Aug 10, 2006 at 5:19 pm #1219257
I had some spare sil and dwr ripstop and was thinking about a bivy that was made for a quilt (i.e. no hood).
Depending on the weather, I plan on using my headnet, wpd jacket hood and/or balaclava. All go inside the collar of the bivy which has a draw string closure to cinch everything snug. No critters getting in this bivy.
Weight: 5.8 oz (in silnylon, imagine how light in spin or cuben?)
Size: 36″ shoulder X 30″ foot X 82″ long. The footbox is a little wider than necessary because originally it had a drawstring closure down there too, but I decided to remove that.
Fabric: 1.3 oz silnylon floor, 1.1 oz dwr breathable nylon ripstop top, both cut same size. All seconds from OWF.
Options: (4) Four 1/2″ grosgrain webbing tieouts near top and bottom. Boxed foot area to ease pressure on bag loft. Spectra 2 drawstring collar with micro barrel lock.
Cost: $25Aug 10, 2006 at 9:40 pm #1360898
@crazypeteLocale: Above the Divided Line
So you put your head on the dirt??Sep 9, 2006 at 11:08 am #1362712
Bill FornshellBPL Member
@bfornshellLocale: Southern Texas
Your design is fine. We always have something we can lay our head on to keep it “out of the drit”.
“Weight: 5.8 oz (in silnylon, imagine how light in spin or cuben?”
For your size bivy I figure you used about 2.08 sq yards of material for each the top and bottom.
Using a really good material for the top with a true weight of about 1 ounce per sq yard and Cuben for the bottom the material for a Bivy like yours needs about 2.61+/- ounces of fabric.
The really big difference will be in the cost.
Top – Momentum 90 (about a true weight of 1 to 1.1 ounce per sq yard) from Thru-Hiker at $11.95 a yard (need two yards with a seam or 3 yards without a seam). Cost with shipping maybe $30 – $42.
Bottom – Cuben ( about a true weight about .35 to .44 ounce a yard) (need three yards) from Cuben Corp at about $17 a yard. Cost with shipping maybe $51.
Total $81- $93 for a bivy that weighs about 2.65 ounces with a cost per ounce of about $31 – $35 an ounce.
If a person got lucky at Wal Mart the material for a bivy this size (5 yards) might cost less than $6.
Cost of Wal Mart bivy maybe $6 and a weight of maybe 6 to 8 ounces with a cost per ounce of about $.80 an ounce.
A 2.65 ounce bivy is below the SUL catagory and I don’t think it will ever be cheap to get there.Sep 9, 2006 at 11:56 am #1362715
Thanks Bill, as always well thought out and kind comments.
Yeah the cost is more for SUL but hopefully soon the good fabrics will be avail for us one off-ers.Oct 28, 2006 at 2:09 pm #1365705
After my last trip I made two adjustments to my bivy. The new weight is 5.5oz.
1. Preloaded 1/16″ shockcord with interior routing so it can be adjusted from inside the bivy.
The preload allows less shockcord to be used and keeps the bivy opening snug on the torso when sitting up/getting in thus keeping dirt from being scooped up by the lip. More torso protection when cooking in cold weather.
2. Tapered bivy footbox from the knees down (30″) to match my quilt footbox when lofted. This resulted in a new 22″ wide bottom before I boxed the corners at 5.25″ or 8″ across.
The new taper reduced unnecessary fabric which is normally reserved for gear storage. I don’t have any gear to store in there besides a 6×9 aloksak.
Most importantly it reduces the slip/slide area that my leg insulation can escape in. I use my pack with whatever clothes I’m not wearing as my leg insulation and when the bivy was wider I ended up on either side of the pack. Too many slick silnylon/spinnaker surfaces. Now the pack does not have any where to go.
Overall I am very happy with this approach to bivy use. Each time I use it I wonder how I could integrate the quilt and bivy into one unit, eliminating the extra drawcord. Wouldn’t be that hard really. Here’s some pics:
Sleep mode. Windshirt hood, platy 2l pillow:
Cooking in camp mode. Preloaded drawstring secures bivy around torso. Easy to get a quick sip of water when your platy is your pillow:
Detail of preloaded shockcord:
Detail of footbox:Oct 28, 2006 at 2:17 pm #1365706
@pivvayLocale: Rocky Mountains
Nice work! With an Epic top, cuben bottom and 1 layer of climashield XP on top it might be the perfect summer minimalist shelter/sleeping setup?
How did you sew the box bottom? Just like a stuff sack only bigger?Oct 28, 2006 at 2:29 pm #1365709
How’s it going? The boxing it easier than that. There are only two pieces of fabric for the bivy: the top red piece and the blue bottom. Both are exactly the same dimensions. So to box it:
1. With right sides together, (assuming you’ve done all the little stuff and you are ready to put it all together; stuff like drawstring collar and tieouts) sew the perimeter of the bivy together. I start by sewing across the bottom and then work up each side to the top. You should now have a squarish looking bottom.
2. Boxing it entails taking one corner and forming it into a triangle by bringing the bottom hem and the side hem together, like if you stood the bivy on it’s side and then flattened out that way.
3. The size of the box is determined by how big the long side of the triangle is. I usually measure 5″ for each short side (measured up from the point of the triangle at the corner of the bivy) resulting in an 8″ long side (the side you would cut off).
If you cut with a sodering iron the two pieces of fabric will be melted together making it easy to sew.
Now flip the bivy right side out, fluff and voila.
If that is too confusing, I can provide a pic.Oct 28, 2006 at 6:55 pm #1365726
@ramblerLocale: On the AT in VA
Well, I made a similar, but not so nicely made bivy with a silnylon bottom and epic top. It kept slipping off of my pad until someone suggested the obvious: “put your pad inside the bivy”!
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