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Euler
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Euler
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PostMon Sep 18, 2017 10:00 pm 
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Idea: 6 oz tarp + 3 oz space blanket. Then, in an emergency, just lay under the tarp. Possibly rig to be up a little bit using rope that I currently bring alone, or, replace some of the rope with guy lines. Maybe add stakes. This would still be less weight than the blizzard bag, and seems to be better more effective. Ventilation should be much better than in a bivy. Would continue to bring the pad. Maybe add floor mat. Whaddya think of all this?

Zdarsky tent looks a lot like a bothy bag.

I'm still not clear about conduction from a bivy, with snow or rain on top - the original thing I asked about. A tarp would seem to have the same question, if just right on top of me.
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InFlight
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PostTue Sep 19, 2017 7:35 am 
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A few comments from the resident Mechanical Engineer...

Heat transfer consists of Convection (Air Flow), Conduction (Direct Transfer), and Radiation.

Conduction
Our Clothing Layers and shoes act as insulation to reduce conduction with the ground and air normally.  Obviously when lying down, we need a insulate our self's from the cold ground with a pad.

Convection
Convection is the classic wind chill factor.  Insulation layers that are non-wind permeable tend to address this issue well.  The rain gear we normally carry provides excellent protection.

Radiation

During the day solar radiation normally provides considerable heat.  At night we radiate heat directly to the very cold outer space.  A insulation layer can greatly reduce radiative losses. That's why they put the floating bubble wrap on pools at night.

Rain and sweat can greatly reduce the effective insulation properties of the clothes we are wearing. Staying dry is the key to survival.

If I had to survive a night or two outside, a full rain suit (dry ducks @10 ounces)  and a pad (Thermarest Z @ 10 ounces) would be my two item light weight selections.   You could comfortably sleep beneath a tree for additional rain and radiation protection.

The space blankets and bags help with convection and radiation heat loss.  They would be a nice very light extra, but would be a fourth item selection in not higher.

A tarp set up correctly would keep you dry and help with convection, and radiation.  Some full rain cover and additional wind protection would be my third selection.

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I went to the woods because I wished to live deliberately...  ― Henry David Thoreau
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DIYSteve
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PostTue Sep 19, 2017 9:16 am 
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InFlight wrote:
If I had to survive a night or two outside, a full rain suit (dry ducks @10 ounces) and a pad (Thermarest Z @ 10 ounces) would be my two item light weight selections. You could comfortably sleep beneath a tree for additional rain and radiation protection.

What if you're above tree line? All but one of my emergency bivis have been in places with no trees. A tarp would have greatly helped, either erected (in rain) or used to wrap me up (no rain or rain with strong whipping winds when setting up a tarp would be impracticable). One of the benefits of a tarp is that it can be used in different configurations.

My most comfy e-bivi was a solo affair tucked under a White Bark pine krummholz.
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RandyHiker
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PostTue Sep 19, 2017 10:00 am 
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Euler wrote:
Zdarsky tent looks a lot like a bothy bag.

FWIW:

Zdarsky was an Austrian ski pioneer in the 1920s and 1930s.

Bothy is a UK term for a public mountain hut.  So a Bothy bag is simply a UK centric term for a similar item.

Commercial bothy bags show them used with two inhabitants facing each other and their backs to the outside and leaning against the fabric.

Zdarsky tents are typically used with occupants side by side or spooned to minimize exposure to the cold.  Most people dispense with any inhibitions about cuddling during a cold unplanned night out.
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Riverside Laker
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PostTue Sep 19, 2017 10:30 am 
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InFlight wrote:
Heat transfer consists of Convection (Air Flow), Conduction (Direct Transfer), and Radiation.

And... Phase change like evaporation.

MSME Thermodynamics.
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HitTheTrail
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PostTue Sep 19, 2017 10:35 am 
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DIYSteve wrote:
A tarp would have greatly helped, either erected (in rain) or used to wrap me up (no rain or rain with strong whipping winds when setting up a tarp would be impracticable).

