One of the popular fabrics for making lightweight tarps and shelters is silicon-impregnate ripstop nylon—silnylon or ’sil’ for short. It is valued for its light weight, strength, and waterproofness (and relative low cost compared with other options). But like all nylon-based materials, it has a downfall: it stretches when it gets wet. And it’s not just rain—a light dew or a rolling fog can render a silnylon shelter a little saggy, and if your guy line is also nylon-based, you have a compounded stretch effect. Regardless of the shelter style or design, if you pitch a sil-based shelter taut before bed, you may wake up with some sag.
A sagging tarp can be less effective in a heavy downpour (depending on the style, construction, and shelter set-up), resulting in pooling water on the outside (or worse), and undulations in the stretched fabric can create low points for accumulated condensation to begin dripping down on you from inside.
One way to help reduce stretching and keep a shelter taut all night is to install a piece of shock cord inline with the guyline to create self-tensioning pull-outs. While there are some manufacturers who retail self-tensioning guylines, it is pretty easy to make them yourself with a little piece of shock cord and a simple knot.
Materials Needed for 1 Self-Tensioning Guyline
- 12 in (30.5 cm) of 1/8 or 3/32 in (3.175 or 2.5 mm) elastic shock cord
Getting it all Set-up
NOTE: You do not need to remove your guyline to make this work. In fact, your guyline should be tied to your shelter. In this way, if the shock cord were to unexpectedly break or otherwise come off, your guyline would still be attached to your shelter.
1. Feed the shock cord through the guy point (tie-out, ribbon, D-ring, etc.) on your tarp and bring the two ends together.
2. Pull and stretch out the shock cord along the guyline to its maximum stretch point.
3. Mark this point on the guyline.
4. Where the mark is, tie a Clove Hitch with the guyline around the two ends of the shock cord, securing the line to the shock cord.
An alternate method turns the shock cord into a continuos loop by tying the two ends together with a Fisherman’s knot. Join the shock cord to the tie-out with a Lark’s Head knot and follow the process to stretch and mark the guyline. At the marked point, tie a Becket Hitch around the shock cord.
When the shock cord is relaxed, you should see the guyline hanging loose between the guy point and where the shock cord is tied off.
When you pitch your tarp, pull the shock cord tight and set your stake or anchor point.
During the night, as the silnylon stretches, the elastic will take up the slack, keeping the fabric taut.
The shock cord serves a second purpose: providing some flexibility and stress relief on the shelter in high winds, helping prevent rips and tears. This is useful for sil and non-sil shelters alike.
You can always shorten or double-up the shock cord for short guylines (or for more tension).
Former Trail Ambassador Derek Hansen is the author and illustrator of The Ultimate Hang: An Illustrated Guide to Hammock Camping.