Tarp Catenary Cut Hex, Rolled hem too stretchy vs grosgrain?

[C_Claycomb]

Got my fourth tarp project started and am going to use catenary curves, material is SilPoly, starting with 1.6oz, then got another project with 1.1oz. Tried doing curves once before and found it easiest to a roll the hem by hand around a 10mm piece of grosgrain. The resulting hem had very little stretch. That tarp project was a bust for other reasons.

I am now better at using my 1/4 inch double rolled hem foot and just did a test curved hem, 1.6oz, 67" long, bias, about 3.5" cut in. Hem doesn't look bad, BUT it stretches like rubber, 5 to 6 inches over that length.

It seems to me that two hex tarps of identical design, one with rolled hems all around, and one with grosgrain reinforced hems, cannot possibly behave the same way for pitching. If the purpose of the cat-cut is to straighten out and put more tension on the middle of the panel, which is better, high stretch or low stretch hems? My gut is going with the latter, but advice here is split. All the threads I have read only talk about the difference in difficulty of sewing rolled hems on curves, nothing about whether the stretch of the finished hem is more or less desirable.

I have read at least one thread where a guy had found that his silpoly tarp became flappier over time, with the edges stretching. His hems were just double rolled.

Has anyone used both and noticed a difference?

Thanks

Chris

[C_Claycomb]

Hmmm...maybe I spoke too soon,
https://www.hammockforums.net/forum/...=1#post1779520

Suggests that the grosgrain perimeter is too stiff and does not allow the centre to tension....

[LooseGooseDownSupply]

Warbonnet does grosgrain along the entire edge and it always pulls tight. I think that either way you do it you will be fine.

[NeighborhoodNinja]

Warbonnet Superfly without grosgrain along the perimeter and with grosgrain along the Ridgeline. Ive not had any issues.

IMG_0855.jpg

[C_Claycomb]

Well, I did my 1.1oz Silpoly Hex with 2.5" cat cuts on the ends and 4" along the bottom. The ends started out around 3" but some of that has vanished in the finishing. Rolled hems throughout using a 6mm rolled hem foot. A little wobbly in places and puckered, but I didn't think they were bad....until I pitched for the first time.

Only one of the four bias ends gets tight. The other three look okay, until you check the tension and find than they are just floppy and sitting there. Cannot figure out what is different on that one hem.

Floppy tarp ends by Last Scratch, on Flickr
(no, your eyes are not playing tricks, one end is pointier than the other. I had 7 yards and wanted to get a 142" ridge and 82" side)


IMG_4298 by Last Scratch, on Flickr


I did try sewing 6mm grosgrain into the seam, by rolling the fabric around it, which had worked for making a neat rolled hem on another project, but this time it was a total disaster, the catenary curve fully reversed and instead of having a concave edge, the edge bowed out, convex! Luckily I was testing on scrap! Tried it three different ways, same result every time.

Yeah, I am sure it will keep most of the rain off....but I was aiming for something that would pitch tight and this doesn't.