Mar 4, 2009 at 4:36 pm #1234533
So I think I want to make a half bag/elephant's foot. Before I get materials and put real designs on paper, I have a few questions.
The inspiration for the project is the MLD 2Thirds Quilt and the Nunatak Arc AT. The quilt will be used with a Montbell UL Down parka or a UL Thermawrap – other torso clothes include Patagonia 1 LS and GoLite Ether.
My idea is to have the whole thing look like a cone that has the tip cut off. Like the MLD quilts, the footbox would be able to open and close with a draw cord. I could also sew the footbox flat, maybe. The insulation will be ThruHiker 800 down and with 0.75 inch baffles; baffle height is taken from Nunatak's Arc AT and is otherwise arbitrary. I would like the quilt to be good to approximately 35-40 degrees.
Construction would be to make the quilt flat, then sew the side edges of the quilt together to make the cone.
The first question pertains to the height. How far up my body should it go? The MLD Spirit Short (formerly 2Thirds) is 54" long and has a draw cord closure on the footbox. My gut tells me that it should go only my true waist, so that when the draw cord is tightened it cannot slid off me because of my hips. Accounting for a draw-cord footbox (5" radius when closed; my feet are 10" long), that is a 48" quilt height.
About that footbox. I have used a sewn-flat footbox (a la Jardine and the Bill's recent XP/Cuben quilt) and do not like it. I can sew in a footbox, 12" in diameter with one baffle, but is it worth it? I like the idea of venting. Will it be drafty if I do not sew it up or make a closure flap?
Second, what about going with a top-bag style and leaving no insulation in certain areas, such as underneath my butt and running down until the bag would start to fold over my foot. In otherwords, only the bottom three baffles would go all the way around; the rest there would only be a 10-12 strip of single-layer Momentum underneath me. Any thoughts? I am leaning away from this option.
Third, what about top and bottom widths? I want the bag to fit snuggly for maximum thermal efficiency. How many inches above my butt girth should it be? I am thinking approximately 3-6 inches. What about that bottom width? This is complicated some because if it is not wide enough, my feet will pull more fabric from the sides. The MLD quilt has a 32" bottom. Any thoughts?
Finally, how much down should I shove in there? With a 48 x 43 x 32 (Height x top x bottom) dimensions, that is 1800 square inches of insulation I need to fill. Filling to 3/4 inch would mean I would only need 1350 cubic inches of down, or 1.6875 ounces. That does not seem right – Nunatak uses 3.5 ounces in even their smallest Arc AT. Thru-Hiker only sells down in packs of 3 oz. In an e-mail conversation with Tom at Nunatak, he said a 1 oz overfill would be fine on an Arc AT, bringing the total fill weight to 5 oz and thus 4000 cubic inches of down. If I did that, I would be stuffing my baffles to approximately 2 inch height!
What to do?
Total weight? Sub 8 oz is the goal. My calculations show that the shell and lining will weigh 1.29 ounces each; that leaves 5.42 ounces for down, baffles, draw cords, cord locks and thread. Cost is about $122.14 from thru-hiker, assuming I buy 6 oz of down – about $121 cheaper than from Nunatak (assuming I do not go with 0.8 Quantum and get 1 oz overfill).
Thanks.Apr 5, 2009 at 8:20 pm #1491548
I made a prototype of this tonight out of a two person top bag I sacrificed to the MYOG gods. Material was Momentum on both sides with 5 oz XP; weight is 313 grams/11.04 ounces. It is a little short, but should be long enough to cover the jacket gap. I am planning on making this in a down version and adding 4 inches to the length/height.
Pics later Monday night.
This thing is heading out for its first use this coming weekend. Sleeping in a double bivy with Jacci (although she thinks I am crazy) under a tarp. Temps and location unknown right now, but it will be within about 1 hour of the St. Paul/Mpls metro area.Apr 5, 2009 at 8:32 pm #1491554
Devin MontgomeryBPL Member
@dsmontgomeryLocale: one snowball away from big trouble
Excellent, look forward to them!Apr 5, 2009 at 8:35 pm #1491556
Jason BrinkmanBPL Member
I don't have any advice for you, but I am definitely watching for the outcome. Keep us posted.Apr 6, 2009 at 9:15 pm #1491912
External dimensions are 46 height; 34" bottom circumference; 44" top circumference. It goes up to my naval and overlaps with my MB inner down parka by about 2", which should be sufficient for coverage purposes. I'll test it this weekend and check it; if it works fine, I will not add height to it. I will be in a double bivy under a tarp. Expected temps and location are currently unknown.
FYI – pad is 31" x 21" – enough to lay my hands at my side.
