DIY Differential-Cut Synthetic Underquilt for Bridge Hammock
A few weeks ago I made myself my first-ever bridge hammock, the Rope Bridge, borrowing some features from the renown GrizzBridge Ariel. Whatever you may think of my hammock design variation, pro or con, it has been working well for me so far. For bottom insulation, to date I have been using a 3-season AHE Jarbidge River underquilt, which, despite its simple design, works pretty well when pressed into service on my bridge. However, at around 57" long it is definitely a fractional-length underquilt for me, requiring a foot pad, and at 43" wide a significant portion of its rectangular profile is essentially wasted, rising up above the catenary-cut edges in the middle of the bridge hammock. In addition, the 25F rating of the Jarbidge was just a bit shy of my expected low temperatures, so I wanted a synthetic UQ option that was warmer without being a lot heavier. It was for these reasons that I decided that I needed some more specialized bridge hammock bottom insulation, something to respect the unique shape of the bridge-style hammock body. Clearly, I was going to have to make the underquilt myself. My goal was to "Keep it super simple" ("K.I.S.S.") and design a quilt that was easy to build, cost-effective, performance-oriented, and specifically optimized for my DIY bridge hammock...
Here was my result...
Type/Rating: 20 degree F (or lower!) synthetic underquilt with differential cut
Outer Shell: 1.9 oz ripstop nylon in Multicam
Inner Shell: 1.1 oz ripstop nylon in Blaze Orange
Insulation: Double layer of Climashield Apex XL 3.6 oz (7.2 oz per square yard total)
Construction: Rectangular insulated area with catenary-cut sides and corner drawcord adjustment
Finished Size: Approx. 72" long x 32" wide (insulated area)
Weight: 26 oz (727 grams) in stuff sack
Construction Details
This underquilt is shaped for the contours of a bridge hammock and cut with a differential between the shells to allow the Ciimashield insulation to achieve maximum loft, but it wasn't much harder to make than a standard flat, rectangular synthetic quilt with side channel suspension. Here's how I did it...
1) I started with a 2-yard remnant of Climashield Apex XL 3.6, which is 72" wide, so I had a 6-foot square of insulation with about two extra inches of length after it had been cut. From this I trimmed two identical layers of 3.6 oz insulation, each 74" long by 34" wide. Expected loft for 7.2 ounces (a double layer of CS 3.6) is about 1.75", so I planned for the differential in the outer shell to accommodate a little less than that, about 1.5", so the shell wouldn't be too baggy.
2) For the outer shell fabric I had a similarly generous 2-yard run of 1.9 oz Multicam ripstop nylon with a couple of extra inches after the trim. To my intended finished quilt width of 32" I added 3" extra (2 x 1.5" loft height) for the differential; I added another 3" on each long edge to wrap up around the insulation layers in the quilt material stack when pinning and sewing the of fabric and CS together, as a sort of hassle-free "glide strip" for the sewing machine presser foot. Therefore, I added a total of 9" to my finished width and matched the cut length of my insulation, trimming the outer shell blank to 74" long by 43" wide. The inner shell, made from a remnant of 1.1 oz Blaze Orange ripstop nylon was much easier to figure; adding a 1" seam allowance around the entire finished-dimension perimeter, I trimmed the the inner shell blank to 74" x 34".
3) Instead of the typical folded side channels seen on an underquilt for a gathered-end hammock, this UQ was designed with elastic suspension at each of the four corners, aided by cat-cut fabric side extensions built into the long edges of the rectangular insulated area, which would serve to lift and snug the quilt against the contours of the loaded bridge hammock body under tension. I cut two 70" long by 9" wide strips from some additional matching Multicam fabric I had lying around. I folded each strip along its length, wrong side out, and then marked and cut a 2.5" deep catenary curve out of its raw edges. On each strip I sewed a seam up one end and along the curved edge, inverted it to hide the raw edges with the right side out, and then folded and stitched the remaining short edge shut. This gave me two strong double-layer side extensions approximately 69" long by 4" wide, to which I would attach the adjustable suspension.
4) I measured and marked 1/2" darts 6" deep on each short edge of the trimmed outer shell blank, one at the midpoint and the others 8" to either side; each of the evenly spaced darts consumed 1" of fabric when sewn from the wrong side, reducing the ends of the outer shell by the required 3" (approximately 2 x loft height).
5) While I've built a number of synthetic quilts with success by pinning the shells and insulation together and sewing with one pass, on quilts with more complex design I have taken to sewing the shells, channels, and other components together first to secure everything in its appropriate relative position before mating them to the Climashield insulation. Laying the differential outer shell right side up, I measured 3" in from the edges and positioned the side extensions with the folded edges to the outside; then I centered the inner shell blank wrong side up on top of them, exactly coinciding with the edges of the extensions. I secured everything temporarily with some masking tape (handy!) and tacked everything down with a single row of stitches parallel to each long edge, inverting the quilt briefly to check my work before reversing it again and removing the tape.
6) Next, I layered the two pieces of Climashield on top of the inverted (wrong side out) pre-assembled quilt shell, wrapped my 3" excess over the long edges, and pinned everything precisely at 4" intervals. I sewed the insulation down in a single pass on each side and inverted the quilt right side out, adding an additional row of stitching on each short edge to close up the ends of the quilt in rough fashion. To conceal the raw edges of fabric and Climashield, I folded some 1.5" grosgrain ribbon over the short edges of the quilt as finishing trim, allowing an extra couple of inches on each end to fold and mount a total for four 3/4" D-rings (1.5" ribbon folded in half is 3/4" wide) for the underquilt suspension.
7) In the final step, I mounted each of four 1/2" Beastee Dee rings to four 6" lengths of 1/2" grosgrain ribbon, folded them over, and mounted them in place on the outside corners of the fabric side extensions in line with the cat-cuts, so that under tension they would pull the cuts straight lifting the quilt at the midpoint of the long edges to keep it close and gap free when mounted to the hammock body. On each corner, I tied a short length of 1/8" shock cord in a lark's head knot to each of the big D-rings and threaded the two parallel tails of the cord though the corresponding small D-rings, finishing them off with a cord lock and a figure 8 knot. This provided a strong stretchy loop at each corner of the quilt to loop over the sewing bobbin ferule in the Rope Bridge's Amsteel hammock suspension, allowing for easy independent adjustment of the underquilt by the occupant from inside the loaded bridge hammock.
With a variety of discounted components, my total cost for this bridge hammock underquilt build was around $70, and the total build time was less than 8 hours. I could probably build it in 3/4 the time now that I know what I'm doing.
The quilt mounts easily and fits perfectly on my DIY bridge hammock, and it covers me more or less completely in the hammock, obviating any foot pad inside my top quilt. It feels nice and warm in test hangs, and there are no gaps at either the sides or the ends. The lay remains unrestricted and comfortable for the occupant. Following the long, narrow profile of the bridge hammock, the weight savings over a full-length synthetic underquilt for a gathered-end hammock made from similar materials is pretty dramatic, enough to make up for the carry weight of a full set of standard aluminum two-piece spreader bars.
Performance reports forthcoming. Feel free to comment or inquire below. Thanks for reading this project report...
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. As always nice job, top notch. I haven't ventured into bridge hammock territory ( yet ), but have always been intrigued with the design.
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Originally Posted by jellyfish
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