It’s almost been a year since I drew up these plans for a hammock bivy and I thought I might as well publish them. During this time there were a few hammock bivy projects popping up, including the Kickstarter-funded Alpine Hammock and the MMG Bivy Hammock. This is truly a do-it-yourself project; I’m just waiting on some free time to sew this one up, but if you beat me to it, send me some photos!
One of the major appeals for a “convertible” hammock is for those times when you are above the treeline or in an area where trees are scarce or non-existent. Of course, any hammock can be pitched on the ground in these cases, but the bivy design takes cues from bivy sleeping sacks that minimize or eliminate a tarp, relying on a waterproof shell for weather protection. Another advantage or goal of a bivy hammock is simplicity, and it follows that it would be lighter, at least in theory.
One challenge with bivy sacks in general is breathability. Anything truly waterproof often suffers from poor breathability, resulting in increased condensation inside the bag. Improved fabrics from GORE-TEX and eVent help make this possible and are getting better all the time.
The design I drew up is a hybrid design to maximize modularity. One goal was to use a full-size hammock, opting for a longer length and shorter width for increased comfort in hammock mode. I designed the bug net “window” to be larger for better breath and moisture management. The minimal tarp is designed to pitch in different ways depending on which mode the shelter is used. An inner pull mechanism, like on my HUG bug net design, allows the occupant to adjust the tarp tension and to increase or decrease the space inside, allowing for more air space and theoretically limiting condensation.