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Roger,
Agree with your ‘just thoughts.’ That is why I spent so much time looking for micro or mini ripstop grids in lighter tent/tarp fabrics. Am pretty sure I may have found one in silpoly, but the source is mum, although they have sold me fabrics in the past. I have some in silnylon that tested well with Richard, so will be testing it for sagging when tightened over a frame that creates a bias stretch. If that mostly eliminates the sagging that normally occurs in damp and colder weather, it may provide a partial solution.Re: “But I think we would be better served by a dynamic test that simulated raindrop impacts on a tensioned piece of fabric …”
Theoretically, if the static HH is great than 1500 (? – I forget the exact number) then you should be good. The dynamic force of a raindrop is less than that.
Annecdotal experiences-
When I was a young Boy Scout we often had SERE instructors visit our campouts and give us survival training. Their course area overlapped our campout area and we first met them when a couple of trainees tried to trade a lensatic compass for a ham sandwich. We worked with parachutes which were an uncoated 30 denier fabric. Set up as a horizontal tarp they sucked big time and were only good for a bit of shade or light snow. I got soaked. Set up as a steep single layer pyramid they would get a tiny mist in heavy rain. In those conditions a person’s body heat would offset the small amount of moisture the cotton sleeping bag covers would absorb. I didn’t get a chance to experience that, having set up the crappy low angle pitch. The instructors said that for a night in an emergency situation a steep pitch pyramid you would be good to go, but on successive nights you need a better shelter as the moisture on the sleeping bag surface would build up when you weren’t inside. Some versions of their shelters involved adding a waterproof poncho to one side of the pyramid for a dry side.
Shelters they made of two layers of breathable nylon, in rain and heavy wet snow that had been up for several days, were dry. We also used a giant tarp made from a whole parachute with a center pole cut from a small tree. A fire in the center kept out moisture from the heavy wet rain-on-snow event. It was great, we would head out and dig practice snow caves in the slop, then return and dry out by the fire.
What I came away with-
Pitch angle of the fabric makes a big difference in water penetration from rain or wet snow.
Heat differential makes a difference if the fabric is breathable both for shelter and sleeping system.
Uncoated fabric in layers can work in certain circumstances.
30 denier uncoated fabric is plenty tough for heavy snow conditions even when the tie outs are a cord clove hitched around a fir cone.
Agree with Oware. With the two of us in our double-skin tunnel tent, the inner uncoated fabric layer is often fairly dry if conditions are not too cold. Just a little bit of warmth.
Of course, if it is really cold, there may be frost on the outer surface of the uncoated fabric, but thems the breaks.
Cheers
Oware: At one time there was a company that sold tarps with only DWR for camping use. Think it may have been Brooks Range Mountain Equipment, but they are no longer, so could not check. Recall that the site seemed quite confident that the tarps would serve in the rain without additional coatings.
Jerry: Just to let you know that I’ve ordered a couple yards of the Membrane silpoly for testing. Will update after seeing if I think RBTR has improved the material over what I ordered around 2016. Will subject the current fabric to the same tests used on the old stuff. It will take some time to see if pinholes in the fabric expand or worse when the fabric is subjected to pressure for a substantial period of time, with the pressure being similar to what a tautly pitched tent would undergo.
It would be nice if the current fabric performs better, and would show that Roger’s confidence in ungridded fabrics applies to to the lightest silpoly, around 0.9 oz/yd2.
The day finally came when we got alternating drizzle and waterlogged snow, perfect to see what would happen to a prototype that relies on poles and canopy to mutually reinforce each other. ‘The fabric is a 30D silnylon bought from Quest before we had a long streak of not so good silnylon, and was tested well by Roger Caffin. Here again is a photo for clarity:
The prototype is normally quite stable and rigid. It was placed under a deck over a walkout basement, so had some protection but not much, and left outside for around 12 hours, An eleven inch dia. plastic embroidery loop holding some silnylon with PU coated on one side, was placed vertically next to it to use for comparison.
After a few hours, as was hoped the canopy did not sag, or even wrinkle; while the silnylon in the embroidery loop became so wrinkled it could be pushed about 3/4″ out of place at the center of the loop without resistance. However, the fabric on the canopy became much more elastic, and totally failed to keep the prototype stable and rigid. Were there a high wind, I could easily see the canopy being smashed almost flat without guylines, and even with them, becoming totally unlivable due to shaking and swaying, or breakage of the carbon poles without support from the fabric. The fabric was completely soaked.
So at this point, I’ve become an nonbeliever in silnylon, although I can see how it works for a highly tensioned and guyed out tunnel tent, like the ones from Roger, Warmlite and Macpac. The current membrane 15D silpoly has been received from RBTR, and will begin tests with the next deluge.. Will use the embroidery loops and larger scale models. And may see if an HH test can be obtained.
