Polycro Tarp Tested!

[Mike Oxford]

I wonder if Tyvek Homewrap strips would be better for mounting the washers than the tape .

[Michael Ray]

Frankly, if it doesn't hold now, I'll just go back to my loops of tape. They don't look as elegant, but they worked. I will theorize it failed because I folded the tape right against the washer rather than leaving some space on the side where the force is applied. When I added my reinforcement layer, I did it that way, leaving maybe 1/8". I think I may try a subjective test of tieout design. I wish I had a fish scale.

As it turns out, the training I drove over 90 minutes to attend was canceled and they failed to notify me. Grrr. So I pitched in the backyard again, purposely the wrong direction so it should pop open like a parachute. Supposed to have some decent winds and gusts Sunday.

[Michael Ray]

I wish I had a fish scale or similar to make this more objective, but I played around with some different tape combinations to see how much force it would take for them to fail.

You can see that only 2 had not failed at the point I decided the pain in my hand of pulling on the Triptease (didn't use a glove or wrap it around a rod) was likely more force than it would normally take. I'm sure it was over 40 pounds. Interestingly the one I judge the best was just the tape loop (2nd from L) I'd been using all along. I normally use half that width (far L) so it doesn't bunch as much, but I also normally make it with 8959, which is stronger than 2120, and then cover it with 2120 for UV protection. The far left was just a single layer of 2120. The loops are technically double layer to prevent sticking, but only a single layer contacts the material.

The second best (6th from L) was what I have on my tarp now after the failure from the other day – one loop butted against the washer and a second layer that leaves 3/16-1/4" on the force side of the washer.

The worst one was how I started – one loop butted against the washer (3rd from L). It was pretty much tied with a single loop that left 3/16-1/4" on the force side (5th from L). Next came 2 loops butted against the washer (4th from L). Finally, the GG tape took a bit more force (maybe another 10 pounds?) to compromise. Both were pretty similar on whether the loop was butted against the washer or left a gap.

[Michael Ray]

Video added
Notice my comment, too. :)

[Donald Krug]

Thanks for the video. Now I see what you are (were?) doing with the washers. I made a tarp of this material for hanging over my hammock. I only had it out for testing once and there was very little wind. I will try to get it out for more testing soon.

I saw your comments about the failure and am wondering just how much stress this will take. I'll let you know if I learn anything in my testing.

[Michael Ray]

I'm pretty sure the corner that had originally failed before the video (see further up this thread) went first. I discovered I'd repaired it with only a single layer with a gap (5th from L in the pic) so it was one of the weakest designs. Even so, it took some pretty serious gusts before it went.

Once that went, I bet the peak went since I'd butted the washer against those pieces of tape and it had also been pulling out from the backside as you could see in the video.

If you look at the short followup video, you can see I fixed the angle issue at the peak with a larger ID. At this point I've decided to stick with the washers rather than replace all the tieouts with loops of tape. I may go back to loops with Prototype #3 if I have any more issues, but I think I've learned enough now to know how to make the washers work. I definitely like a washer for the pole connection (similar to the grommets on my Lunar Duo).

Others have suggested placing the washers within the hem itself for a cleaner look like a generic blue tarp with grommets. I believe the reinforcing tape would need to be different in that case. For one, the washer would only be captured by it on one side (sandwiched against the polycryo). Knowing tape doesn't stick as well to it, I think it would be easier for the washer to slide under force. Thus, I'd be wrapping at least a couple layers of tape around the edge of the hem to stop the washer once it made it that far. I'd likely put it very near the edge to start though since if it does slide the polycryo would then have a small tear in it. That's just my expectation though. I haven't tested it and don't plan to as I prefer my method.

[Daryl and Daryl]

Michael,

Thanks for all your experimenting and sharing. Very helpful.

Daryl

[Ultra Magnus]

I've been thinking about this and maybe round washers are not the hot ticket. Your tape folds over the washer, and the edge of the washer concentrates the load at that middle point of the folded over tape- a point load, if you will. What might work better would be a rectangular washer. Take some kind of semi rigid plastic, maybe a section from a milk jug or something similar, cut out a square the that matches the width of your tape, and sandwich that in your loop of tape. Maybe fold the plastic piece in half, doubling its thickness… I dunno- just thinking out loud. But either way, the straight edge of the plastic reinforcement would spread the load across the whole width of the tape, and you'd have more area of adhesion between the tape of the reinforcement increase the amount of load carried in shear.

