I’m working on a tarp-poncho made out of silpoly 1.1oz PU4000. Knowing that one of the weakness of this fabric is its tear strength (The trade-off is a much higher aged HH rating of 3500+ which is very important for me when used in Poncho mode) I have done some catastrophic failure tests for tie-outs (for when it will used in tarp mode).
I found that rolling the hem over twice and sewing the tieout produce failure at 25 lbs.
When I reinforced the tie out section by gluing a reinforcementt patch up of the same fabric (with the ripstop grid layered in the same direction of the main fabric) and rolled over (twice main fabric, once patch, so 5 layers of fabric at stitch line). The tieout failed at at the stitch line at 40 lbs.
In this post David Gardner, a fellow BPL member, mentions that he measured 25lb of tension at the ridge of his tarp. He stated that he pulled on the guy-lines tighter than he normally does but still I assume this is just under regular conditions. I have pitched my tarps under strong winds and when pulling the guyline did certainly felt less tension than when I was pulling the 40lbs in the test mentioned above.
My question is how much tension is reasonable to expect on a small tarp (5×9) assuming the whole panel is exposed to the wind? (i.e in lean-to configuration).
