Cat cut- a quick alternative?

[Rat]

Wow, I just wasted 15 minutes trying to figure out the difference between a Catenary Curve and a Parabola! Can I have that 15 minutes back, please?

Hang a chain from two points to get a cat curve.
Do a lot of math, build a cone and do a lot of math or throw something and do a lot of math to get a Parabola!

My apologies to the engineers, I hate math.

[SmokeHouse]

Hogn8r,
This sounds like an excellent technique. I am continually impressed with the ingenuity of the members of this forum. One question, how do you know what the "deepest point of the cat cut" should be?

The tarp I made has an 11' Ridgeline, at center measure 4" down and lower Hogn8r chain to that. Thats the cat cut drop I use. Works great for me... But I used cardboard for a pattern.

[Rat]

The tarp I made has an 11' Ridgeline, at center measure 4" down and lower Hogn8r chain to that. Thats the cat cut drop I use. Works great for me... But I used cardboard for a pattern.

Interesting, I don't use a cat cut on my ridgeline seam.

[sclittlefield]

Hogn8r, One question, how do you know what the "deepest point of the cat cut" should be?

What Hogn8r said. 1" per foot works pretty well and is pretty much the standard on my tarps.

Having deeper cat cuts will give you a taughter (?) pitch.

Yup. And it's "taut". It's one of those words we use a lot here and is just way too easy to misspell. My first inclination is always to spell it taught as well.

Main Entry: taut
Pronunciation: ˈtȯt
Function: adjective
Etymology: Middle English tought, perhaps from tought, toughth fierce, tough, alteration of tough tough
Date: 14th century

1 a : having no give or slack : tightly drawn <a taut rope> b : high-strung, tense <taut nerves>
2 a : kept in proper order or condition <a taut ship> b (1) : not loose or flabby <taut muscles> (2) : marked by economy of structure and detail <a taut story>

The tarp I made has an 11' Ridgeline, at center measure 4" down and lower Hogn8r chain to that. Thats the cat cut drop I use. Works great for me... But I used cardboard for a pattern.

You should definitely check out the large tarp Smokehouse did with the 4" ridgeline cat-cut. It's fantastic and (thank you again Smokehouse) was the inspiration behind my "Winter Dream" tarp. If just doing the ridgeline is as easy for you as the edges, I don't see any reason not to simply replicate his tarp.

P.S. - Take a look at my website and tarp designs, if you like any of them I'm more than happy to help you out with some more specific details on building your own.

[TeeDee]

Before you go the trouble of measuring a "cat cut" (or something close enough ) and then the even more trouble of sewing it, take a look at Frawg's experiments. Could be that sewing a straight line could be "close enough" also.

[Frawg]

Just thinking out loud & seat of the pants here, but ...the parabola and the cat curve (cosh, a hyperbolic cosine) ought to be pretty close, given the shallowness of the curves we're making. If you do a power series expansion of the cosh function, there will be no odd-powered terms. The first order approximation just has a constant (ignorable, for our purposes) plus an x**2 term -- i.e., a parabola. Adding the second ( x**4 ) term of the series won't have much affect at all if the curve is shallow. If x is .1, for example, x**2 is .01 and x**4 is .0001. The pen you use to draw the curve will probably be fatter than the difference between the two.

[NickJ]

Throw into the mix that the fabric is not solid, and hence when the tarp is staked out the curve is unlikely to be true due to unequal forces being exerted on different guys, and one wonders whether it's worth the effort at all, apart from to draw a basic curve on a pattern and use that.

[Rosomaha]

I have one question.
I am planning to sew a tart with catenary depth near 10 inches. I want to make a triangle cutting with rolling and sewing of edjes, i suppose that on big tarp`s side triangle rolled-sewed cutenary would seems like curve.
Does my idea is clear? Sorry i dont know "tarp terminology". Thanks.

[TinaLouise]

you read the experiments on the forums and then pick a number, any number and try it out. I like about 6" but that's me.

Finally, someone else has said exactly what I ended up doing!!!

I read everything here, I checked out all the web-sites (and thank-you very much to the web sites that had pictures & drawings of the cat-cut tarps). Then I laid out the silnylon on the floor, my silnylon is dark purple so I couldn't draw on it, ended up using tailers chaulk to mark the cuts. Used a measuring tape to divide up the tarp edges evenly. Marked how deep I wanted to have the cat-cut go and then "eye-balled" the curve!!!! My tarp has a 11' ridgeline (11x10 tarp). Hung it up in the back yard yesterday for the first time. Worked great, I'm trying it out this weekend on a camping trip & it's supposed to rain so it should be a pretty good test.
Some other things I found out: tailers chaulk doesn't stay on the silnylon for long!! Don't walk on silnylon, I just about broke a leg!! Get some plastic clamps to hold the edges of the silnylon together.
TinaLouise

[vitamaltz]

I always use a tape measure to mark out the centerpoint and the depth of the cut, then bend the same tape measure in an arc to get the curve. A barbell in the middle holds the tape at the centerpoint, and a barbell at either end holds the tape there. I can trace along the tape. I'm like TL - any more effort than that would only give me a false sense of accuracy.