have lots of chance for practice and photos.

Looking forward to the pics. Beware, the more time you spend making gear, the less time you get to spend in the woods.

**sclittlefield** · 08-10-2010, 10:07

Originally Posted by Lonely Raven

That said, I PM'd sclittlefield with the question, and he got back to me after I had posted this thread, his response:

"If you're cat-cutting the outer edges, I would not recommend cat-cutting the ridgeline. It's an "either/or" not "both/and" kind of thing. "

I really like the looks of the BWDD gear, so I think I'll follow that advice and see how it works out. The material I'm using is a heavy 3.0oz waterproof camo print. So I have a feeling my tarp would be a special case regardless of which direction I went.

I got the ball chain idea from reading up here. IMHO, I believe that having a proper chain vs just a rope makes a difference in how the curve is formed. sclittlefield did recommend I could use lamp cord, but I do believe the curve would be different.

It'll be a bit heavier, but should perform just fine. At that weight fabric, I would definitely recommend adding side panel pulls. You may not always use them, but you'll be glad they're there when you need them.

If I said "lamp cord", sorry. I meant "light cord". It was late. By the time you account for minor tracing and cutting errors and hemming, anything you use that has good drape for the curve will end up being about the same anyway.

Looking forward to finish pics.

**Lonely Raven** · 08-10-2010, 10:13

Originally Posted by WV

Looking forward to the pics. Beware, the more time you spend making gear, the less time you get to spend in the woods.

Unfortunately I'm already quite aware of this. Between working on the house after am minor electrical fire, two new puppies, a busy work schedule, and too many hobbies (and no money to do them)...the closest to the woods I've been getting is the deck on my back yard. I has *two* trees on either side so I can pretend I'm in the woods.

It doesn't help that Illinois charges $15-$25 *per person*(!) for campgrounds.

Originally Posted by WV

"Recovering Perfectionist" support group, with meetings 3 x a day, 5 days a week and a weekend hotline.

But only (promptly) between the hours of 8am-9am, 1pm-2pm, 4pm-5pm, and the hotline charges *Exactly* .31415926535 a minute.

**Lonely Raven** · 08-10-2010, 10:16

Originally Posted by sclittlefield

It'll be a bit heavier, but should perform just fine. At that weight fabric, I would definitely recommend adding side panel pulls. You may not always use them, but you'll be glad they're there when you need them.

Already part of the plan. It's going to be a BIG tarp. I managed to track down some 3m reflective bungee for the side pull tie outs so I don't closeline myself in the dark.

Thank you again for your guidance!