Backpack destruction

There are two kinds of hunting backpacks. The first is a burly backpacking pack, with enhanced hipbelt design and some manner or provisions for keeping (boned out) meat weight high and tight to maintain load carry. Internal loops at the tops of the stays are the best option here, as building enough anti-barrel into a frame to make meat shelfing a good option necessitates a lot of weight. The second type of hunting pack is exactly that; a truly rigid frame capable of both not flexing much when loaded to 100 pounds, and resisting barreling to the extent that compression between the pack bag and frame requires.

The first type of pack is best suited to true backpack hunters (i.e. those who don’t just pack in 3-10 miles to basecamp), especially those targeting critters in the deer/sheep category, namely animals sub-300 pounds live weight which when carefully boned and fleshed can be packed out in one trip by a reasonably fit and experienced hunter.  Bare pack weight can be in the 3-4 pound range, and framing can be flexible enough that load carry in the 30 pound range isn’t overly restrictive.  1/5″ by 3/4″ thick 7000 series aluminum is my standard here; much thicker and you get into back brace territory, go down to 1/8″ and load carry above 60 pounds gets too wippy/bouncy.

The second type of pack has a few keystone examples worth discussing.  Kifaru’s combination of wood/carbon laminate stays and 1/8″ HDPE framesheet enjoys continued popularity, the current Duplex Lite being the most recent version.  This combo is effectively vertically rigid under practical hunting loads (>150 lbs), and nicely resistant to barreling.  The enduring popularity of the Duplex is, in essence, that it mimicks the rigidity of a modern external (like the Barney’s) with a narrower and in some cases shorter form factor.  Folks packing a lot of elk, especially in a guide or bro/gang hunting capacity, are well served by such a pack, as are midwestern eHunters who primarily pack dreams, climbing treestands, and sacks back to the feeder, not necessarily in that order.

As a final prolegomena to the title content I ought to mention the Seek Outside frame, as I’ve spent a lot of time under a Revolution, and because the system does a decent job of spanning the gap between the two types here discussed.  The Revolution variants (and the Brooks, which I haven’t used) do a good enough job of fighting barreling.  They are also pretty darn vertically rigid, while still being lively enough when lightly loaded.  The problem is in the bulk of the frame, though given that nothing else currently comes close to this compromise that is a small price to pay.  My trepidation is in the long term prospects of the tubular frame.  After my elk pack out last fall I hosed down my frame, let it dry in the sun over the odd Thanksgiving heat wave, then put it in the closet until April.  When I pulled the frame back out a asymmetry to the bends was unmistakable, and this in the older, heavy duty frames with thicker walled tubing.  I bent the tubing back and used it since without issue, but worst case testing does make me worry about this, long term.

Worst case testing is a useful and very fun exercise, especially if it involves a big pile of stuff your boss paid for wholesale.  Perusing the comments of the GoHunt video is interesting for a couple reasons; it exposes the rampant bias seemingly inherent in users of hunting packs, and displays the faith the Kifaru tribe has in their product of choice.  I have no doubt Kifaru would survive a comparable test well, and given Kifaru’s well documented record of rather imprecise (nice way of saying sloppy) stitching and build standards, it is worth investigating why I think so, contrasted with why Kuiu failed the test so thoroughly.

That the Badlands et al. class of packs ripped and broke should not be a surprise to anyone who has taken one off the hook at an army surplus store.  Generic fabrics and zippers don’t cut the mustard for heavy loads, nor do 6000 series aluminum stays, unless they’re thick enough to also be massively heavy.  My only shock here was just how much those three packs cost, a thought which quickly flowed into wondering why anyone buys them, when you can get an Aether Pro for $375 off the shelf.  Real expertise is not needed here; if a material feels cheap and weak, it probably is, and sentiment will not change that.  I wasn’t surprised at the widespread zipper failures either.  Tearing a #5 slider off the coil isn’t a fair metric, but zipper ends which aren’t either tucked into a seam (like the Metcalf) or reinforced extensively with bartacks and multiple layers of fabric are ripe for failure, and should be avoided.  The dual front spotter/accessory pocket arrangement Kuiu has been using for almost a decade (and copied from Arc’teryx), is an ideal example.  Zipper tape that isn’t #10 is not that strong, and all too often neither are the stitched corners used to install it.

But stitching on a backpack should never, ever fail before the fabric around it.  Any poltroon with a $80 machine from Joanne’s can use anything stronger than nylon embroidery thread to put seams in 500D Cordura that will hold and tear from stitch hole to stitch hole, or in parallel with said stitching.  Kifary is salient here, they don’t use espeically tight or neat stitching, but they do use thread which is strong as hell, which allows them to systematically substitute very hasty quad-passing for bartacking, and still have products which are tougher than anyone who will ever buy them.

Which bring us to broken frames, and perhaps random questions which accompany them.  How much stronger would the Stone Glacier Krux (flat carbon rods) test in a lab, relative to the XCurve (tested in video, carbon rods with titanium joints)?  Are the Mystery Ranch stays actually carbon, or the glass/carbon composite of the NICE frame?  Can someone actually make a curved carbon and/or composite pack stay which is stronger, functionally, than aluminum?  Quite a few have claimed as much, but every example either breaks in my hands or those of others.  Given that the Kuiu frame GoHunt broke is the upteenth, updated version, after the company went through a number of dramatic, public failures, it’s hard to get excited about not-metal in this application.

