Temperatures at higher elevations

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Hobbes
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Re: Temperatures at higher elevations

Post by Hobbes »

I don't know if any of you guys/gals are into utilizing CLO values, but I've found they're pretty useful for determining basic layering strategies - especially if you're playing around with UL limits.

For those who are unfamiliar with the process, there are models (developed by the military - 'natch) that project metabolic rates for different activities, ranging from sleeping, camp chores/light activities (eg fishing), to strenuous hiking.

Secondly, there are different CLO (thermal) values for various materials, including down, insulation, fiber, materials, etc. (The more reputable bag mfgs calculate their EN 13537 ratings based on CLO values, rather than just throwing some numbers out.) Again, almost all syn materials were developed for military use seeking max warmth/min weight + adverse conditions (read: wet).

So, simply by finding your own baseline comfort range, you can then add up the necessary layers required to keep you warm for different situations. Here's a quick example:

1. At what temperature are you comfortable if sleeping nude? 80, 75, 70? Note that this is the temperature where you would never be chilled or reach for a blanket - for the entire night.
2. Next, add in shorts/t-shirt for a CLO of .4; after than polypropylene LJs for .7. At this point, you've got a CLO of 1.1, which for many people will get them comfortably down to 65. (Again, no reaching for a blanket!)
3. Now we get to the bag. Based on EN, 1.2" of loft (for APEX) achieves a CLO of 4.1 or around 48-52 degrees. (This also coincidentally agrees with Jardine's (100-(40*L)) calculation.) If you add your 1.1 of clothing to the 4.1, you then get 5.2, which is good for around 40 degrees.
4. To get to freezing, you need to come up with another CLO of around 1.0. A down vest is good for 1.3, so that actually gets you to 30. Or, you could go with more insulation and forget the vest. By adding another .6" of loft, that buys you 6.1, or 32 degrees.
5. Add back the vest, and you should be able to get down to around 20-22 degrees without flirting with danger.

Note: all these calcs assume min wind and/or you're using either a bivy and/or tarp.

From a UL perspective, a synthetic (APEX) 30-32 degree/quilt with 1.8" loft weighs around 32 oz (2lbs). Since the LJs come in handy for base layering anyway, they are in essence 'free' add'l insulation. A 12 oz down vest comes in handy if you're hanging around + provides great insurance if temps drop below zero.

Add a tarp/bivy weight of 1lb (including guys/stakes) and a pad/ground cover of another 1lb, and you can see you have 4 lbs for 3 of the big 4. At this rate, a pack can come in under 1lb, so your big 4 comes in under 5 lbs. If you've got 4 lbs of clothing (including rain gear, hoody, gloves, etc) and 1 lb of the 10 essentials, you're now a UL BPer @ 10 lbs base weight. Voila.

Actually, my base is 9, so by adding in bear can+food/water/fuel+accessories, my std 20 degree min, 4-5 day pack is around 17-18lbs. Under 20lb, and a lot of BPers could carry this weight on their shoulders alone. If you add a sternum strap + waist belt + proper compression/load balancing, it feels like you've got nothing on at all.

That's how you can walk miles with your *head up*, looking around and enjoying the day.
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rlown
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Re: Temperatures at higher elevations

Post by rlown »

technically complete, Hobbes.. but.. it's easier to assume that a 15 degree bag is "good enough" for the Sierra (with or w/o a tent depending on pending conditions), and be done with it. For daytime stuff out of the bag, It really depends on the individual to pick his/her gear, if fishing, reading, cooking gourmet meals, or doing camera stuff. It's the "extras" that add the weight. I love the extras.. :)
quentinc
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Re: Temperatures at higher elevations

Post by quentinc »

Hobbes, I think I'd overheat just trying to do that computation. :)

At this point, I just have a 15 degree bag -- it's a Marmot Helium and it's so light I can't see any possible need to get a 30 or 45 degree bag too just to save a few ounces. That said, for September and October backpacks, I find I sometimes need to put on many layers even in the 15 degree bag. I also go through warm and cool spells when I sleep -- sometimes wake up and I'm too cold, put on something and later wake up and I'm too warm. And then the whole cycle repeats...
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Hobbes
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Re: Temperatures at higher elevations

Post by Hobbes »

quentinc wrote:I have a 15 degree bag -- it's a Marmot Helium
Getting a bag, down or otherwise, from a reputable mfg like Marmot (they use EN) solves a lot of problems. The only issues I have relate to the classic down v syn trade-offs.