The hammock folks sell a tarp sleeve made out of silpoly that weights 1.5 oz. Like DIYBS says, you roll your tarp up like a burrito and slide the sleeve over it. To deploy the tarp just attach the tarp lines to a couple of trees and start sliding the sleeve off, staking out your guy lines to the ground as you go. These same people sell a cuben tarp with doors that is less than 10 oz and completely waterproof. Cuben will not wet or absorb water.

I use these all the time with my hammocks. Even in high winds tarps are easy to set-up and take down.
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InFlight
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PostTue Sep 19, 2017 2:42 pm 
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Riverside Laker wrote:
InFlight wrote:
Heat transfer consists of Convection (Air Flow), Conduction (Direct Transfer), and Radiation.

And... Phase change like evaporation.

MSME Thermodynamics.

Phases changes are a thermodynamic effect due to heat addition ( melting, vaporization ) or heat removal ( condensation, freezing) that doesn't change the chemical composition.

The methods of adding or removing heat are strictly Heat Transfer consisting only of Convection, Conduction, and Radiation.

Clearly the minimum gear selections in more severe environments above the tree lines or in winter mountaineering are quite different.  This started as a day hiking gear discussion.  The most important survival equipment is between your ears.  There are a lot of natural materials that you could make a shelter out of in need.

Packing some type of rain gear in the PNW is a requirement, getting completely soaked without rain gear is the one thing that would really put you in a bad survival situation.

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I went to the woods because I wished to live deliberately...  ― Henry David Thoreau
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Bernardo
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PostTue Sep 19, 2017 4:27 pm 
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The OP was talking about a night on the Muir snow field.

I'd rather have a tarp than rain pants.  With a tarp you can create a dry space.

The OP set the condition of no poles.  Unless you are rock climbing, I see poles as an essential survival item.

In the woods, your chances of getting a fire going are a lot higher with a tarp.
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DIYSteve
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PostTue Sep 19, 2017 4:50 pm 
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OP didn't mention Muir Snowfield in his original post, which was vague re location or terrain.

For sure, I'd rather have a tarp than rain pants for a e-bivi.

Hiking poles as an "essential survival item?" I'll try to wrap my mind around that.
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Bernardo
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PostTue Sep 19, 2017 6:05 pm 
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Well, maybe essential item is overstating but Euler said he doesn't carry poles  and this was one reason against tarps. 

But if you are talking about items beyond the 10 essentials, I think poles are pretty high on the list.  They help you avoid falls and could extend your range if you are tired or hurt thus possibly obviating the bivy.  Although not essential, poles make using a tarp much easier.  So if your trying to ratchet up your safety and dryness level, I think poles make sense.   So nice to have more than essential.
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InFlight
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PostTue Sep 19, 2017 6:25 pm 
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Bernardo wrote:
Well, maybe essential item is overstating but Euler said he doesn't carry poles  and this was one reason against tarps. 

But if you are talking about items beyond the 10 essentials, I think poles are pretty high on the list.  They help you avoid falls and could extend your range if you are tired or hurt thus possibly obviating the bivy.  Although not essential, poles make using a tarp much easier.  So if your trying to ratchet up your safety and dryness level, I think poles make sense.   So nice to have more than essential.

I day hike with trekking poles and a camera tripod.  I could probably come up with some really creative tarp pitches!

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I went to the woods because I wished to live deliberately...  ― Henry David Thoreau
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RandyHiker
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PostTue Sep 19, 2017 6:59 pm 
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SilNon Tarp + a bit of parachute cord + experience making burritos = something resembling a bivi bag.

Yeah it will get a bit clammy compared to a fancy goretex bivi bag.  It will keep the cold rain off your insulating layers and reduce wind chill heat loss.