I’ve broken lots of packs, especially over the past 7 years, when investigating particulars about fabric and design has become a hobby, and occasionally job.  Almost all of them have been through abrasion, generally in the lower third of the pack.  Sawing the lower shoulder strap webbing in half while canyoneering has also happens several times over.  Aside from this, and longer-term point pressure issues in suspension components (as detailed in the Evolution frame review mentioned above), all my pack failures have been induced through hyperbolic, abusive, artificial testing.  It might take 40 or 80 field days to either fatigue one of the those composite stays to failure, and absent access to a private lab machine, the only pragmatic way to accelerate the knowledge curve is to chuck it down a cliff.  This way you learn about the stay, suspension design, and pack material, all at once.  I’m not saying that I’d have many hesitations about taking a Stone Glacier or Seek Outside pack into the field, just because it might fail under barstool lab testing, and I’m certainly not willing to buy into the heavy hipbelt and “yoke” system Mystery Ranch uses.  But the kind of durability the Metcalf evidences in the above video is what every pack designer wants to see in their product, and I would refuse to believe otherwise.

11 responses to “Backpack destruction”

  1. I still have to add more articulated thoughts on biking and rural communities, but this is a simple one to say. The benefit I see in the SO frame is the design. One could sew a new encasement, and, push comes to shove, one could buy some appropriate tubing (maybe in titanium alloy? do they exist?) and go to a metal worker and get the frame done. As much as I wish SO to prosper, the frame is something that could be made by anyone who can be bothered to. I find the simplicity and quality of the SO frame design liberating. As soon as we move back to Finland next year I will get a sewing machine and make my own encasement. If the tubular stays ever need replacing I am positive I can find someone to sort that for me (technically one could get the tools and learn how to bend pipes). The SO frame is elegant as a design object, but more so, it is approachable and reproducible. All stuff fails eventually. Stuff that can be replaced locally (locally being one’s own home) is what I think things are at.

    PS when I say making the frame locally, it needs not be a perfect replica, but two bent pipes joined in a way that lets them rotate, and a way of stacking more pipe at the top are within what any metal shop can do.

  2. I don’t have a ton of time under the SO, but outside of the general bulk of the frame, I find it as comfortable as any of the internals I’ve worn in terms of the freedom of movement it allows.

    With the bend you found in yours, any ideas what caused it? I mean do you recall it being unevenly loaded or I was thinking since it’s once side it sounds like it could come from setting /dropping the pack down on one corner regularly.

    At any rate, for what I do, thankfully durability for me is mainly a question of the fabric and construction holding said fabric together. I would like to backcountry hunt one day (or rather assist on one as I think the experience would be neat), but such an opportunity is a long way off so hauling huge ass loadz like that and stressing the frame isn’t a big deal.

    While a lot of people were complaining about the testing too, I do think one interesting aspect of it is the dynamic, quick shoves and squishing he was doing. Dynamic stress like that, from drops or tumbles or throwing the pack are going to generate much higher forces on a loaded pack that slowly /statically picking up even 300lbs (thinking the SG test) I would guess and probably on very specific points of the pack as opposed to it’s overall strength.

    Pretty impressed with the MR too I have to say. I have their Scapegoat daypack, and while it’s heavy ass beast for it’s size, it does reek of strength.

    1. My best guess concerning the bend it that on at least one, and probably several, occasions I thumped it down reasonably hard while the load of meat was elevated a few inches above the top of the frame. Only the frame made contact with the ground, and presumably that gave it a bit extra leverage.

      1. Yes, that is the kind of thing I was trying to describe. But, an ideal frame could handle that I suppose. I’ve never carried over 50lbs in a pack, and not for long, so I can’t really say, but I imagine setting 80+lbs down gently every time is not easy.

        1. Interesting point — I was wondering whether increasing the section of the frame (same thickness) would improve things without affecting the weight too badly (there would be some weight increase at the pipe is bigger and it takes more material to actually make it). In fact I am pretty sure that is the case, after all don’t they make oversized tubes for mountain bikes for this reason? all the stuff I can find online does support this idea: make the frame of a larger diameter keeping wall thickness the same (I would really go thinner for titanium, maybe). Should I ever need to build the actual frame and not just the encasement that would be an option worth exploring.

  3. “Generic fabrics and zippers don’t cut the mustard for heavy loads…”

    Or for repeatedly being drug through cat’s claw. I’d love to see someone look into how different fabrics hold up under all the different types of “abrasion.”

  4. Ok, I did some more digging. The elasticity module of a pipe is proportional to external diameter D_e and the internal diameter D_i. I really cannot figure out how to post a properly formatted formula, so I won’t, but I did some calcs on the old style frame, that show that keeping the same thickness and increasing the diameter of the pipe by 25% one would see almost a perfect doubling of the elasticity module. