9′ x9′ tarp with 0.48oz Cuben

That sounds about ideal actually. You'd probably have to do some actual tests to figure out an optimum % though. If you have the time/money/energy you could buy one of those UV sun lamps and test various %s of coated Vectran. Leave them under the lamp for a a few days and visibly inspect (vectran I believe turns brown from gold with UV damage). Ultimately doing a stress test.

Like I said, if you find the time/money/energy!

Man that HMG seam looks beautiful, someone needs to figure out how to do that.

The seam looks like a flat felled seam that they then bonded an extra strip of cuben on top of (maybe also a layer below). You can barely make out two thin lines just inside the edges of the whiter strip, I'm assuming those are stitch lines. Dimensions are what, probably 1/2" flat fell seam and 1" cover?

BTW I really like the concept of that corner tieout from warbonnet. Not sure what the pros and cons of such a system are, but it definitely has potential. Forces the corner stresses onto the edges and eliminates the entire problem that this thread addresses. Of course you probably need a more aggressive caternary cut on the edges to get a small enough angle between the edges. That way it eliminates any buckling across the face and the forces pull more directly along the edge lines. Your photo shows some small buckling of the face due to the rather wide 90 degree angle.

The seam looks like a flat felled seam that they then bonded an extra strip of cuben on top of (maybe also a layer below). You can barely make out two thin lines just inside the edges of the whiter strip, I'm assuming those are stitch lines. Dimensions are what, probably 1/2" flat fell seam and 1" cover?

Pretty darn close. The middle part is indeed 1/2" wide but the cover is 1.25". It's hard to see what's really going on because there's a lot of layers of material, but there does not appear to be any stitching.

To me, the HMG seam looks to be like this, but it's hard to really tell for sure because there's so many layers:

The apparent problem with this depicted design is that the seam could come unrolled on the underside. Perhaps there is a line of stitching to prevent this that I can't see, or maybe I've just got it all wrong. As long as it doesn't come unrolled, a rolled seam seems like the strongest possible design and it could indeed be stronger than the fabric as HMG claims.

This doesn't clear up too much, but here's what HMG's site says:

HMG has had independent strength tests performed on a variety of cuben fiber bonding techniques including taping, stitching and a combination of the two. Based on these tests as well as our own field testing, it has been determined that the most appropriate technique depends on the application of the seam. For example, our tarp ridgeline seams involve a multi-step bonding process, with multiple tapes, creating a ridgeline that is stronger than the fabric itself. This allows the opportunity for a tightly pitched tarp capable to withstand high winds, or even snow. We also employ flat taped seams, stitched seams, and combination seams depending on the seam application, in order to produce the strongest products possible.

Actually that Warbonnet tie out method would seem to address the cuben tarp tie out failure that Steve Evans shared on another thread recently. Here is the thread …

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=38566&disable_pagination=1

Brandon Waddy over at Warbonnet is a pretty innovative guy! I own one of his wonderful hammocks.

It makes no sense to do a flat felled ridgeline seam with bonded cuben. By doing this you are creating a seam thats in peel rather then lap sheer. A simple lap seam is the best ridgeline seam you can make. I have tested a flat felled seam to a simple lap seam and the simple lap seam is much much stronger. Sure it looks boring and takes alot less time to do but who cares when it works… Adding a piece of tape to the top and bottom really makes things stronger but isn't necessary.

The tie-outs on my Warbonnet Edge in Spinn don't look like that. It's a 2010 model tarp. It's got more traditional reinforcement patches with 1" grosgrain and plastic triangles.

There are still some small loops of grosgrain(1/4") sewn into the box stitching of the aforementioned 1" grosgrain, that have the welded rings there, but I always assumed they were there to function towards trucker's hitching the guyouts.

I think that Warbonnet tie-out is brilliant. I have to give it some more thought. It seems that the Warbonnet corner might essentially force the taut edges of the tarp to serve as a "frame" which allows the anchor points for the material to be moved from the corners to the sides.

How small could the corner cut-outs be? It seems to me that at a certain lower limit of cut-out size, the Warbonnet corner would begin straining the material along the diagonal more and more (it would eventually behave mechanically like a conventional corner, with no cut-out).

If you poke a pinhole or make a tiny notch in a conventional corner, for example, you don't automatically get all of the benefit of the Warbonnet corner (alleviating diagonal strain).

