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  1. #1
    m00ch's Avatar
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    How do you fabricate a catenary cut ridge line in a DCF tarp?

    I am stumped on the procedures to fabricate a DCF tarp with a cat-cut ridgeline. Several companies offer it so obviously itís able to be done but I am just not wrapping my head around how the panels would be cut and bonded together.

    Does anyone have insight on this?


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  2. #2
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    this might help. https://backpackinglight.com/myog_te...tenary_curves/
    I have been looking into cat cuts also. I know that you can figure them by hanging a string between two nails in a wall, and drawing the line of the string. Taping paper to the wall before you start is recommended. It keeps your lady happier. (always important.) the cut at the ridge line is the same. My small 6x11 bends at the ridge but has no seam there. It could use some material removed on the outside edges, but it functions fine like it is. I don't think I'll change it.

  3. #3
    Senior Member ibgary's Avatar
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    Look up Dr. Hammock. I seem to remember a YouTube tutorial he put up on the subject. Maybe it was Professor Hammock, Shug probably knows.

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  4. #4
    m00ch's Avatar
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    Thanks for the responses but all that I can find is how to do a catenary curve using sewable and slightly stretchy fabrics and typically a flat-felled seam. I cannot understand how to translate this process to DCF where the ridgeline is one piece of DCF laid of the other with transfer tape and the material does not stretch.

  5. #5
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    Quote Originally Posted by m00ch View Post
    I am stumped on the procedures to fabricate a DCF tarp with a cat-cut ridgeline. Several companies offer it so obviously it’s able to be done but I am just not wrapping my head around how the panels would be cut and bonded together.

    Does anyone have insight on this?


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    You really do not need a cat cut on a DCF tarp. You need a cat cut on stretchy fabrics like silnylon. DCF has very low stretch and a cat cut does not provide enough benefit to make worth the extra effort. You'll probably be very happy with a straight ridge line and sides.

  6. #6
    m00ch's Avatar
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    WVwanderer - I have no doubt that you are correct about the performance of the DCF tarp without cat cuts on the ridgeline but since I have gone down this road, do you have any knowledge on how to do them?

    And why do so many manufacturers have a cat cut on their DCF tarp ridge lines if the benefit is so minimal?


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  7. #7
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    Quote Originally Posted by m00ch View Post
    I have no doubt that you are correct about the performance of the DCF tarp without cat cuts on the ridgeline but since I have gone down this road, do you have any knowledge on how to do them?

    And why do so many manufacturers have a cat cut on their DCF tarp ridge lines if the benefit is so minimal?
    Why? well, it may just be that it provides their sales people with a pitch point. More BS to make you think you "need" their product because it's better. Then everyone joins in because everyone wants their tarp to be the best.

    how would I do one? well calculating how much curve you would want comes first. I think I would start by cutting the pieces of the tarp oversize and stitching them together. (this is not the final seam. just 1 row, straight stitches as tight to the edge as possible. the purpose here is to hold the 2 peices together to get a measurement not to be a working seam. this will be referred to as the "temporary seam") Next, I would run a double ridge line. (2 side by side with equal tension) Mark the center of the temporary seam with a marker and place material over the ridge line. use temporary tie outs and stake out the tarp. Work the temporary seam between the 2 ridge lines and pull at the center mark until the the sheet of the tarp becomes taught. This will give you the distance of drop you will want in your curve. remove the fabric and pin (tape whatever) the straight temporary seam to a long wall with the fabric hanging down. run a piece of string with the correct drop and mark it lightly with a pencil. This is the wanted curve. Calculate how much material you need for a seam allowance and mark the curve again lightly a second time. this is where your seam will be. Lay the tarp sheet out flat with the 2 sides one on top of the other with your marks up and cut on the first mark removing all the temporary seam. sew you final seam.

  8. #8
    Senior Member WV's Avatar
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    Well, I agree with WVwanderer (though I wonder why he wandered [Hi, Ron!]). However, the technique I used for my "cuben fiber" tarps - that's what they were called then - with 3M adhesive transfer tape would work. It's an adhesive that works extremely well on polyester, sandwiched between two slick paper backing layers. There's no tape there, just the gummy adhesive and the paper backing. You remove the backing from one side and stick it to one edge of the tarp. Then you take the other half of the tarp and lay it on top of the transfer tape (with the paper backing still on). Use masking tape and weights at the ends of the seam to hold the two halves properly aligned. I suggest meditating for several hours or getting a good night's sleep before attempting this. Carefully pull a few inches of the paper backing off and bend it out from under the seam at a 45į angle. Then, working a few inches at a time, hold the top layer of the tarp down on the transfer tape as you pull the paper backing out from between the layers. The transfer instantly sticks. If you're using masking tape to hold the alignment, you'll need to remove it piece by piece as you go along before you pull the backing paper. This is not an easy task, but it's doable. The bad news is that this is how you do a straight seam. To bond a catenary curve is more difficult because the paper backing strips are stiff enough that they can't be bent into a curve to match the edge of the tarp material. Do it in 8" increments (starting with step 1). I used 1/2" wide adhesive transfer tape for cat cut edge seams on my cf tarps and 1" wide seams for the straight ridge lines. Experience with complicated cf insulated hammocks with curved baffles suggests that 1/2" wide seams would be strong enough for a ridge line. The seams with adhesive transfer tape are much stronger than the main tarp surface and very much stronger than any sewn seam. Anyway, that's how it could be done. By now the warning, "Don't try this at home!" should be ringing in your ears. Good luck.

  9. #9
    Senior Member WV's Avatar
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    By the way, Double E's method of measuring the desired depth of the cat cut is both logical and obsessive. It sounds like something I would do. If you use it, let us know what you come up with. An alternative SWAG is 7". The bonding method I described replaces "sew your final seam."

  10. #10
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    I don't know how HG does their catenary-cut ridgeline, but I can tell you my first DCF tarp was an HG standard with straight-cut ridgeline and it sucked big time. I couldn't get that tarp taut for love nor money. After about six months I dumped the straight-cut ridgeline and went with a Winter Palace cat-cut ridgeline. What a difference it made!
    "A foolish consistency is the hobgoblin of little minds." Ralph Waldo Emerson

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