DIY OutdoorINK Sil-Poly Hex Tarp with Grosgrain RL/Edges ("Starry Night")

[kitsapcowboy]

I decided to build this tarp as a gift for my wife, something of an early Mother's Day present.

This tarp was a "proto-tarp", a test-bed for me to try out some construction methods that were new (to me), and a chance to make something out of material from the pre-launch run of Ripstop by the Roll OutdoorINK 1.1 oz sil-poly, their first digitally printed waterproof outdoor fabric. I've always liked Van Gogh's "Starry Night", so this rendition spoke to me.

A special shout out to jellyfish and her quant sister for the recent contribution of a 1:12 true catenary curve calculator spreadsheet.

Here was my result...





The basic design for the tarp is pretty standard for a full-width cat-cut hex tarp with an 11-foot (132") ridge line and a 114" finished width; I've built them before using the dimensions of the much-copied free pattern at DIYGearSupply.

I made three significant departures from the online construction method:

1) True Catenary Curve with 1:12 Aspect Ratio -- I used jellyfish's calculator to plot a true catenary curve with significantly deeper deflection than I normally use for the ground edges, 6" deep on a 72" curve instead of my usual 4" to 5", as I wanted to see if a more aggressive cat-cut would be significantly more difficult to sew and whether it would yield noticeable improvements in performance. (The 67" wide end cat-cuts are a much more shallow 3" in depth.)

2) 1.5" Grosgrain Reinforcement on Standing Seam Ridge Line -- I've used this method of folding polyester grosgrain ribbon over a standing (French) seam at the ridge line before to provide increased strength and water resistance, and it has worked very well every time. It is not specified in the DIYGS plan, and it adds about 40 grams to the tarp build (less the weight of any seam sealer and shorter grosgrain tie-outs you would have used following the standard method).

3) 7/8" Grosgrain Folded Edges -- My most radical new technique to test was sewing folded 7/8" grosgrain ribbon over the 1/4" rolled hems on all the lateral edges of the tarp panels. These grosgrain reinforcements tied directly into sil-poly reinforcement patches at all vertices. I also tried a new tie-out method, sewing looped 1/2" grosgrain ribbon inline with the folded edge binding to create a UGQ-style "zero-stress" attachment point for guy lines. The ends of the folded grosgrain tarp edges were fully encompassed within the wider grosgrain reinforcement at the ridge line, bar-tacked to it for maximum strength at this critical juncture. The entire grosgrain perimeter reinforcement added about 60 grams to the build.



Total weight of the tarp (with four looped LineLoc 3 adjusters added on) was 13.8 ounces. Total build time was about a day (8 hours).

Construction details, "action photos" from the build, and performance notes to come. Thanks for reading this project report...