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Bivy sack as rain shelter

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Bivy sack as rain shelter

Postby JHH60 » Tue Oct 12, 2010 12:37 am

How practical is a minimalist bivy sack as a rain shelter on planned overnight trips, especially without a tarp? It would be great to have something for solo trips that weighed less than a tent, could be thrown on top of a pad without a lot of fuss or setup time, allowed one to sleep under the stars if the weather were fair, but could be zipped up to quickly provide some shelter if it started to rain or snow. I'm not necessarily thinking about mid-climb bivy scenarios where a bivy sack is the only choice because a tent won't fit on a ledge, but rather as a fast and light alternative to a tent for approaches or even solo backcountry camping.

I was specifically eyeing a Marmot Alpinist sack that REI has on sale now. It's pretty simple (basically a bag with a "breathable" top layer and a zipper entry), light and cheap, which are all nice traits. But I was trying to figure out whether, if it really started to rain, I could keep reasonably dry inside without some kind of protection above the opening over my face (or nose, at least) that I'd need to breathe. I could certainly bring a tarp in addition to the sack, which then (+ bivy sack) starts to approach a tent in terms of weight and setup time. I have known people who had fancy bivy sacks with poles that kept the fabric of their faces and created little mini tents over their heads, but those are also starting to approach tents in their setup time and complexity. And tarps and mini-tent bivy sacks both dimish the sleeping under the stars experience a bit.
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Re: Bivy sack as rain shelter

Postby adventurer » Tue Oct 12, 2010 1:46 am

A few years ago, I bought a product then made by Integral Designs called the "Endurance Bivy". From your description of the Marmot Alpinist sack, they sound very similar. The Endurance Bivy is nothing more than a long sack made of waterproof and breathable event material. It has a hood and a velcro closure at the head.

I've used it a number of times with a pad to sleep out under the stars. I just stuff my sleeping bag inside and I'm all set.

On a few occasions there has been rain or sleet while I was using it. I'd say that I managed to stay 98% dry under those conditions. If it rains hard enough, there is always some leakage in near my head but nothing that really bothered me.

All that said, I'm always pretty conscious of expected weather conditions and/or the length of my trip. If the weather looks like it might go to heck before I leave, I take my EV2 tent and live with the extra 5lbs. Same if the trip is too long to reasonably rely on prior weather forecasts.

I tend to think of my bivy sack as a fair weather shelter for planned usage or an emergency shelter if needed.
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Re: Bivy sack as rain shelter

Postby Sierra Ledge Rat » Tue Oct 12, 2010 3:47 am

I was once under the delusion that a bivi sack was a great shelter in all kinds of weather.

Funny how that delusion never seemed to change, no matter how many times I went out in the rain and got my sleeping bag soaked in a matter of minutes every single time.

Strange how that delusion didn't even change the time I was up on an alpine big wall and got soaked in my bivi sack and then it all froze to solid ice when the temperature dropped and I barely made it off the wall alive.

Fast forward many years... As a wise old man I now realize that a bivi sack is wonderful for keeping the dew and wind off you when the weather is clear and no rain is forecast. But I will never again use a bivi sack as a primary shelter if there is a chance of rain. Snow, maybe. Rain, no.

Some of my bivi sack experiences:
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Re: Bivy sack as rain shelter

Postby rhyang » Tue Oct 12, 2010 4:50 am

Bivy sacks are basically an exercise in misery. I've used one above treeline in the summer / fall for keeping the weight down as a just-in-case shelter if the forecast is good. But generally I'd rather sleep out, under a tarp or in my Firstlight.

I agree, they can help with wind, and sometimes condensation (though they are notorious for accumulating condensation on the inside in some conditions).
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Re: Bivy sack as rain shelter

Postby dan2see » Tue Oct 12, 2010 4:54 am

Aren't those things supposed to be carried, in case you are forced to spend the night out? So if you plan to stay overnight, you should plan something better?

