Friday, July 27, 2012

Ultralight hammock

We see a lot of posts on lightweight hammocks and we are in the market making them. So here's a breakdown of what we've done and a brief explanation of how we've done it.

I don't own a Grand Trunk Nano 7, but I have purchased other GT products and find them exceptionally well made and affordable for what you get. Bottom line, I think that brand offers a great mix of quality and value. But the Nano 7 has a reputation of being a very light, uncomplicated hammock. Again, not owning one, I learned from reviews and specs that it was a 7 oz. hammock and that weight included suspension hooks and channel loops.

We've touted BIAS as an affordable entry into ultralight hammock camping and the challenge seemed too tempting to pass up.

All of our hammocks, since our early incarnations as we entered the market, have been 11 footers. We learned early on in our hammock making tests that long seemed to "lie" a lot better than short and the length made the need to lie on the angle a lot less necessary. We found, in short, that long hammocks eliminate the need for wide hammocks. This proved interesting.

A nine-foot hammock that's 64 inches wide brings, in theory 6,912 surface inches. Some of this is lost in the end taper and the gather, but let's go with that math for the moment.

Take an 11 foot hammock that's 52 inches wide and run the math and it comes to 6,864 surface inches, with the same caveats about loss in the taper and gather applying. So, if the fabrics are identical it stands to reason that the 11 foot hammock will be lighter thanks to the reduced width. The question becomes, "Is it as comfortable?"

Comfort is anecdotal and no two people have the same "sleep number" as an astute hammocker noted on a Hammock Forums thread. What we found was that, yes, the 52-inch hammock with the extended length was far more comfortable than the shorter, wider hammock.

Taking that logic to our approach to how to build a hammock that would fare well with the Nano 7 proved enlightening. First, we found a lighter fabric. Using a sub 1.1 oz. military grade 30 denier nylon ripstop, we got our hammock down to 6 oz. True, this isn't "apples to apples" on the Grand Trunk because it includes hooks. The function of the hooks, though, is to connect the hammock loops to a suspension system. A toggle has the same effect. It connects the hammock to the suspension. At 5 grams per pair, our aluminum toggles bring the finished weight of a Weight Weenie Micro (our name for this long, short, light hammock) to about 6.17 oz. Exact weights vary a little based on the hand-crafted construction of our hammocks, but this is very close based on our design.

So the question becomes did we succeed?

Well back to this "apples to apples" approach... We're still not there. The main reason is that the GT Nano 7 is 9 feet long and 4 feet wide. So to compare "apples to apples" we'd have to shave four inches in width and two feet in length off our Weight Weenie Micro.

And there you have it. We have produced a lighter hammock (seven ounces vs. six ounces) with greater surface area and (anecdotally speaking) more comfort because of the increased width and length.

The stats:
Finished Width - 52 inches
Finished Length - 132 inches
Hammock weight (with loops) - 6 oz.
Hammock weight (including toggles) - 6.17 oz.

GT Nano 7
Finished Width - 48 inches
Finished Length - 108 inches
Hammock weight (with loops and hooks) - 7 oz.

-- Brian

Sunday, July 22, 2012

Hammocks: Double Layers vs. Single Layers

We often get quizzed about the difference and purposes of double layers and single layer hammocks and this post is designed to cut through the red tape and get to the heart of the matter.

First of all, we see two main purposes for a double layer hammock: 1) warmth and 2) support.

Let's get to brass tacks. Warmth. Warmth is a huge concern of hammock campers who suffer from convective heat loss. This essentially means that air is circulating around you and there is no accumulated warmth below your body. Keeping your back warm is critical to hammock comfort.

The mistake I made -- along with almost any other hammock camper who started out -- is that I thought a sleeping bag would work fine to keep me warm. Not so.