I fall in the paranoid category, so like Jardine, my brother, and others, we all swear off down in the Sierra. I've had experience with hypothermia from surfing, and one semi-close call @ 11k, my brother had a very close call once in the winter (coincidentally, along Donner - imagine that :eek: ), and of course Jardine has his own two famous episodes which he relates in his book.

I mean, just for example, the stream crossings this year have been treacherous. One slip, and I don't care how carefully you've sealed your bag, and you might be SOL. As some here might have noticed, I almost always go solo, I tend to avoid popular trails, and I fish - all these add up to perhaps a higher risk.

The other issue, of course, is dew/condensation/rain, which practically dictates that you need to carry a 2-ply tent if going in with a down bag, rather than something UL like a silnylon tarp. So, at the end of the day, a 1lb down bag needs a 2lb tent, whereas a 2lb syn bag can get away with a 1lb tarp. Same difference.

Now, if you decide to go with syn, there's a whole world of trade-offs, because the stuff tends to degrade (ie lose its thermal efficiency) much quicker than down. And, of course, it's bulkier and doesn't possess the same thermal qualities (even the newest APEX is a poor comparison to 850 FP), so you're dealing with a heavier, bulkier bag than necessary if it isn't appropriate for the particular conditions.

Since I'm a bean-counter by trade, it was easy for me to pull together the basic research in order to design equip for my own needs, rather than rely on a commercial provider. I know where I go, how I go, and what I do when I get there - I want to minimize risk, but also minimize weight. Ergo, the detailed analysis.
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markskor
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Re: Temperatures at higher elevations

Post by markskor »

Hobbes writes: "The other issue, of course, is dew/condensation/rain, which practically dictates that you need to carry a 2-ply tent if going in with a down bag, rather than something UL like a silnylon tarp."

What?

Maybe just confused (again...so what else is new?)...
Carry a WM Badger (down) and a TT Rainbow -(1-ply silnylon), prefer going solo and often off trail, usually Sierra, high and deep - always fishing. Been doing this for 30+ years with 40 - 50+ bag-nights a year, (often more too)...
and the only thing "dictated" is that I am getting older...Death and taxes.

Guess, according to you and Ray Jardine, must have been lucky all this time?
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oldranger
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Re: Temperatures at higher elevations

Post by oldranger »

Hobbes,

Like Markskor I to travel mostly solo, mostly off trail and use down bag (WM Alpinlite, I'm not as big as Mark) and singlewall Contrail. Have experienced multiple consecutive days of rain/snow and bag has stayed dried. Did get caught in nasty rainy cycle in the 80s with fiberfill bag and first generation gortex bivy. Foot of bag got pretty wet. Contrail properly set up doesn't have the same issues. As a solo hiker the safety margin is really staying within your abilities, making sound judgement concerning terrain, fords, tree crossing etc. and not taking a bite of something you cannot chew. As I get older I find myself taking smaller bites but that is better than not going or getting into trouble. I take the same clothing allotment for all trips except that late August and September I bring extra pair of light long underwear, a 100 weight fleece top, and a heavier fleece cap in addition to my standard gear. The extra long underwear and fleece top, and cap are primarily for sleeping comfort as I use my wool sweater and down vest as pillow stuffing and to wear them when I sleep would seriously impact my comfort.

Mike
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Who can't do everything he used to and what he can do takes a hell of a lot longer!
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Hobbes
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Re: Temperatures at higher elevations

Post by Hobbes »

markskor wrote:Guess, according to you and Ray Jardine, must have been lucky all this time?
Trust me, no one picks syn over down because they actually prefer it. I mean, let's be truthful, there's simply no comparison. Who wants to carry something twice as heavy + twice as bulky that achieves the same thermal result?

If I had your confidence, I would have a down bag. I don't, so I don't. And please don't infer that I'm implying that you're 'over' confident. I admit I'm a wimp; a man has to know his limits, and the way mine are, I'm going with an insurance policy.
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