Tarp Ridgeline Issue
I am having a sagging tarp issue.
Currently, my wife and I are hiking the AT and are hammocking. We use a cuben tarps that we made, and based on some comments elsewhere on the forum, are using a continuous ridgeline so we do not put un-needed stress on the cuben's ridgeline seam. We use prussik knots with a small carabiner to hook to the D Ring on our tarp ridgeline.
This has worked well while using the Zpacks zline spectra cord (http://www.zpacks.com/large_image.sh...rd/zline_l.jpg). This is great cord in general, although we have had it start to break down using the DutchBones as this cord is not a braided, but a core-with-sleeve design.
The issue has started when I went to using the ZingIt. I like this cord a lot, but my prussiks slip, even when I have a 5 loop prussik. Any ideas on how I can solve this? I am currently using a Sterling rope for the prussiks.
An additional footnote...I have used shockcord for the prussik knot as well, and do not want to use it again. The stretch that it makes requires a longer distance between the two 'Vs' that end up requiring the tarp to be set too high.
Swap out your present prussik loops for ones made from zing-it (the same as your ridgeline) and try a four wrap with the new ones.
Zing-it is slick and needs a little break in time, I wrap my prussiks and slide them along the ridgeline cord to wear away some of the coating.
Generally prussiks like to be a smaller diameter than the main line (climbing, human support, etc.) but in our application of tarp support, the same diameter works fine.
Yep like gargoyle said, use the same line for the prussicks. Thats what Arrowhead Equip and Whoopie Slings.com does. Works great.
More wraps help, as Gargolye points out.
Originally Posted by Chop
Something else worth trying is a different knot. The prusik by symmetry offers resistance from both directions of pull. Something like the Kleimheist (also used by climbers) is uni-directional, and in my experience works well in this context.
You do normally put the tarp *over* the CRL, don't you? Or am I missing something?
Its a matter of preference. Some like it on top, some like it under.
Originally Posted by nothermark
I prefer the ridgeline under the tarp. Bears some of the tension along the entire length of fabric. Provides a handy clothes line for hang gear or drying clothes.
Some say they had leak issues with an under the tarp ridgeline (I have not) So they prefer an over the top ridgeline.
+1. This knot solved my prussik slipping issue, and is very easy to tie.
Originally Posted by GrizzlyAdams
On disappointment with the prusik:
I believe the design of the knot is for a smaller cord to grab and grip a larger one. Prusiks don't work as prusiks unless there is a difference in cord size. Worse, you are trying to make the knot work the other way around
I have not had a line-lok in hand. Is there a reason, other than aesthetics, not to use one in this application? Or a cord lock?
I am surprised to read that the dacron sleeve on z-line is not doing what it is designed for on larger cord for arborist and maritime industries.Maybe, at small weight penalty, you want in the future to use a continuous loop for the ridgeline. That way you can distribute the wear almost forever.
In your photo, I assume that the blue material is a reinforcing patch sewn or bonded to the cuben, which is out of sight. I have found with my cuben tarp that having the ridgeline above the tarp, as in your picture, allows a narrow trough to form at the ridgeline where water can pool up. Because I beat up my tarp, taping silver mylar to it at the beach and other abuses, there was a tiny pinhole in the polyester laminate near the ridge seam that allowed water to drip through gradually. This only happened when water was pooled in the ridge trough. I put the ridgeline under the tarp, and the problem was solved because it held up the center if the ridge so there was no concave area for water to collect. (I also subsequently put 1" square patches of DIY cuben tape on both sides of the pinhole, which really fixed the problem.)
I'm not sure why the trough formed in the first place, because it suggests that the bonded ridge seam was stretching, relative to the single layer cuben material on either side of it, which seems counter-intuitive. That's what would happen with a silnylon tarp that didn't have a catenary cut on the ridge. It's also possible (though not likely) that the two edges of cuben that I bonded were not perfectly straight. Who knows? Anyway, my problem is solved. On to yours:
I use a three part zing-it ridgeline with loops of 3/16" bungee to attach the tarp to fixed points where the middle part connects to the two ends. That assures that the tension on the tarp ridge tie-outs is mostly limited to the pull exerted by the bungee loops. That means the tarp can't slide on the ridgeline, so adjustment between the trees is done with the TarpFlyz on each of the two end sections. I'm not suggesting that you switch to this arrangement, as the advice you've received on prussic ropes may solve your problem, but it's another option, should you need it. I'm not clear on the problem with the tarp being too high when you tried bungees for prussic ropes. Was it the tarp itself that was too high, or did it necessitate tying the tarp ropes higher on the trees? I'd expect the tarp ropes to be tied lower than the hammock ropes generally, and the tarp height to be set by where you tie to the tree.
I've only addressed your present problem with a back-up solution, but maybe I can help with possible future problems. If you PM me an address I'll send you some of my DIY cuben repair tape for field repairs. It weighs next to nothing. (You can, of course do emergency repairs with other tapes, but be warned: when you remove packing tape or Gorilla tape from your tarp, you risk pulling part of the polyester laminate with it. That's how I got the pinhole in mine.)
One final question - in the photo there's an oval black connection between the carabiner and the tie-out webbing. Is that a heavy O-ring? If so, good idea!
Have a good hike!
+1 on that.
Originally Posted by gargoyle