Also, it seems to me that a piece of stretchy fabric (green in the figure below) in a conventional corner achieves the same effect as the Warbonnet corner (alleviating diagonal strain):

I guess my idea (to add diagonal reinforcing fibers) and the Warbonnet corner just come at the problem of diagonal strain from opposite directions. I sought to make the material able to withstand diagonal strain, and the Warbonnet corner just seeks to get rid of the diagonal strain. I think the folks at Warbonnet may have the better idea.

It also occurred to me that, in addition to alleviating diagonal strain, the Warbonnet corner addresses the separate problem of concentrating strain.

If the tarp material were isotropic (equal strength in every direction), like Tyvek, diagonal strain wouldn't be particularly concerning. It is as strong in that direction as in any other direction. But the tie out still concentrates the strain on a small area of material at the corner. The conventional provision for this is a reinforcement patch.

The Warbonnet corner is essentially the same, I think, as a tarp in which cordage running in the edge hem protrudes from corner cut outs:

The taut edge acts as a semi-rigid "frame" to which the tarp material is attached, like a cot. The strain on the tarp material is not concentrated at a corner, but spread out across all four edges of the panel (I guess this assumes a bit of cordage in the ridgeline, too). In a tarp with Warbonnet-style corners, it might not be necessary to add reinforcement patches anywhere.

I guess I've begun to use this thread as a personal MYOG sketchbook/journal. I apologize for the rash of consecutive posts.

One last thought: in complex tarp configurations other than the A-frame (low tetra, mountain house, etc.), in which the primary anchor points may not be the corners of the material, Warbonnet corners might not be any benefit, and in fact I can imagine a case in which they might contribute to limp ridgelines, flapping, and very undesirable kinds of strain.

Imagine a pitch in which the corner must be folded to give a new ridgeline along the diagonal (red line in figure), as in the low tetra and many other foul-weather pitches for ground tarps:

This would give a limp ridgeline and a great deal of strain on the edge of the material in the corner cut-out. We could modify the Warbonnet corner to provide for the complex pitch and diagonal ridgeline:

But then we just end up adding diagonal reinforcement, as I was doing when I started this thread. Also, some complex pitches create ridgelines that are not at 45 degrees to the edges, and a Warbonnet corner modified to account for this might require numerous extra lines of reinforcement.

Warbonnet corners are brilliant and beautifully simple, but it seems to me that they only offer advantages in an A-frame pitch. In light of this, I think they may be appropriate for hammock tarps or dedicated A-frame tarps (like cat-ridgeline tarps), but for pitch flexibility in flat tarps, I think the Warbonnet corner might not be suitable.

Since my project involves a flat tarp and I like complex pitches, I guess I'm back to the Vectran reinforcement.

The only problem I see with this design is that the panels make a 90 degree attachment to the metal ring (btw, would a heavy duty O-ring work to put in a small amount of stretch?).

Climbers know to make as tall of a triangle as possible when setting up an anchor because it distributes the load to the sides better. The same principal would apply here. With a 90 degree angle you just don't minimize the load applied to the tarp face. With 90 degrees the math works out to that for every lb of tension you apply to the guyline, ~1.4 lbs of force are applied to the tarp edges (.7 lbs to each edge). If you were to use a 45 degree angle between the edges of the tarp, you reduce the load to 1.08 lbs on the tarp (.54lbs to each edge).

In addition, the corner will tend to stretch in the direction of the stake and this will introduce a torque at the attachment point. With the method on the left of your image Colin, you need to to reinforce where the loops separate from the panel to ensure it doesn't tear. With the system on the right, you have to make sure your cord doesn't cut through the hem as it saws back and forth in a wind.

This is why I think a more aggressive caternary cut on the edges would be desirable for this tie out. It reduces the angles which minimizes forces to the tarp in general, and reduces any sideways pull on the edges.

about the same conclusion I came to on the warbonnet corner. Great and simple idea for a specific application. A lot of potential for other applications, but those possibilities are lateral steps from your original post, not really improvements.

The ring is also welded, if that matters. And yes, i will be using my tarp for a hammock setup.

Colin, keep posting your musings! All very helpful to the thought process. I too use my tarps over a hammock, so these corners work for me, but I can see your point about lack of versatility for a general purpose tarp.

But some good thoughts here. Did you end up building this Colin?
I'm working on a 4x4m tarp design (with A frame ends) and looking for join and tie out ideas to deal with the larger size (and greater stresses) than what iv'e done before.

I like the butted (sandwich) seam but your diagonals incorporated into a WB style tie out have me interested.