Below timberline, parachute cord + pine cone or a small rock or whatever = a tie out to hold the tarp up off your body and reduce clammy effects.   You can also use a stick as a tent pole (and pegs) instead of carried gear.  A knife is super useful in this regard -- one of the reasons its one of the "ten"
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Euler
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PostTue Sep 19, 2017 9:58 pm 
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I don't have a clear answer about conduction but there have been some interesting thoughts here. Thanks.  Hmm, tarp sleeve, hadn't seen that before.

Someone mentioned day hike, and someone seemed to have lack of clarity with scenarios. Day hike: I'll say that a day hike could mean I'm more than 10 miles and thousands of vertical feet from the trailhead. I rarely if ever intentionally go above class 2 scrambling, but I have done at least class 3 intentionally and unintentionally. Some of the day hikes are snowshoeing hikes. So yes, along with the day hike label comes some truth that there are some places in Washington state that I will not be, but there are many, many places that I could be, in many different situations. Most of the time I'm below tree line, and a typical day is hiking to Surprise Lake and Trap Pass. But most only means > 50% and there is a lot of variability in the kinds of things I do. Often I'm above treeline for extended periods of time. Examples include Camp Muir, Mt. St. Helens summit, Mt. Adams summit, Mt. Elbert summit, Big Craggy summit, near Cloudy Peak summit. I go backpacking about once a year. Scenarios: for additional clarity about the two scenarios I'm most concerned about, see the second paragraph of my post from Sun Sep 17, 2017, 11:15 am. I hope this clears up any confusion about what I am planning for. I'm happy to listen if someone thinks there are other ways of thinking or other scenarios I should be thinking about.

There was discussion about poles. Sometimes I take super-light carbon fiber poles, but I usually don't take poles because they hurt my wrists, I'm not sure that in the long run my balance is better with them (I learn by not having them), and they are added weight. I could be convinced to take one or more poles as a matter of course, though.

Someone mentioned a knife and, I think, paracord. I do carry a knife and some rope. If I start taking a tarp I'll probably replace some of the rope with guy lines.

I'm wondering if anything will stay dry in a night of 35 and rain, even if I'm under a tarp - humidity would be high. Maybe it's time to once again think about vapor barrier techniques.

I'm reminded that circa 10 years ago, The Mountaineers recommended a tarp for winter travel. After haering that,I got one from REI with a reflective coating, 8-16 oz total weight I'd guess. Silver coating on one side, red on the other. I saw this tarp other day at the REI web site, but don't see it now. I carried it in my pack for a year or two. Then, I ditched it to make my pack lighter and I didn't have good knowledge about how to use it.
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RandyHiker
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PostWed Sep 20, 2017 12:08 am 
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Euler wrote:
The Mountaineers recommended a tarp for winter travel.

FWIW: In the mounties ski trip leader training I took they covered building a quick shelter with a tarp. 

Basically this consisted of stomping a pit in the snow, sticking ski poles and skis into the snow at the edges of the pit to make a four poled tipi and wrapping the tarp around the skis and poles and crouching down inside on top of your pack.

This type of shelter has the advantage of being very quick to construct, not requiring any tools and building it doesn't involve much contact with snow.

More elaborate snow shelters -- such as a snow trench with snow blocks in an A frame roof over the trench -- require more time, a snow shovel and snow saw and involve considerable handling of snow -- which can result in damp clothing.

Another aspect favoring quick and easy construction is that the same circumstances that are forcing the unplanned night out are likely to make building a better shelter difficult.
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Euler
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PostWed Sep 20, 2017 12:40 am 
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Hadn't heard of that method. Good to know! Even with two poles it might be possible to get something pretty decent out of that. Agreed about the circumstances making building a better shelter difficult. That is one reason I was thinking about the bivy. With the pit-stomping method, if you are in bad shape, you could make the pit, rest and warm up some, and then build something better if you feel better.

In one Mountaineers class, we selected into little groups and then spent about 20 minutes building a shelter. We found a nice space between some trees, didn't really get the tarp up, but had something or other we could get in.
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