5.5oz Cuben tarp with carbon tieouts

[Steve B]

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

[Harald Hope]

Very impressive, both in outcome and in your design/planning/testing process.

[Jeremy Platt]

Wow, very impressive!

[Jared Baker]

Love the detailed write up. Makes me want to do more projects in Cuben.

Good bit of information on the type of tape and on how the seams were done.

Thanks for the contribution.

[Daryl and Daryl]

Stephen,

Wonderful job! Your kite building experience shows. I'm impressed with the way that you rethought every detail of this project.

[Colin Krusor]

I agree with the others. Very ingenious design and meticulous execution. The finished weight is impressive, and it's unusual for a person making their first cuben tarp to try such a sophisticated and innovative approach to the problem of tie-outs.

[Jerry Adams]

Nice design, finished product, and write-up

Some day I may do a Cuben tarp and will refer to this

[spelt with a t]

That is gorgeous.

[David Cramton]

That's amazing work. Something to aspire to.

[brent driggers]

Wow. nice work! I have the materials and everything I need to do a very similar project but just cant pull the trigger to get started. Maybe now I will after seeing yours.
Thanks for posting

[Steve B]

Thanks for all the comments everyone! It took me quite a while to put it together, at one point I stopped working on it for a couple of months. An amazing feeling to spend so much time/thought and have it come together.

Got an idea for a serenity shelter like bivy that should weight 5.5oz also. 0.5oz cuben is lighter than Ultralight Insect Netting!

I'll edit the original post with the google sketch-up file later tonight (link? Attached? I'll figure it out…) Seam allowance of 1/2" will need to be added, as will the seam curves. Maybe someone with more sketch-up experience can turn the panels into something 3D :)

Steve

EDIT2: Dimension picture added to original post.

[Nick Gatel]

Very nice!

All the planning and preparation is why I don't try to make my own clothes, shelter, or pack.

[Evan Chartier]

This is so sweet! That is a fantastically tight pitch it seems. Awesome!

[Thomas Gauperaa]

When can I buy one? ;)

[Adam Kilpatrick]

Just found this thread Steve.

Your tarp is amazing! I expect that it will last….forever. Some fantastic ideas on tieout reinforcing, etc.

Do you think the pieces of carbon work well with a slightly bigger hole to accept a mini biner for easily removable guys?

Cheers!

[Steve B]

Thanks Adam! It will be at the Socal GGG coming up in April. I'm considering giving a small demo of how I did the ridge seams, and how I did the tie outs. Haven't talked to anyone about this, and I don't know if that is the venue to do such a thing. I'll ask around.

The size of the flat carbon for the tie-outs is a double edge sword. The bigger they are the more fabric they can pull, and a larger hole could be drilled (for biners like you suggested). The smaller they are the more the fabric can flex over them at the corners. I choose 1/2" wide somewhat arbitrarily. I had 1/2" wide 9460 tape, and it seemed right.

Hmmm, larger holes for small biners. I think that might be a stretch for the corners, but then those could be left on all the time. For the side tie-outs (where the fabric is flat with no bend) that might work out just fine. Slight weight penalty for larger carbon. I know the flat carbon does come in larger sizes. There might be a small durability issue with inserting a hard biner into the drilled hole repeatedly, but the hole could be coated with some sort of epoxy to protect the carbon fibers from abrasion.

For as how often I would need to tie-out the sides, I would just leave a small loop of cord and tie off to that as needed.

I'm thinking of setting it up at my normal height (main pole at 120cm), and sizing some bug netting to go from the side to the front. The bug netting would be attached with small pieces of low profile velcro. Similar to the classic look of a tarp-tent from Henry 12 years ago, but removable. I figure something to interfere with the skeeters is better than nothing. Gotta figure out what the weight would be.

Steve

Love this post and the look of the shelter Steve – great job!

[Adam Kilpatrick]

Thanks for the detailed response Steve.

Yeah, a small loop of spectra through the carbon hole would also work I guess. One thing I was wondering, is how do these types of tieouts go long term with rubbing from the cord? Does the cord start to abraid on the cuben? I guess that's easy noticed and fixed though, just tape or glue on another small layer or cuben over the top where it rubs.

I like the idea of velcro removable bug liner. I've been thinking of that kind of thing myself, but can't get my head around how to do it effectively, with minimal weight, and minimal fuss setting up in camp. Carefully lining up velcro every time would be a pain. Small glove hooks or similar onto tiny loops of cord could be much faster and more secure, but then would the gap between the tarp and the netting be larger? Or is it just better to permanently put netting edges on, and then build a bathtub floor to sit on top of them with just a few places where it hooks on? Or should I just build a really light bug bivy instead? Mosquitos that would work fine for me I know, but if I'm in Tassie in a leech infested area, it can be pretty nice to be able to sit up in shelter and not worry about the little guys crawling in. They could crawl in over the gap between velcro attached netting and tarp (they are good on the mesh, just can't get through it). I don't want to go with a full bug inner, as, gee, all those ounces… Hmm.

[Adam Kilpatrick]

I really like the strips of cuben tape radiating out from the tie outs. Looking at Steve Evan's tie out tests to failure, once there is a bit of reinforcement cuben near the tie out, after that its never the fabric that is reinforced or the tie out that actually fails, its the single layer main fabric just beyond that. Those radiating strips would help to spread that load much deeper into the body of the tarp, where it is wider, and thus able to absorb the strain more. Would be interesting to see Steve test this method on his rig for comparison.

[Steven Adeff]

ugh, I hate it when 3M's own spec sheets don't match measurements…

anyway, I've been looking to try different tapes, having used the 9485 I was looking at 9482 to go to a 2mil tape, but the 9460 looks very intriguing after your tests.

can I ask where you sourced your 9460 from? finding these in single roll purchases is quite difficult.

thanks!

[sam jepsen]

That is a truly impressive piece of work!

Is there an equation for determining the degree(?)/arch(?) of a catenary curve? Or do you just trim what would otherwise be a straight edge into what looks like a reasonable curve?

[Jerry Adams]

When I've free-handed curve it didn't come out right. There were wrinkles and such.

Both Roger and I have articles in make your own gear about tarps and catenary curves. I stole xls file from Roger. Make straight line. Mark every 2 inches. Measure distance from center for each point.

Or you can do this one time and make a pattern and then use it.

Or you can suspend a heavy line between two points and let it hang, and then trace this curve.

The exact curve isn't that important, but it has to be smooth or your tarp won't pitch tautly

[sam jepsen]

Thanks Jerry! I just looked up those posts.

[Nick Smolinske]

Stephen: In an astounding coincidence I was researching transfer tapes on Friday (for sealing Xpac seams) and found out that Amazon has 9460 rolls individually:

http://smile.amazon.com/gp/product/B004V40D5I/ref=s9_simh_gw_p328_d2_i5?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=0P3CDWDJWA03T459K3VD&pf_rd_t=101&pf_rd_p=1688200382&pf_rd_i=507846

That's the 0.5 inch, but they also have 1 inch.

[Steve B]

Sorry for the late reply, haven't checked this part of the forum in a while.

I got my 9460 from a local supplier, RS Hughes, her in Socal. They do mail order and the tape is expensive (relatively). The 1/4" 9460 I have I got from a kite supply store called Hang-em High Fabrics, since closed.

If anyone wants the excel spreadsheet I used to make the cant curve, just pm me with your email address and I'll attach it.

Steve

[Author]

Posts