5.5oz Cuben tarp with carbon tieouts
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I finished my first tarp. I made it from 0.5oz and 1.43oz cuben from zpacks, 3M 9460 double sided “tape”, 11mm x 1.75mm flat carbon (http://www.kitebuilder.com/catalog/product_info.php/cPath/239_236_62/products_id/1237 ), and a small piece of nylon.
There is not a single stich or any hydrosol glue. Bonded entirely out of tape.
Being my first tarp, and a cuben one at that, I did a bit of planning. I made a model around my MLD serenity shelter out of string, got the measurements as best I could (including angles), and built my panels in Google Sketchup. This allowed me to plan my fabric (which way the bias would go for the amount of fabric I would need). I then got some tyvek on ebay and built a model of the tarp. It was just as I wanted (at the time). Using the floor space at my work (cleaned well beforehand so the cuben didn’t get abraded), I marked and cut out the panels on the cuben.
I decided to use 3M 9460 over what Joe sells at zpacks after doing some testing. (I believe Joe sells 3M 9485). I set up a test of the two tapes; 1” wide with 35lbs hanging off it. The zpacks tape showed some creep, while the 9460 tape did not. I have never heard of anyone using a particular type of tape for energy absorption (and I doubt the tape can respond that fast anyway), so I felt that the less creep the better. I also have three different widths of the 9460 on hand from building kites, and I foresaw using all three (and I did).
For reinforcement at the poles and the tieouts, I used 1.43oz cuben. I applied multiple strips of 9460 tape to the heavy cuben, and then cut out my reinforcement pieces. No regrets on the size or weight of the reinforcements.
I used one inch of overlap along all seams, of which there were 4; two to join the end triangle, one along the main ridge, and one for the front beak. All of these are catenary curves; the end triangle and front beak seams are a 400 factor, and the main ridge is 700 factor (which gives a max deflection of 5cm). I don’t have a source for the excel program I found that gave me the measurements, but it is not Roger Caffin’s.
To get a one inch overlap between all the seams, I applied the half inch tape to either piece, exactly on the edge. One piece of tape goes on the right side of the fabric, one piece on the wrong side of the fabric. Overlap the two pieces; the tape backing goes edge to edge, like interlocking your two hands with the fingers cupped. I then taped, using household scotch tape, the edge of one of two panels to the other panel. Then I turned the whole thing over and scotch taped the other edge of the panel to the other panel. The scotch tape was temporary, as I did this on both sides thinking that I wanted to center the curved seam nearest where the edges of the tape backing were touching, to minimize any wrinkles (it is very hard to explain why I did this…)
I then turned the whole thing over again, pulled off the first scotch tape, and then pulled off the backing to the 9460 and taped it down. To the other side; pull off the other scotch tape and pull off the backing to the 9460 and taped it down. Result: not a single wrinkle along the entire catenary curve, no gap between the two half inch wide tapes, and the process was very easy! No weights, clamps, or waiting for things to dry.
I had tested using small pieces of flat nylon for tiouts, but found that the hole can elongate or rip through under a strong shock load. I had purchased some flat carbon for another project that didn’t happen, and it turned out to be close to perfect. The edges of the carbon were very well rounded with sandpaper to prevent cutting through the cuben.
For edge treatment, I ended up with quarter inch double roll over the small flat carbon pieces. The heavy reinforcement wraps around the outside edge of the carbon, and the carbon is pressing on the inside of the rolled hem.
Each carbon piece had the flat edge oriented perpendicular to the expected direction of pull, so that strips of half inch wide cuben tape could be applied to distribute the pull. Pictures show more than I can write… Holes were drilled to accept the guy lines after the edges were done.
The front pole support guy line is attached with heavy cuben tape, extending back along the topside of the main ridge for about six inches. A one inch wide piece of flat carbon is sandwiched in the heavy cuben, and a hole is drilled for the guy line. All edges are taped up to prevent separation due to the top of the pole being a curved surface that the tape sits on.
The foot end support is special; this part of the tarp doesn’t naturally form an underside pocket (like the front pole support), so the pole needs to be fixed in place. I taped on the underside a small, rounded piece of nylon, applied cuben tape over it, and then drilled a hole to accept my foot pole (could be drilled bigger to accept a hiking pole)(I use a foot pole to free up my hiking pole for camera duty). A hole is drilled to attach the rear guy line to. I used nylon for this because 1)I didn’t have any carbon this big and 2)I wanted this flat nylon to be easy on the cuben by flexing.
The micro line-locs for the guy lines are great; no need for strips of cuben that can peel apart when used with Lineloc 3 Line adjusters. If the line is too long, then I just choke up on the line by tying a removable knot in the end line. Only downside is that I can’t adjust things from inside the tarp.
Total weight is 5.5oz with guy lines, 12 edge tieouts, and 2 pole tieouts. Ridgeline, from pole to pole is 8.76 feet (2.67m). Shown picture is using my hiking pole set at 100cm.
EDIT: Here are the dimensions. Numbers without units are angles.
Steve
@rememberthelorax
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