catenary cuts?

[JustAnotherDude]

Searching the threads I haven't been able to find answers to some questions I have so I asked it in a thread by Klitsapcowboy on one of his tarps. I got a couple responses that make sense and a suggestion to open a new thread so, that's what I'm doing here.

The questions have to do with the title, catenary cuts, and his post indicated cuts had some impact on stretch and that material bias impacted it.

So:

1. What are catenary cuts for?
2. How do they work?
3. How does material bias impact them?
4. How do I read material bias?

Thanks

[kershaw]

What are catenary cuts for?
Weight loss; cat cuts remove fabric.
Bulk loss; same reason.
Most important reason is that cat cuts keep the fabric taut even when wet. This is not a problem with materials that don't soak up water like silpoly or mountain silnylon. Standard silnylon does soak up water and tends to sag without cat cuts. Cat cuts solve the problem of needing to re-tighten the tarp.

Best reason for cat cuts? They look amazingly cool!

How do they work?
Cat cuts remove the material that could flap in the wind. The curves keep a constant tension on the fabric resulting in an always taut pitched tarp.

How does material bias impact them?
In a tent with exact angles bias stretch will impact the shape of the project. I've made a couple of tarps in silpoly, silnylon and mountain sil from ripstopbytheroll and extremtextil. I've not found any noticable problems caused by bias stretch when using my tarps.

How do I read material bias?
The manufacturer of seller will give information about bias stretch; depending on the project you're making you'll need to choose the right fabric. A little stretch in high stress places will need the right fabric/ weave orientation. Sometimes a little stretch (silnylon) is preffered over rigid fabrics (silpoly) to give under stress caused by wind, snow, etc.

This is what I picked up so far. Hope this helps.

[Outdoorsman]

I have never heard of “Mountain silnylon”, I need to research that. Is it heavy? Expensive? Who makes tarps out of it?

[JustAnotherDude]

I have never heard of “Mountain silnylon”, I need to research that. Is it heavy? Expensive? Who makes tarps out of it?

I believe this is what kershaw is referring to:

https://ripstopbytheroll.com/collect...ountain-series

[P-Dub]

"Bias" in fabric refers to the stretch that occurs on the diagonal to the direction the threads run.

To demonstrate, take a bandana and pull two adjacent corners along one edge. Then hold two opposite corners (diagonally) and pull -- you'll notice that the cloth will feel stretchy. That is demonstrating the bias of the fabric.

When a tarp is staked out, a number of stresses pull across the bias, resulting in the potential for wrinkles due to the uneven tension. Cat cuts help decrease the possibilities for wrinkles.

[kershaw]

I believe this is what kershaw is referring to:

https://ripstopbytheroll.com/collect...ountain-series

Yes it is :-) It's nice stuff.

Forgot to mention silpoly doesn't stretch much so when wet; many make tarps without cat cuts and have taut pitched tarps during the night.

Silnylon does stretch; cat cuts are funcional.

Mountain sil has an in between stretch; doesn't stretch as much as silnylon but isn't 'rigid' as silpoly.