If the membrane silpoly holds a model canopy rigid in a storm, passes HH testing after simulated aging, and resists pin pricks and abrasion, will use it for all but a breathable inner ceiling on a tent. If not, will try the RBTR 20D silpoly, and live with the added weight. Thanks to Jerry for sharing his experience with his MYOG silpoly tent. I’ll keep you all posted.
I wonder if a lower denier nylon would do better in the wet than a higher denier nylon, as the thread are smaller diameter and so may absorb less water weight
I am hoping to get some of the MTN silnylon to make a bit of a pocket tarp to go with my A-frame mesh tent I have. I don’t think a smaller tarp will suffer much compared to a larger tent canopy, but it is interesting to think about.
Hi Michael,
When RBTR first came out with the MTN 6.6 silnylon, I bought some in dark olive for a tent floor due to its superior strength and durability, plus water resistance. I still intend to use it for a floor, and since sagging is much less a problem for a floor, have not tested it for sagging. Granted, others use the silpoly for floors as well, to prevent slipping around. For a floor, I’m more concerned about durability and strength.
However, I want a tent with a canopy that will stand firm in foul weather, and as noted in my above post, I no longer think silnylon will do that well.
From tests of silnylons on BPL, I don’t think a lighter silnylon would be any more waterproof, and that it is the quality of the coating that counts the most. Note that recent HH tests of 20D silpoly by Stephen Seeber have run at least 2700mm after simulated aging, or well above the 1500mm standard for waterproofing.
Note that the MTN silnylon is even heavier than the 20D RBTR silpoly, so it won’t save you any weight. I do think that any silnylon will expand in wet weather, or just colder weather that brings dew into the picture. So even on a tarp, the guylines will loosen as it expands. Moving about in a tent or tarp trying to tighten guylines in the middle of the night in bad weather is just what I’m trying to avoid. Sleeping soundly in a good protective shelter is my goal.
Granted, I’ve been pretty lucky in the past with nylon shelters, but most of them had heavy PU coatings, heavy poles, and were anything but superlight.
Note that the MTN silnylon is even heavier than the 20D RBTR silpoly, so it won’t save you any weight.
MTN 7D silnylon is .77OSY, and Membrane 15D Silpoly is .93OSY, so 18% savings. I agree it is not much of a savings for a small tarp, But I assumed it would take more tension to offset any sagging compared to the Membrane.
I wasn’t really suggesting a low-denier nylon would be more waterproof – as you say, that is more a function of the coating. I was merely suggesting that maybe due to the smaller yarn diameter, it may take on less water, and thus sag less, because less water weight would be weighing it down. It may be that the two factors are parametric in some way – maybe the lower denier fabric would naturally stretch more than higher denier fabric, and so less weight would be required to stretch it an equal amount. I don’t really know, and don’t have way or time to test it at this point. It was just a thought.
I have 8 LY of Membrane silpoly here at the house and I intend to use it for an X-Mid 2P/Stratospire style canopy when I get around to it. I only want to try the MTN silnylon for a tiny tarp to go with my little mesh tent I made a while back, as I didn’t really care for the 9×9 tarp I had for it(was too big, caught a lot of wind).
Michael,
Sorry, my mistake. For some reason I was thinking of the heavier silnylon from RBTR.
Was also corrected a while back with the knowledge that the .77 OSY has a mini-grid woven into it, which should add to the strength of the material.
If you want to test your thinking, you can pick up around 11″ dia. plastic embroidery loops at a sewing shop or maybe even W-mart. Install and tighten the low denier material in the loop until it is taut. It won’t be tight, because it is so thin, but you should be able to get it taut. Then do the same in another loop with the heavier silnylon of your choice. You might even do a third loop with silpoly if you have a swatch lying around.
Keep the loops indoors and dry for a cold day, preferably with moist weather, and then put the loops outside. Pretty soon you can compare the loops to see how wrinkled they are, and how much the fabric at the centers of the loops can be poked out of shape without any resistance. Just like a wet silnylon tent, the fabric in the loops should become taut again after being brought back into the dry indoors. Might try it myself. Who knows, maybe it is a miracle fabric. But if not, think I’ll stick with the lightest silpoly that I think will hold up.
I think your rules of thumb are appropriate – generally I don’t think the weight savings or performance for the new 7D MTN fabric are going to make a huge difference for most application, even if the fabric is indeed magical as you joke may be the case.
I have samples of the MTN fabric, and compared with the Membrane silpoly, it will definitely be more packable, so maybe in a larger canopy design which is able to mitigate the expansion/sagging issues of the silnylon (assuming it is the same as other silnylon), the pack volume and weight savings will be worth the cost for some. For me, I’m going to use it for a small pocket tarp, so the time/$$$ risk is low. I think both fabrics will find their place in a MYOGer’s quiver.
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