I have just used whatever the cord was that came with the tarp - but I do modify it just a little.  I remember reading somebody's post about eyelets ripping out of tarps if there was no give.  So what I've done is remove all the cord, then tie a small loop of elastic shoelace onto the eyelet, and then tie the cord to the elastic loop.  (That shoelace stuff won't last forever, I'll have to keep an eye on it.)   I can draw them pretty tight, but it provides just a little give.  I know this doesn't quite answer your question though.

One thing that might be happening is if you are going around a tree with a tarp line, it may not be stretching so much as spinning a little bit on the tree as it seeks its' "center" position.

Still doesn't answer your question of course - but I'm sure somebody here has an answer for you!

I camp with tarp and bug bivy only, love this set-up.

CCS tarps are awesome. Zpacks has tarps made of crazy new UL  fabric with no stretch... but too expensive for now. Any silnylon tarp will stretch in the rain - the ridgeline, however, should not stretch.

Amsteel is great stuff for a ridge line. I use 7/64". Something ridiculous like 1500lb strength, very light and does not stretch. A bit slippery, but great for ridge.

Ridge goes through the loops on the tarp, does not actually attach to the tarp. Siberian hitch on one side, trucker's hitch on the other.

Utility cord for all else. 2mm works well, 3 mm is too thick. Prussik knots on the end loops either side to keep the tarp taut. I carry 6 guy lines and 4 stakes.

Hoop from wintertrekking.com has a good video and discussion:
http://www.myccr.com/phpBB3_PROD/viewtopic.php?t=44404&p=405784

Amsteel cord:
https://www.marineoutfitters.ca/index.cfm?category=10045|10551&product=45763667&code=Rope%20764%20Amsteel%20Blue

Utility cord (scroll down) from Ray Jardine (I really like diy, this guy is the father of ultralight). Ray also has a book about tarps, it's pretty good.
http://www.rayjardine.com/ray-way/OrderForm.php

Just in car now driving back from Ottawa, can post some pics with tarp set-up later...

Cheers
Marko

Last edited by Marko_Mrko (5/14/2018 11:18 am)

Prusiks are key to keeping the ridgeline tight. Tautline hitch for the guy lines at corners.
https://www.netknots.com/rope_knots/prusik-knot
https://www.netknots.com/rope_knots/tautline-hitch

Biners at the ends, that allows me to pitch the tarp lower.


One side has the last two loops on biners - that allows an even lower pitch:


Low and tight for storms. Awareness of wind direction is pretty important...


M

 

Last edited by Marko_Mrko (5/14/2018 12:11 pm)

We use a ridgeline and appropriate prussik knots and sometimes do the centre to pull it into a pyramid. The big issue has been the cordage we've tried. We really like reflective cord (ya know, to avoid clotheslining yourself at night) but even things that say they aren't supposed to stretch end up stretched.

Sounds like some good suggestions here for different types of cord to try; we'll check it out. Thanks!

Another vote for Dynaglide and its big brother Amsteel. 

If your tarp is made of sil-nylon, it will sag a bit as it gets damp or or wet. I just got a sil-poly tarp, and it didn't sag on me at all. 

I believe that nylon is stronger than polyester.   Weight is extremely important if my wife at the age of 63 and myself at the age of 60 are going to be able to continue to single pass portage.  We use a MEC Scout tarp which is a silicone coated nylon tarp and lengths of the thinnest nylon static line (2mm?) I could get at MEC tied to the center and corners of the tarp.  Both the tarp and cords stretch after I have set it up but I'd rather spend a few minutes tightening the cords now and then than having to carry a heavier, bulkier tarp.