Apr 7, 2009 at 4:09 am #1491945
@ramblerLocale: On the AT in VA
Nice thoughtful job. With a double bivy you should be fine. But, if you had a full length bag, could you leave the bivy at home? I have not used a bivy in summer under a tarp and a full quilt. That said, I would try your system. You can always add-on or stuff in more down if needed.Apr 7, 2009 at 5:43 am #1491954
Matt, great job. Jacket and half-bag are awesome systems. Let us know how it works our for you.Apr 13, 2009 at 11:21 am #1493651
I took this out this weekend for the first test, with mixed result. Something in my system failed, but I'm not sure what. I do not think it was the bag.
Temps were above freezing (but definitely in the 30s), and I was wearing capilene 1 tops and bottoms, a windshirt, MB UL down parka, powerstretch gloves, fleece beanie and dry socks. I was sleeping on a torso pad with my feet on my pack and poncho/tarp (cushy!). I ate a warm supper late into the evening and had some chocolate before bed. For shelter, I was under a tarp and in a Dixon Double bivy with Jacci.
I was slightly chilled over all with no significant individual spots of coldness. I was especially watching for coldness in my legs, which did not happen. My toes did get cold, but I slipped on my extra pair of socks on my feet like half socks (only to arch). This points to me as either a failure of a few things: 1) torso pad (old blue foamer) is collapsed and needs to be replaced; 2) mild dehydration, as I had about 16 oz of water from 7 p.m. on, plus mildly soupy pasta.; 3) Montbell Inner Down Parka was not good to those temps.
My best guess is the mild dehydration, next the parka and then the torso pad. Everytime I got up and pee'd, I was warmer when I got back (of course), but drank some water, too. I should have used my R1 hoody instead of the Capilene 1 LS top, too. The down parka didn't have any cold spots, it just didn't feel like I was warm enough. It was an odd feeling that I have not experienced before.
Anywho, dimensions were fine. The bag covered the gap nicely, and it compressed well enough in my pack (Z1 from Zpacks) to be used without a stuff sack (first time used technique and LOVED it). My feet did not notice any drafts in the bottom and the top drawcord effectively sealed off top.
I did not sew the insulation into the fabric on the top and bottom of the quilt, and it slip down throughout the night. If I make another synthetic quilt, I will definitely sew it in.
I think this is good enough to make a down version of it. More later.
Thanks for comments and reading.Apr 13, 2009 at 12:55 pm #1493669
Jim ColtenBPL Member
Everytime I got up and pee'd would seem to argue against very much dehydration. It'll take more nights at about the same temp to test that. I'd be inclined to look towards insufficient insulation.
The 5oz XP in your half-bag is probably about right for mid 30's (F) … at least it would be for me.
Not being familiar with your parka, I can't say much about that.
The pad … what's needed is largely a function of the ground (or snow) temperature.
But regarding your intent to move to down … in other parts of this thread I detect a hint of "an inch of down is equivalent to an inch of synthetic" thinking. I don't believe that is true. Choose your down thickness based on Clo. Clo/oz/yd**2 values are easy to find for XP and PL Sport and PL1. Not so available for down. But I recall Richard Nisley offering some info along those lines in another thread … if only I could find it.Apr 13, 2009 at 1:29 pm #1493684
Jim: My comments about dehydration stem from two things: 1) I normally drink a copious amount of water; and 2) my urine output each time I got up was definitely less than normal.
As for the down, I am familiar with Richard's posts re: down density and CLO for 800+ down. I have not run the numbers on my quilt to check down densities, but I plan on packing it reasonably tight to take advantage of the increased efficiency of down as its density increases. When I figure out how I am going to put this all together, I'll post numbers and calculations as to how it will all work.
As for the pad, I did not feel cold coming up from underneath me, as I have in the past (torso pad + 3/4 Ridgerest + Vapor Trail under feet is not sufficient for me at -7 F, for example).
Best Clothing Combinations: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=9378
Paradigm for understanding warmth: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=18950
More links later as I find them.
What I have not figured out is to how to calculate these values, especially as down density increases.Apr 13, 2009 at 1:43 pm #1493687
Staying warmm, or should I say understanding why or how to stay warm, becomes more complicated as you push the limits of your sleep system. Sometimes little things like not drinking enough or eating too early in the evening can effect my comfort level. If I know the night is going to be a cold one, I start to cram food and water down my throat – it "usually" does the trick.
Assuming Jacci is your girlfriend, how does she like your half bag system? My girlfriend hates my half bag combo and thinks my z-packs blast looks like a garbage bag.