A sleeping bag is a nightmare to enter in a hammock with all the writhing, wriggling and tossing necessary to get it under your back. Additionally, the compression of the loft in a sleeping bag causes the insulation barrier to hold in the warmth to become thin. Paper thin. It doesn't take long before you realize that a sleeping bag won't do in cold weather. While you may be willing to tolerate it on cool nights, most folks find it's a real hassle to deal with for the benefit it provides.

An aside: the purpose of "loft" in a blanket was something I never thought about. We all know fluffy means warm, but until I got into hammocking, I never thought about why. The short answer is that your body warms the the loose fibers/loft contained by a wind resistant barrier (the outer lining of the blanket/quilt). The wind barrier doesn't allow the air trapped within the fibers to circulate much. Thus those fibers get warm from your body heat and they stay warm (mostly) because of a cover that blocks circulating air/convective heat loss. With air circulating through those fibers and cold air blowing over it, it wicks away the heat. Or with no loft due to compression, the fibers can't fill with warm air which is what happens when you lie on top of a lofty sleeping bag... aside over.

The next step in hammock evolution is the closed-cell foam pad. These can be had inexpensively at big box stores and while they work great, the reality is that the comfort factor can be lacking. First of all, a CC foam pad conforms to the shape of the hammock and efforts to stretch it across the diagonal are frustrating affairs. While most campers find that it works -- and works well -- the problem with using it on a single layer hammock is that it slides around and gets frustratingly difficult to find a good sleeping position.

Enter the double layer hammock. The double layer allows you to insert a pad between the top (the layer that touches your body) layer of the hammock and the bottom (insulating) layer. This results in a pad that doesn't squirm around, that can be adjusted to the proper shape and angle of the hammock user and provides a barrier of insulation and warmth. The area where there is an opening between the layers that allows the pad to be inserted is about 30 inches long, so getting a pad in there is usually a pretty simple affair.

The final evolution in hammock insulation is the underquilt which is really a marvel that puts a high priority on light weight, comfort and warmth (particularly high-quality down UQs). But underquilts can be very, very expensive, especially for better, high quality ones. Not everyone is interested in making them or making the investment in them. And one also has to consider that no one underquilt will be perfect for all conditions. A 20 degree quilt may be too warm on a balmy night. Most frequent campers find that it takes about three underquilts to find the right zones.

So let's break it down: A quality underquilt is going to cost $150 or more. It will be adequate for a range of temperatures but no one quilt will work for all temperatures, say, from in the 20s and 30s (Farenheit) to the 60s and 70s.

A double layer hammock costs, from most suppliers, between $30 and $50 more than a standard single layer. A foam pad costs about $10-$15 at a store. Additionally, it will be adequate in temperatures at most ranges, from the 20s to the 60s. It may require a little bottom insulation, or even a reflective  blanket on top of it to reach low temperatures, but these options are inexpensive. You can add or subtract padding as needed to make it fit your needs. This is inexpensive. I have a car windshield reflector and a CC foam pad that I use together when it's cold. Both cost about $10. I can use one or the other when it's warmer. Or I can buy a thinner, lighter pad as well.

With a double layer hammock, you'd be good for temperatures in the summer and in the shoulder seasons, even into the upper end of winter nights. And the cost would be around $50-$75 (layer plus pads). Compared to the cost of a single underquilt, it's a bargain.

Additionally, a double layer offers additional weight support and can come in handy should a layer of your hammock get punctured. At BIAS, we state that a double layer will offer at least 150 lbs. of additional weight capacity, though some manufacturers state it will double. We still view the seams as the weakest link, so we try to keep our estimates conservative.

The problem is that double layers do weigh twice what single layers weigh. Almost exactly. Other than the bag, the cinch cord for the bag and cordlock that goes in it, a double layer is a mirror image of a single layer. But for the weight support, the comfort and the cost of getting insulated, it's really a good option for many campers and backpackers.

Many opt for a single layer with an underquilt, and this really is the luxury option. It's effective, but costly and is the thing many of us gradually work up to as we get deeper into hammock camping.

-- Brian