I'm better at coming up with ideas than I am at explaining them, but I hope that makes some sense.

BM

[Michael Ray]

You are correct that that would help. Perhaps buying some larger OD washers and grinding off one side would be a simple solution. I don't think a milk jug even doubled over would be stout enough. The plastic should be harder.

[Michael Ray]

I have a little data to share now on the tieout failure tests since I was able to borrow a cheap fish scale.

The worst case started deforming around 10 pounds and busted in the 15 range. The best of the ones I had done previously managed about 40 before breaking on a single attempt but repeated pulls to 30-35 would eventually cause it to go.

I did a few other combinations. I doubled up some GG and it held to the 50 lb max of the scale. I doubled up the loop and it held repeatedly at 40-45 but gave out at 50.

Then I made a single loop of the 3M 8959 that I had used on my previous tarp and it held 50 repeatedly. I suspect it would also fair better using washers since it's essentially high-grade strapping tape.

So what would I do different knowing this? Prototype #3 will likely go back to using 8959 for the actual connection point of the tieouts. However, it must be covered with 2120 to provide UV protection or it will disintegrate like normal strapping tape. GG could be used but it is not as strong as 8959, is heavier and it just doesn't look as nice. :) Maybe I shouldn't be so vain. LOL

While it's difficult to determine just how well the forces are distributed via the tieouts, you can at least guess that if you can accommodate at least a 3" section that it would take at least 25 lbs to break the tarp material based on the thread we had a couple months ago. So if my tieouts don't break until 50+ lbs, I shouldn't have to worry. Ryan's Storm Resistance article (when will Part 2 ever come out???) says, "Generally, moderately stormy conditions (snowfall equivalents of several inches through a night, or wind loads induced by 30-40 mph / 48-64 kph winds) can transfer up to about 40 pounds (18 kg) of tension force to guylines and stake-out points for most solo shelters." So I should be good to go there, but the article also states, "a significant mode of failure of ultralight shelters, especially those that employ low-stretch fabrics such as Cuben Fiber, is the shelter’s inability to be staked out tightly at high enough loads that induce a good distribution of tension evenly across all fabric panels. (emphasis added)" I think the saving grace here will be that the material does have a little give.

As an aside, one other point that I noted in the video but not here – the "catfish dropline" I got at Walmart held repeatedly at 50 so it would be suitable for some guylines. I don't know if it would work with linelocs or hitches though as I just tie a bowline on each end. But it's cheap, lightweight, braided nylon twine.

[Kevin Beeden]

As UM suggests, a round washer will tend to concentrate stress at the radial edge.

I considered making a simple reinforcement by taking a piece of PET bottle wall, folding it in half, and then punching a hole in the centre. You might even use a hot tool to melt the edges of this hole to soften & thicken the edges. PET bottle wall is pretty strong (I made some nice mudguards for my MTB that lasted until it got stolen…).

If the sharp edge of the PET is an issue, you could fold the PET around a round washer, allowing the straight, folded edge of the PET to act as a load spreader for the washer.

Since we've put a piece of folded PET inside a loop of tape, we have the choice of using the punched hole, or simply threading the guy through this PET loop. Again, the sharp edges might prove a problem, but some careful manipulation of the PET with a heat source might allow us to add a curved shape to it.

[Michael Ray]

> you could fold the PET around a round washer, allowing the straight, folded edge of the PET to act as a load spreader for the washer.

That would help.

> Since we've put a piece of folded PET inside a loop of tape, we have the choice of using the punched hole, or simply threading the guy through this PET loop.

Actually if using simply a loop of tape like I've done in the past, it doesn't give right where the guyline passes through as you might expect so the PET would be pointless in that case.

Yesterday morning I was concerned this material was going to condense really badly because it was soaked on the inside. I thought that was odd since the previous days I hadn't noticed hardly any. So I put up my LDPE shelter next to it since I'd rarely had a condensation issue with it. This morning there was still significant condensation but not as bad and it was fairly similar in both shelters so I was happy to see that. Here's a shot of my original shelter and it's slightly larger younger sibling.

[Kevin Beeden]

> Actually if using simply a loop of tape like I've done in the past, it doesn't give right where the guyline passes through as you might expect so the PET would be pointless in that case.

Yes, I'd expect the tape to simply bunch together, spreading the load over the entire width of the tape, even if the loading at the contact with the tarp body becomes a little non-uniform as a result.

My comment assumed that the PET had been put on the loop anyway. So, if it's there…

[Matthew Eng]

So, what's the best way to construct tie-outs on a tarp like this? I'm making one out of 3-mil Polyethylene. I like the idea of grommets on tape-reinforced areas, but would making loops be better for side tie-outs in case you wanted to stake it all the way to the ground?

[Michael Ray]

You could run a stake through the grommets to take it to the ground (assuming you're using nail/hook stakes). I normally use bowline knots so have a smaller loop of line around the grommet that I use with my Y-stakes if I want it close to the ground.

As for the best way, read through all the above and note the ones that clearly didn't work as well as others. :) I haven't tested every way either, of course (like embedding the "grommets" in the hem).

BTW, since polyethylene stretches so much you'll need to reinforce any ridgelines with 3M 2120 Transparent Duct Tape (also known as L520 I think it is). I did it with the polycryo as well, but it's not as necessary there (I'd still recommend it though unless you're going for not as long life and light as possible). You can see exactly what I mean if you watch my videos on my tarps (search the channel for myog).

[Will Webster]

Has anyone tried doing this with space blanket material? I'm thInking about putting together an emergency bivouac kit for winter dayhiking, and if can stand up to the service the reflectivity might be worth the noise.

[Alex W]

a shelter with a space blanket http://www.youtube.com/watch?v=QatcuLnqnhQ&feature=plcp

[Michael Ray]

> Has anyone tried doing this with space blanket material?

Technically, my first one (shown in my avatar as well) was since it's aluminized, but it's LDPE rather than mylar. The original designer I got the idea from did use mylar but was concerned it wouldn't hold up to hail at Philmont so switched to LDPE for that trip. Mylar will catastrophically fail whereas LDPE will not. LDPE is also not as noisy.

[Jim Colten]

Has anyone tried doing this with space blanket material?

Hi Will,

Checkout this thread

[Matthew Eng]

Home Depot didn't have the 2120, I ended up using what turns out to be non-UV resistant packing tape :( We'll see how long it lasts, and if it's worth repairing. I think I see silnylon in my future…

I'm a newbie to tarp camping, and just made my own hammock and bug net to boot. Thanks for all the great info on this site!

[Angus A.]

Here's a straight to the point video of a space blanket tarp.

[Douglas Frick]

I've been using a fairly big (10ft x 12ft) 3-mil poly tarp with the kids this summer, and it has worked well. Not exactly UL, though. I have an extra GG Polycryo ground sheet, so I think I'll do a bit of experimentation.

There are two things I'd like to try, and if anybody has already, I'd appreciate your input. The first is to attach the corner guys with a sheet bend, Ray Jardine-style. This has worked well with my poly tarp.

The second is to use Dow WeatherMate Construction Tape (like DuPont Tyvek Tape) for the hem and tape loops. It's UL, waterproof, strong, and very sticky.

[Michael Ray]

> The first is to attach the corner guys with a sheet bend, Ray Jardine-style.

I'm surprised it distributes the force better but if it works for you, go for it. I'd think it would cause more flapping in the wind, too. Personally, when I do corners I add tape that goes perpendicular across my tieout to spread the force over the whole corner (and hold the tieout better).

> The second is to use Dow WeatherMate Construction Tape (like DuPont Tyvek Tape) for the hem and tape loops. It's UL, waterproof, strong, and very sticky.

This sounds like an intriguing alternative to the Transparent Duct Tape. Can you typically find it in big box stores and how much is it?

[Douglas Frick]

>> The second is to use Dow WeatherMate Construction Tape (like DuPont Tyvek Tape) for the hem and tape loops. It's UL, waterproof, strong, and very sticky.

>This sounds like an intriguing alternative to the Transparent Duct Tape. Can you typically find it in big box stores and how much is it?

I can't find where I bought it, now, but it's available on Amazon for $15 (1 7/8 in x 55 yd); it's a special order item at Home Depot. I bought it for making a bivy out of #14 Tyvek (6.8 oz; oversized). The entire roll weighs about 7 oz.

For this application, Scotch-brand clear packaging tape might work as well; it's certainly cheaper.

[Michael Ray]

> Scotch-brand clear packaging tape might work as well; it's certainly cheaper.

Maybe to hold the tieout, but not for the loop. It's also not UV resistant.

Please report here your findings on how well the Dow tape does in your tests.

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