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Seeker
2006-01-29, 01:47
please bear with me... it's a long post...

I have my HH Backpacker Ultralight Asym set up in my backyard a lot of weekends, and sometimes during the week, waiting for it to rain (i know, it's a little odd, but aren't we all?) i can try out different tarp configurations (stock and 8 x 10) that way. lately i have also been experimenting with my christmas present, a JRB underquilt, but that's a whole different test.

today, out of nowhere, we get a torrential downpour that goes on for about 2 hours... like the proverbial cow on a flat rock... all straight down, no wind blowing it sideways... nice 70* summer day in january... (another "wtf?" moment). my hammock's out there with the underquilt and weathershield, and the stock tarp. so far, so good...

i went outside planning to climb into the hammock and watch what rain comes in from where, as i've done many times before, when i realized the rain was actually spraying THROUGH the silnylon stock tarp, like it was a window screen or something... not big drops, more of a heavy misting. and no, it wasn't foggy. and this isn't one of my homemade deals. it's the tarp that came with the hammock. i'm standing there underneath, getting rained on and wondering 'where the h#// did THIS come from?' in a recent discussion (here or on WhiteBlaze) about whether silnylon leaks under pressure, i took the position that it doesn't... there were some points made about water bags as well, and you can't make a water bag out of something that leaks, right? so now i've experienced it myself, first hand... lanthar, if my aged memory serves me right, you were the one who did an experiment with a tarp full of water, proving that it doesn't, and cant', leak, even with a heavy load of water...

has this ever happened to anyone else? i've been out in the rain in this same tarp/hammock combo before, but it's never leaked/sprayed like that. so the question is this.... will this always happen, given a hard enough rain, or does silnylon get to a point, wear-wise, where you have to re-coat it to prevent it from driving right through the fabric? or is it some sort of al-qaeda/communist/liberal plot to make me think i'm nuts?

dropkick
2006-01-29, 06:23
has this ever happened to anyone else? i've been out in the rain in this same tarp/hammock combo before, but it's never leaked/sprayed like that. so the question is this.... will this always happen, given a hard enough rain, or does silnylon get to a point, wear-wise, where you have to re-coat it to prevent it from driving right through the fabric? or is it some sort of al-qaeda/communist/liberal plot to make me think i'm nuts?

I don't have a lot of experience with silnylon yet, but when the same thing happened with canvas it's time to retreat the material.
I've had the treatment on canvas give out suddenly before too. Good one day and leaking like a sieve the next. (why I started treating my canvas tents yearly).

P.S. I'm pretty sure there isn't any plot against you, but I'm having Capt. Bob (the invisable chinchila who lives in my hair) check on it, just to make sure.

Rosaleen
2006-01-29, 09:38
Seeker-

The only time I've seen anything close to this was when raindrops knocked condensation loose. You could do a quick experiment, gathering your hammock fly into a makeshift pouch and trying to fill it with water. If you find any water oozing through, try spraying your fly with as close to 100% silicone as you can find. Kiwi and Atsko make some. Try shoes or sporting goods sections of WalMart if that is convenient.

Cheers!

Rosaleen

Just Jeff
2006-01-29, 12:18
Filling it with water won't subject it to the same pressure as a heavy rain. Furthermore, the water's force will be spread across the fabric's surface rather than concentrated at one point, as with a raindrop (or actually many points in a storm, but still not uniformly distributed).

There seem to be two camps regarding sil's waterproofness. Those who claim it's waterproof and those who've experienced otherwise. If the principle of it only being waterproof to a certain pressure is true, then it'll happen in any storm like that. If it's not true...then you've just experienced the same impossibility as everyone else saying sil isn't 100% waterproof in heavy storms.

In a rainstorm, I've only experienced the rain knocking condensation onto me. In that Sierra blizzard, though, I'm pretty sure the wind was blowing the snow through the Golite Hex's material. We shouldn't have been producing that much condensation, consistently and over time, when those winds were providing us with some pretty good ventilation inside the tent. But this wasn't a controlled test...

Seeker
2006-01-30, 15:52
hey guys... thanks for the thoughts... after a long conversation with peter pan this morning, i think it was an issue of condensation being knocked loose... the weather conditions (sudden rain-drop in temp-humidity) seemed to favor that answer anyway... but i retreated the tarp just to make sure. thanks again for your input.

Salvelinus
2006-01-30, 18:17
Wait a minute, Seeker. Why would you have condensation UNDER your tarp before you were actually under it? Maybe I'm missing something obvious here, which is likely considering the day I had at work. I understand dew and how it forms, but doesn't it usually form on TOP?

The reason I'm interested is because I am in the planning stages of sewing a silnylon tarp. I've heard of this problem before, and if the material doesn't do what it's supposed to, I'll modify the plans (and material).

Seeker
2006-01-30, 19:02
as i understand it, the air was really humid. a cold front carrying rain moved in, suddenly cooling one side of my tarp (the top, pitched into the wind), causing all that humid air underneath to condense... not sure it's so much a defect or caused by silnylon as it is just a natural occurance... i've seen dew condense inside a shelter's tin roof too.... the rain didn't knock it off though, because the metal is too thick to move when the rain hits it... a tarp though, being thin, moves when the rain hits it, causing a slight 'spraying effect'...

sounds like a real scientific answer there, doesn't it?

coincidentally, there was a post about this same subject over on whiteblaze today... Sly answered it pretty well... hope this all helps...

Salvelinus
2006-01-30, 22:07
Thanks. That must have been a very rapid temperature change. We've had a few of those here the last couple of weeks, too.

I've had the (dis)pleasure of waking up to a fine mist in my tent before--which, after imagining a huge hole in the tent and then fully waking up, I eventually realized was condensation being knocked off. I just never dreamed it would happen under a tarp.

I'll check out whiteblaze. Thanks!

Just Jeff
2006-01-30, 22:22
Why would you have condensation UNDER your tarp before you were actually under it?

Happens all the time here in Monterey. As long as the wind isn't shaking it off, I just carefully get in the hammock and the ventilation dries it before morning.

It only happens when I set up the tarp just before dewpoint hits, then go off and fiddle without getting inside. When I hike, I usually set it up and get right in...I think that would help. Counterintuitive, huh?

Like Youngblood says...no system will work well in 100% of the conditions you'll encounter.

PKH
2006-01-31, 07:08
Seeker, I have experienced this misting effect a few times - always in a hard, driving, prolonged rain. This is not to be confused with the odd bit of condensation splatter, which I actually find more unpleasant, as the water droplets are larger and nastier. I note that Henry Shires, a fellow who I am sure thoroughly understands silnylon fabric, warns of this in the FAQ section of his Tarptent website. For me it has never been a problem. The occasional light misting has never been enough to get me wet (it has worried me of course!), and it has only occured during truly torrential downpours of almost biblical proportions.

Cheers,

PKH

Seeker
2006-01-31, 11:39
thanks... like i said, it was torrential, and i've been here almost 4 years and hadn't experienced any problems til this weekend...

thanks again to all for their input...

Salvelinus
2006-01-31, 22:10
Thanks, guys. I guess I'll proceed with the silnylon. Really didn't want to give up the weight savings over PU coated, anyway. :D I'll post specific questions about the tarp in another thread.