I've made a hammock sock that (with small modifications) could be adapted to most any bridge hammock, including (in particular) the JRB one. As the JRB BMBH is shipping now, I thought I'd share my design. In its simplest form, all you need to do is cut straight edges, and sew straight hems.
On to the story.
I became convinced I need a hammock sock one night last month when the temperature was in the mid 30's---and so was the wind (in mph). That's not so unusual out here on the prairie.
I had adequate insulation for the temperature w/o wind, a JRB UQ. But that wind stole my warm away.
I made and reported on an earlier version of the sock, but for a variety of reasons (mostly trying to avoid starting over) that one left the endpoints of the spreader bars exposed. Trying to work around those was a pain. When I made a new bridge hammock I figured it was time to redo the hammock sock.
This time the sock would contain the whole hammock, spreader bars and all. The pressing question was how to shape the fabric around and bring it together past the spreader bar. Happily it turns out that a simple pattern seems to work.
The end product is a big tube, 120" long, and 120" in circumference. Each end of the tube has velcro (I use Freemagic) on opposing sides, so you can seal up the tube end in a 60" line. When you seal, you end up sealing around the suspension lines.
Here's a diagram of the fabric used. Dimensions shown are the finished ones that work for a bridge that is 7' long from end-cap to end-cap.
The basic concept is to take full width roll of silnylon, cut a length that when hemmed is 120". Cut it down the middle in the long dimension. Hem or use bias tape on all the edges. On both pieces sew on a 120" strip of one-sided velcro (like FreeMagic). These two pieces are the ends of the sock. Being sil they provide waterproof coverage in the normally exposed directions.
The sock has a 60" x 60" top, and 60" x 60" bottom (both dimensions when finished).
This is a lot of fabric, compared with socks for normal hammocks. But it is necessary, if you are to cover the whole hammock---particularly covering the ends of the spreader bars. For the mathematically inclined, I can model the "width" requirements of the tube before the the long edge is sewn up as the circumference of an ellipse. The long axis is a tad over the length of the hiking pole, say 40". The short axis is the height; the hammock can drop to almost 18" below the spreader bar, so make the short axis 36". The circumference of an ellipse with those dimensions is approximately 119.5". So there you are.
I wanted this sock to create dead air, and also protect the ends and bottom of the hammock. A bridge hammock is wider, lower, than other hammocks, and so the normal hex style may expose hammock ends of a bridge where it would not for a normal hammock. Thus I opted to use silnylon at the ends, and at the bottom of the tube, and use breathable DWR ripstop nylon above my body. Conceptually you sew together the pieces in the orientation shown in the figure above, then sew the top and bottom edges together. Instant tube.
It would work to make the sock a simple tube, and have entry and exit require one to undo the velcro at the head end and slide the sock out of the way. That's a hassle though. I have a 8' long double tabbed zipper to press into service. There is a weight penalty of a few ounces using it, but it is also a convenience. I embedded it in one side of the top fabric panel. When closed up there are zipper tabs up near the ridgeline, at both ends of the top piece. Either one can be pulled down, so this is an easy way to get some ventilation. I can also get ventilation at the sil end caps by not tightly sealing up the velcro there, in some small spot.
Because of my DIY bridge design it is easy for me to get it on and off the hammock just by disconnecting the suspension triangle from the ridgeline and slide the sock over the body. It might not be as convenient to do this with the JRB hammock though. There are ways one could alter this design though to accommodate, mostly involving additional cuts, and more velcro.
Because of wind it was hard to get good pictures this morning. I'm in airports, conference rooms, and hotels all week. Not sure when next I'll get the rig up for pictures, so will share what I have at the moment.
The bridge makes a pretty good sail. The orange line is suspension ridgeline, I've got tabs and lines up from the sock body so I can suspend the top. You can see th U shape of the 8' zipper, that starts at sock ridgeline, drops to be close to the lower body of the sock, then rises up again to the sock ridgeline.
Here's a view of the sil endcap closed up.
Here's a view of the sil endcap opened up.
oh yeah, it weighs 21 oz. For the fabric alone in the dimensions I've posted the weight would be 16 oz. if I used 1.1 oz fabric for the top part of the body, and sil weighs 1.3 oz the weight would be 14 oz. I used 1.9 oz ('cause I had it), there's the zipper, and some velcro (I actually cut 1/2" wide strips in half to create 1/4" strips, to save weight there).