Re: Temperatures at higher elevations
Posted: Fri Aug 12, 2011 12:41 pm
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.
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.