Hennessy Ultalight A-Sym
Weight limit: 200lb
Contact Hennessy Hammock directly: 1 (888) 539-2930
This Review also posted as part of a test by Backpack Gear Test.
The Hennessy Hammock is unlike any other tent or bivy you have ever used. It has more things you can do with it that any old tent or tarp could even begin to have. Over the last couple of years lots of people have come up with cool things you can do with the hammock and tips for its use. I have collected some here which I figured out on my own or read somewhere else and tried myself. This section will probably grow over time.
Tip #1 - The Vestibule
More to come...
Tip #1 - The Vestibule:
Because the hammock has a large fly - bigger than some tent vestibules, you can use this to your advantage. Instead of needing to carry the extra weight and bulk of a separate vestibule a tent user has to pack, just do this:
I figured this out about a week into using my first Hennessy Hammock. I used this one a lot on the rainy AT in the summer of 2001. Cooking, washing, dressing, etc. Who needs a trail shelter?
Tip #2 - The Chair:
I saw this one on the Hennessy Hammock Web site. It was so obvious I can't believe I didn't figure it out myself!
Tip #3 - Bivy Tent:
This is also one I figured out about a week into owning my hammock. I posted the original pics back in 2000, and before I knew it, the idea was all over the internet. It eventually made it to the Hennessy Hammock Web Site.
Tip #4 - The Heat Reflector:
There are a lot of different set ups for making the Hennessy Hammock work in cold weather at BackpackGearTest and at the Hennessy Hammock Web Site. My system was this: A shortened piece of an Mt Washington Evazote® foam pad. I cut it to about 40" - just long enough for under my butt and shoulder which are the areas of greatest compression for your bag, thus the coldest spots when sleeping in the hammock. Under this I added a car windshield sunscreen to serve as a heat reflector. Mine is a foam type for trucks that is about 24" or so wide, and about 6' long. The pad part is white 1/8” polyethylene foam and the reflector side is Mylar laminate which is shiny on both sides of the Mylar. I added small patches of Velcro to keep them both linked together inside my hammock. Total weight for all this is about 11.1 ounces. I've used this down to about 30° Fahrenheit with good success.
But after saying all that, I have really begun to doubt the efficiency of the heat reflector. After reading some posts from the more educated, doing some experiments of my own, and a little reflection into what was successful and why, I have come to the conclusion that the reflector would be very inefficient. Here is why:
The four main ways you loose heat are from convective heat loss, conductive heat loss, radiant heat loss, and evaporation. Heat and cold are not opposites. Heat is the presence of energy, and cold is the lack of that same energy. Heat transfers from sources of energy to sources lacking energy. Your body is the source, and the air or any objects around lower than your body temp is where your heat tries to migrate to. So in order to reduce heat loss, we must fight all these. I'll discuss each separately.
1. Conductive heat loss occurs when some conductor provides a conduit between the source and where the heat is going. Mylar actually serves as a conductor if in direct contact. Lying directly on a Mylar reflector can actually serve the exact opposite of what is intended. That is why using my reflector shiny side down has some benefit.
2. Radiant heat loss is how the heat from the sun transfers to the earth without a conductor or air currents to get it here. Basically it is heat seeing the cold spots and transmitting the heat energy. If you were to stand naked in a freezer, then you loose lots of heat from radiant heat loss. And your body is an excellent transmitter of heat which would allow your heat to rapidly dissipate. But if you were to surround your body with a close Mylar curtain, it would drastically (about 50%) cut down this heat loss - that is the theory behind the radiant heat reflector like a space blanket. Unfortunately for most of our systems, you must have space between you and the reflector, touching it negates the benefit.
But there is a better way - wear clothing. If you put on long sleeve clothing you would dramatically reduce radiant heat loss (about 98%), and the clothing itself makes a poor source for radiant heat loss (about 5% effective as your skin). To add to this, each layer you add further cuts this effect down. So by just wrapping yourself in a hammock and a sleeping bag you negate the need for a reflector.
3. Convective heat loss is from air currents carrying away the warm pockets of air your body generates - wind chill is a way to understand the effect. To reduce wind chill, you must reduce the air flow to the point where you have no large drafts of wind, and reduce the amount of tiny air flow - basically build spaces of dead air around your body. That is exactly what down sleeping bags do with their loft and the tight fit of a mummy bag. Convective heat loss is the main problem with a hammock. You have a space under you where your loft gets compressed the most, thus it is ineffective, and to compound the problem, it provides a large surface area for air to circulate around you. In hot climates, this is a huge plus for keeping cool, but in colder weather it is a large problem that must be dealt with.
The best way to stay warm against convective heat loss in a hammock is to have a thick pad under you that resists compression, is closed to air flow, and is wide enough to prevent cocooning of the hammock around you and/or also provide insulation to the sides if it does. Some heat reflector ideas are actually reducing the air flow around your hammock or body by surrounding either in non breathable materials, thus actually serving the purpose of a convective insulator.
This is supported by a couple of my experiences. In one, I used my Army sleeping bag which is made from a synthetic material that doesn't compress very well. In it I stayed very warm in my hammock down into the 30s - must be because it resisted compression. In another I slept comfortable down in the 40s with just a poncho liner and an Army foam sleeping pad with my uniform on. Besides the clothing helping create dear air, the foam pad is 24" wide, 72" long, and made from a dense closed cell foam pad.
