I've been inspired by the underquilts display by HF members to make one myself, for warmer weather. It took way longer than I imagined, but it's done. It's 3/4 length, with a differential cut between the layer next to the hammock body and the outer layer. Thus, like the Snugfit or others that HF members have constructed, you can't get compression of the insulation when in use. I borrowed lots of great ideas talked about in HF. This is truly a product of the HF collective wisdom.
My objectives are low weight and high compression. Both of these argue for a down quilt. I figured I could take advantage of a couple of features of my bridge hammock to reduce the weight over that of a commercial quilt. The quilt I just made weighs 10 oz; I compare that with 20 oz for a JRB Nest and 16 oz for a JRB Stealth (both of which I own). I have some momentum-90 for my next one, that will bring the weight down further. I started off on this one as a practice version using some 1.1 DWR I have. The practice version turned into a real version along the way, as I realized how long it was taking. Lots and lots and lots of measuring and pinning involved here!
First, an underquilt for a bridge hammock can be narrower than those for other hammocks, there are no diagonals involved (I imagine the same is true for Claytor and Clarks, since the approach I read about most often is to lie centered). Second, I can attach the quilt to flat-fell seams on the side of my hammock body, and dispense with suspension cord. The way I do this I'm not saving weight, but its a clean solution to attaching the quilt that I wanted to try out.
I did the math on whether a relatively thin quilt with baffles would be lighter or heavier than one with sewn through seams. The comparison depends on all kinds of factors, but for my intended dimensions it was pretty much a wash. So a sewn-through version should be a little easier, and that's what I went with.
I worked backwards from the down I have. A couple of bags from Speer, each 3.1 oz of 900 fill. I looked to see how much down the Jack's various quilts have, and noted that the Stealth (a quilt I own) has 6 oz of down, and 1.5" loft. Since I was aiming towards a half or 3/4 UQ, I figured one bag of down would be about one half of a Stealth, and that's what I'd go with.
Next I figured on width of the quilt. The seams on my hammock body are 36" apart. I wanted a couple of inches on each side for suspension reasons (about which more, anon), so the width of the down-filled part would be 32".
I figured that 1.5" height for the Stealth was a pretty good guide of how much loft I wanted, and after some futzing with numbers settled on 48" length. This gives 32x48x1.5 = 2304 cubic inches of volume if I were to be using baffles. 3.1 oz of 900 fill down expands to 2790 cubic inches, so by going to 48" I'd get about 20% overfill. Close enough.
Next choice was number of chambers. This is a differential cut to be sewn through, which means that the top (outside) piece is wider than then bottom piece. All the space for the down to loft in would be created by the difference in width between the top and bottom pieces in a chamber. Now when you think about it, you see that the more chambers you use for a given desired volume, the wider the top piece has to be, because with every chamber you bring the top piece height to the height of the bottom piece; said differently, the top piece makes the walls of the chambers, so the more chambers you have, the more walls you have, and the wider the top piece has to be.
Six was a good point for balancing the need to be able to get my hand in there when stuffing, evenly distribute the down, and manage the amount of extra fabric I'll get on the top piece of fabric. That means that the bottom of a chamber is 32"/6 = 5 1/3" wide. Aiming for a volume of 2304 cubic inches, it also means that each chamber is 2304/6 = 384 cubic inches.
The next problem is to decide how much fabric should go on the top part of the chamber in order to get 384 sq inches. This is really a two dimensional problem.... if I consider the cross-section of a chamber, I'm deciding on the length of fabric that should be above 5.3333" in order to get a cross-sectional area of 384 cubic inches / 48 inches (length) = 8 sq inches. If the shape of a chamber could be a rectangular slab, then to get 8 sq inches with a 5.333" base I'd need two sides, each 8/5.333" in height, with the length of fabric of the top piece being 2*(8/5.333)+ 5.3333 to account for the two sides and the top. But the shape won't be a rectangular slab, it will be some shape that the expanding down defines. What shape should that be????
For a variety of reasons I thought that the top piece of a chamber would be essentially radial (part of a circle), and wrote a program to figure out the details. In discussion with Schneiderlein in another thread, he floated the idea of using a parabola rather than a circle. I tried that also, and it works out to be pretty close. I'll spare you the math, in the end I used 7.25 inches for the top part of the chamber. That means that (excluding seam allowances) the width of the top piece would be 6*7.25 = 43.5 inches.
On the head and foot ends of both pieces I alloted 1.5" inch seam allowance for a 0.5" roll hem. On the sides I added more---2"---because there I'm going to do a flat-fell seam to work in another piece for the suspension.
Here's a picture of the quilt during construction, with the sewn-through seams. You can see the extra material of the top (black) part.
Now to close the end I fold in the edges of the top piece on the sides, essentially aligning the middle 5.333" of the top piece with the bottom piece.
Here are the folds pinned in.
Now Dutch is a smart and observant guy, and if I didn't mention the next thing he'd ask about it. There's a black piece of fabric under the green one. What gives??? On both ends I attached a narrow piece of black fabric so that when I do this roll, two things happen. One is that the unevenness of how my pieces came together is hidden, the other is to make the roll black, not green.
So now I've hinted a couple of times about a "suspension" piece on the side. It is micro-mesh spandex, like the Snugfit uses. I don't really intend that it be an integral part of pulling up the UQ to the hammock like the Snugfit---that's actually not needed on a bridge. Rather, since I'm going to directly attach the UQ to the hammock body, I wanted something on the UQ to "give" to allow for errors in my measurements, and stretching of the hammock body. So I've taken a doubled over piece of the micro mesh (6"), the ends of which go into a flat fell seam with the edge of the UQ (which takes up 1"). When finished and laid out, the distance between the outside edge of the micro-mesh on one side and the other is 36". I finally edged the outside of the micro-mesh with bias tape. Then on the bias tape, at 1' intervals, I sewed a hook. At the corresponding point on the hammock body seam I sewed a loop. This is an idea that Dutch introduced me to, and I've been waiting for a chance to use it. I was really happy that I could use the machine to do a bar tack to attach these things, because there are 10 pairs of them!!
Here's some shots of the finished product on the ground.
And in the air
It is snugged up uniformly on the hammock side as I'd hoped. I'm going take it out for a test sleep tonight (temps in the mid-30's).
Grizz
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Originally Posted by Schneiderlein
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