I was just re-reading your post. It's been a while since I had my MB Down Inner, but if it dropped to freezing or very close to it, that may be pushing that parka just a bit. Standing around camp is probably fine, but sleeping all night may become a problem…just guessing here. I think I took mine to 40* or so (can't remember off hand) and was fine but I find the next 5-10 degrees a tough drop to swallow. Keep on testing my friend!Apr 13, 2009 at 1:45 pm #1493688
Nia SchmaldBPL Member
I don't have the calculations for the montbell UL parka but my guess is that is the problem. An 8oz sewn through down jacket with half of it compressed by body weight seams pretty minimal for temps in the 30s. My guess is your entire torso was cold which is why you couldn't pinpoint a specific source.
Nunatak rates their half quilt + skaha down to 40. And the skaha I'm sure is significantly warmer then the montbell UL.
I'll be interested to see the calculations.Apr 13, 2009 at 1:53 pm #1493691
I'll just add that the Skaha is a major upgrade from the MB Down Inner…but that's why you pay through the nose for it. I have an ounce of overfill in mine so it is warmer then the standard but I couldn't wear mine if it is above ~40* or so…you'll melt in your bivy.
Good thing about the MB is that you can use it when the temps are a bit higher. My guess is you will be much more comfy when it is 40/45 out…probably a perfect system for that range.Apr 13, 2009 at 2:05 pm #1493694
Jacci is my girlfriend – the Minneapolis folks will meet here (finally) on Saturday.
Jacci thinks I'm crazy, and this single quote states her general opinion on my hobbies: "I fail to see why you continuously push normal activities to dangerous extremes." (re: my aborted SHT winter trip, ultrarunning, fastpacking, etc.)
But she understands me and wouldn't change me for the world. She also understands lightweight hiking. She requires some level of comfort (hooded sleeping bag, self-inflating pad (Thermarest), and others).
@ Steve: I know I am susceptible to minor changes in my food and liquid intake, and running and hiking more has shown me how to more effectively monitor and manage that.Apr 13, 2009 at 2:19 pm #1493698
Jacci thinks I'm crazy
I fail to see why you continuously push normal activities to dangerous extremes
hehehe…I think we're dating the same girl. :)
On a serious note, I'm learning alot these days aswell. I never really took into consideration (or monitored) my food and water intake until recently. I just used to eat whatever I had when I was hungry. This site has actually helped me develop those skills, and they are very useful. Reading your blog, you no doubt understand this aswell.
It might be a bit early to ask this, but do you have an idea of how much down you are going to use in your next half quilt? My Arc AT has 6 oz or so.Apr 13, 2009 at 2:36 pm #1493703
If you and I are dating the same woman, you (I?) have some s'plaining to do.
I was thinking of using at least 5 oz of down. This number is arbitrary and based only on a one ounce overfill on an Arc AT for my size (I'm 5'6"). I will probably use no more than 6 ounces, as more than that requires that I buy an additional 3 oz from Thru-Hiker. Using 5 oz and buying 6 oz also permits for a large fudge factor.
This is 4000 cubic inches of down, uncompressed. I intend to use 1/2 to 3/4 in baffles, or maybe even sewn-through construction (using Dixon Double Bivy or MLD SuperLight to mitigate cold spots). I have not run the numbers to determine down density, yet.May 6, 2009 at 10:30 pm #1499616
Jason BrinkmanBPL Member
I would suspect the problem was definitely the MB Down Inner Jacket. That amount of sewn-thru loft would not keep me warm for 30's with only a capilene 1 and windshirt.
Was the windshirt over or under the jacket? I would think over the jacket would be warmest if the windshirt is big enough to not compress the down.
Some elephant foot bags go up nearly to your armpits, which would double up the insulation on your torso. Might be the most efficient way to add loft without significantly more weight.
Also, my feet are the first thing to get cold when I push the limits of my sleep system too far. I have observed the exact same thing as you – slightly chilled overall, and can't pinpoint a cold spot, but feet are uncomfortably cold.May 6, 2009 at 10:38 pm #1499617
Ditto the above comments. The montbell inner isn't warm enough for sleeping in down to freezing IMO. For a sleeping quilt you want around 2 inches of loft to stay warm at that temp (a bit less if you're layering underneath) and my montbell inner has nowhere near that. Standing around in camp, ok, but sleeping: no way!May 7, 2009 at 5:13 am #1499649
@mn-backpackerLocale: Land of 12,000 Loons
I think it's the MB down parka as well. I went for a walk this winter when it was 30 degrees out wearing a smartwool microweight long sleeve and the MB down parka only. I was just warm enough – perfect – while walking. I'd probably be fine around camp with a wind breaker. I don't think I'd be warm enough sleeping in it at that temp. I'm pretty sure I'd get cold.
While it's extremely efficient for the weight, it is only 2 ounces of down, and your torso looses way more heat than your legs.
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