I have sometimes carried mine just in case I get stuck in some area where might get home by dark, but I absolutely cannot travel at night. The idea was, I don't have to like it, but I will survive. So comfort is not the issue: hypothermia is.

Last summer I did use my bivy for camping, under the stars. The weather forcast was "clear", so I knew I would not get rained on, but I would protect my sleeping bag from the morning dew. It worked. But actually a simple space-blanket works just as well.
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Re: Bivy sack as rain shelter

Postby JJBrunner » Tue Oct 12, 2010 5:58 am

I picked up an Outdoor Research Advanced bivy in the beggining of summer. It has two poles and feels like a cross between a bivy sac and a tent. Weather hasn't allowed me to test it in the rain yet but I have slept in it almost sealed up (it has a few different options using the poles). I imagine if I was in the open with nothing to cover the head area and had to seal the bag up that condensation would be an issue, especially with a down bag. When I slept with the sealed bag, there was a lot of condensation, however, when the head area was open it was not a problem at all. I figure if it's going to poor, I'll just throw something over the head area and leave the bivy open there.
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Re: Bivy sack as rain shelter

Postby JJBrunner » Tue Oct 12, 2010 6:02 am

And I believe it was Craig Connally in "The Mountaineering Handbook" who talks about waiting out a downpour in his bivy bag laying face down with the opening to the ground...
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Re: Bivy sack as rain shelter

Postby mvs » Tue Oct 12, 2010 9:14 am

JJBrunner wrote:I picked up an Outdoor Research Advanced bivy in the beggining of summer. It has two poles and feels like a cross between a bivy sac and a tent. Weather hasn't allowed me to test it in the rain yet but I have slept in it almost sealed up (it has a few different options using the poles). I imagine if I was in the open with nothing to cover the head area and had to seal the bag up that condensation would be an issue, especially with a down bag. When I slept with the sealed bag, there was a lot of condensation, however, when the head area was open it was not a problem at all. I figure if it's going to poor, I'll just throw something over the head area and leave the bivy open there.


I've got that one. I've used it in the rain, sometimes with success, other times being surprised and waking up with a squishy bag. The problem is I never figured out what caused it to fail sometimes and not others.

That makes for a particularly troubled sleep when it's raining! :D
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Re: Bivy sack as rain shelter

Postby mfox79 » Tue Oct 12, 2010 12:30 pm

15 years agoe I purchased one of the first Outdoor Reaserch bivy bags with poles and used it with great success till I experienced a freak snow storm in the Wind River Range that dumped 8" of fresh powder. this should have been a good warning to stop using it but then I was pinned down for four days in the Uintas after that. this was a set up with poles and it was a great few days of misery, I now use an older BD Megamid or 1 person tent as a plan b. if you dont mind the soud of buckets of rain or even a slow water tourture then it may be the perfect choice. just not my thing anymore.
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Re: Bivy sack as rain shelter

Postby goldenhopper » Tue Oct 12, 2010 3:11 pm

As mentioned by many, USELESS! That said add a small sil-nylon tarp and choose the right spot and you're golden for an extra 12 ounces or so.
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Re: Bivy sack as rain shelter

Postby JHH60 » Tue Oct 12, 2010 7:29 pm

Thanks guys. Might have to dust off my tarp rigging skills for the times I don't want to take my tent. I spent a month under one in the Rockies when I was in high school and got quite used to it, though I was using a synthetic bag at the time so it didn't matter if it got a little wet.
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Re: Bivy sack as rain shelter

Postby MoapaPk » Tue Oct 12, 2010 8:28 pm

Do you use trekking poles? There are some tarptent options with trekking poles. A friend weathered a storm on Shepherd Pass with this.

I used a tarp (with mosquito netting sewn around the bottom) for my youth in the NE; but it was dagnably hard to set up on rocky summits.
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Re: Bivy sack as rain shelter

Postby CClaude » Mon Oct 25, 2010 7:29 pm

I've spent 5 days waiting out a snow/rain storm (in a Bibler BigWall Bivisac). It is an exersize in frustration/misery/ clausterphobia but I did stay reasonable dry.
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