4. Evaporative heat loss occurs when you breathe or sweat. You can't stop breathing, so forget that, but you can use a vapor barrier to reduce heat loss from your body. The best way to do that would be to sleep naked inside a trash bag inside your sleeping bag. Different people have different experiences with vapor barrier, so I won't recommend this as a blanket solution for everybody.
To summarize all this, I have come to the conclusion the reason my system worked so far is this: My sunscreen had a little foam, so it provided some insulation against convective heat loss, and since the Mylar side isn't breathable, it also provided some further protection against Convective and evaporative heat loss, but only under my body where the insulation sits. The Mt Washington foam pad and my 15 degree quilt were doing most of the work.
Based on all this information and my experiences, I believe the best insulation system for a hammock would be a 24" wide closed cell foam pad. 24" wide would prevent cocooning and/or provide side insulation in case the sides of your bag get some compression, and since it is closed cell foam, it is lighter than the self inflatable and prevents convective air flow from the pad. In colder weather, just add layers of padding. Since lighter is better, a 24" wide Evazote® pad would be best, since a 24"x60" piece should weigh about 8 ounces. A source for Evazote® pad this wide is Oware. Although the product isn't yet listed on their site, you can get 40"x60" pieces there. Another slightly cheaper option with a little higher weight is to get a Ozark Trail 1/2" Egg Crate Sleeping Pad that is 72"x48" - then trim it to the desired length.
Another option that may work would be a quilt to hang under the hammock made from down Polarguard 3D, Pirmaloft, or some other insulation. The main problems I see with this option are:
1. The quilt would be exposed to the elements such as dew and rain. It would need to have a very, very good DWR outer shell to protect the insulating material from getting wet. Using a synthetic may be more logical because it wouldn't need baffles, and if it got moisture there would be some performance advantage over down. But the the primary concern would be to prevent it from ever getting wet.
2. The weight of the quilt could be pretty high if you consider that it would need to be about as big as a Nunatack Backcountry blanket to cover the sleeping are correctly. You would basically be carrying two sleeping bags to hike with. The weight of a high end synthetic is about 2 pounds, while the weight of an Evazote pad is about 8 ounces.
3. Price. Since you are basically buying a high end quilt to go under your bag, it would be like buying two synthetic sleeping bags to hike with, while a Evazote pad only cost about $15.
To finish off this section, I highly recommend a blanket as a sleeping system for inside the hammock. Because most highly compressible loft bags do not offer any real insulation under our body, why waste your time. A blanket is easier to get into inside a hammock and your pad can serve as a draft tube if you use the old turn and tuck maneuver to cover up. I use a Nunatak Backcountry Blanket.
Tip #5 - Hammock Camp Site
A new question was asked of me so I decided to cover this here: how do you set up your campsite with a hammock instead of a tent. I think the main question is: what do you do with your gear? Not a bad question and one I can answer fairly easily.
1. I start by selecting the trees and ground. I don't always need level clear ground, but I do need trees about 10' - 12' apart that are big enough and don't present hazards (see Storm Set Up).
2. Next I pitch the hammock and set up the sleeping area. I use the standard set up procedures, this only takes a couple of minutes. Then I put my pads and sleeping blanket in the hammock so it can loft up. I use a single bag for all my clothing, and this is my pillow.
3. If I didn't already do dinner earlier on the trail somewhere because I'm stealth camping. I set up the kitchen and cook dinner. In the rain this is under the tarp, when it isn't raining this is outside the tarp. If I need to use the underside of the tarp, I use the method shown in the vestibule tip. I can use my trekking poles to lift up the fly a little or just leave them leaning against a tree.
4. All that is left in my pack by now is a few odds and end like maps, first aid kit, LED light, journal etc. I put all this in the hammock stuff sack and hang it off the ridgeline so it comes out the door of the hammock. My shoes get tied together with a quick release half hitch and hang the same way.
5. After dinner I hang my food bag with my toiletry items, pots, pans, stove, and water containers except for a small bottle I keep with me. If you check my packing list everything is accounted for except my backpack, walking clothing and rain gear.
6. Walking clothes get hung on the support lines of the hammock in dry weather to air out. In wet weather they go over the net but under the fly. My rain gear usually gets left laying in the hammock near my feet just in case it's raining when I get up, but sometimes they go in the clothing bag too.
7. My backpack is the last consideration. If I'm using a normal pack, I either put it directly under the bottom of the hammock, or strap it to a tree with the pack cover on it. For my ultralight SGT Rock's Ruck, I use it inside my hammock to keep my pad under my feet by slipping it over the end of my blanket and sunscreen pad.
Not bad! A nice low impact campsite for ultralight stealth camping. An since it's in camouflage now, it's ultra stealthy.
Tip #6 - Setting up in the rain
Setting up in the rail is simple all it requires is an extra 6' of cord. I carry a stake bag with some extra cord and my fly in an easy to get to place.
If the storm is very bad, tie it off using the Storm Pitch.
Tear down the hammock in the rain in the reverse of setting up in the rain.
The instructions for the knot on the side of the Hennessy bag can be confusing.
After some practice at doing it, this is my technique:
To make the hammock easier to tie out, I also have permanently put a loop into the shock cord. This way you just pull out the sides and stake them quickly and reduce wear on the shock cords from friction.