'Success? Failure?' Rating: ★★★☆☆
The Problem (As I See It)
I have tried out quite a number of packs in my time. The undisputed king of my collection is my Macpac Glissade - an incredibly rugged and feature-laden bit of kit. In some respects, however, it is a traditional pack, with a traditional shoulder harness and hip belt system (although the latter is articulated to increase mobility). It is also built to last a lifetime, and this is reflected in its weight - around 3kg [6½lbs] empty - and the price - ≈NZ$500. In building my own pack from scratch I wanted to see if I could address a few issues I have with such a traditional design.
My first issue is with the harness. A traditional shoulder harness consists of a pair of padded fabric straps that extend from a common anchor point between the top of your shoulder blades, over your shoulders and down to an anchor point at your hips. This configuration has a weakness in that the sack tends to pull backwards away from your back (exacerbated by any form of hip belt, which acts as a pivot point). This weakness is typically alleviated with a system of straps from the top of the sack to an anchor on the forward face of the shoulder straps. Unfortunately this system tends to pull your shoulders back, which can cause strain between your shoulder blades. This is in turn alleviated with a sternum strap, but this strap is often elasticated (to allow you to breath freely) and thus is of limited effect. The standard hiking pose (especially when walking up hill) thus includes thumbs-under-shoulder-straps in a attempt to alleviate some of the tension in your shoulders. A second area of concern for me is the questionable value provided by a hip belt. I believe most hip belt systems contribute more to shoulder tension, sweatiness and lower back strain than they contribute to any weight-bearing process. In this I am willing to concede that I may never have managed to set-up any harness I've ever used 100% correctly (either by myself, or with the help of outdoor shop Sales Assistants), but I think it is worth investigating an alternative.
My second issue is with overall pack weight. If I want to keep my total pack weight to no more than 15kg [33 lbs], then my (empty) Macpac Glissade is contributing 20% of the load. Instead of a "heavy-duty, last-a-lifetime" approach, I'd like to explore a "light-duty, almost disposable" approach, at least with respect to the sack. If I can construct a light-weight, waterproof sack that will last for a week or two's hiking (or a month, with some gaffer tape patches) for less than NZ$50, then I reckon I'm onto a winner. A related area of concern is the lugging around of lots of padding. Sure, it helps with comfort, but it is also dead-weight. What if you could strategically replace the padding with items that serve a second purpose (e.g. a towel, rain protection, fly sheet, etc.)? A bonus would be to design the pack to custom fit the rest of my gear - "a place for everything, and everything in its place" kind of thing.
My first forays into designing something better involved trying to invent a multi-purpose pack - one that doubled as a shelter or sleep system after its day on your back. I may yet come back to this idea, but I've opted for something simpler to build for now. The design I'm going to explore, and report on, here focuses on two ideas to address the two issues detailed above: a lightly padded, rigid shoulder harness system, with a sternum strap instead of a hip belt; and a separate, light-duty sack system that can be replaced easily (and cheaply). I'm aiming for a total harness + sack weight of 1.2kg (less than 10% of my ideal loaded pack weight).
I wanted a system that would hold the load close into my body without requiring strap upon strap to create the ideal load-bearing structure. I opted for a rigid frame that hooks over my shoulders. Minimal padding is provided and features like lumbar support are provided by the sack (see below). All load bearing is done by my shoulders, and no hip belt means no lower pivot point for the load, no sweaty back and freely moving hips.
My prototype was built using a pair of heavy-duty steel storage hooks, bent to shape, plus some aluminium rods. The padding is 7mm, closed cell foam, with 10mm webbing reinforcement glued on. This system maintains its shape and structure without a multitude of straps and weighs in at under 900g [32oz]. Building the entire structure out of aluminium would reduce the weight further (and could make for a more snug fitting harness). A sternum strap helps to mitigate any sack pendulum action (note the asymmetric buckle position to avoid having the buckle on top of my sternum/diaphragm).
"Cheap", "light weight" and "waterproof" were the watchwords for this piece of the puzzle. I also wanted the sack to neatly fit the rest of my kit, the largest component of which is my sleeping bag. I hit upon the idea of using a pair of fabric 'tubes', each containing a pair of waterproof stuff-sacks, to meet my needs. Each tube is open at both ends and secured with velcro cross-straps. The tubes are joined side-by-side with velcro, secured to a fabric panel at the rear (also via velcro), and with webbing straps on the front. The back panel extends over the top of the sack to contain a water bladder, and stores my raincoat in a pouch in the small of my back (in lieu of any lumbar padding). The front webbing straps secure my sleeping roll mat, which provides some longitudinal stiffening to the sack when strapped in place. Three anchor points secure the sack to the harness.
All Together Now...
And the final weigh-in? Harness + sack = 1275g [2.8 lbs]. Nice.
Test one: 6.1km/1¾ hours, easy/moderate bush walk, 18kg load
The sack was unfaultable. Everything was stowed securely and exactly where I wanted it to be. The geometry, stability, durability and load-carrying were perfect. The only (minor) issue I could put my finger on was that the sack is not a 'stuff-n-go' item - it took about five minutes to pack, assemble and mount the sack.
The harness was less satisfactory. I was surprised to find that the load placed significant pressure onto, and immediately below, my clavicles (collar bones), i.e. not onto the tops of my shoulders, but onto points well forward. This was compounded by being where the framing terminated, so a pair of pressure spots, one below each clavicle, developed fairly quickly. To mitigate this I added a 4-cm-square of aluminium and an additional square of padding under the end of each shoulder frame. This helped a great deal, but the pressure spots were still present, albeit spread over a slightly greater area. I think I'll need to re-engineer the harness to spread this frontal pressure in a better way. Stay tuned...
Enhancement Suggestions: If you have a suitable sewing machine (one that can sew trouser legs), you could make the entire sack out of a single piece of fabric - this would save a good deal of weight, but would reduce the ease with which the sack could be repaired. Building the entire harness frame out of aluminium would save a good deal of weight and might make it easier to tailor to your anatomy.
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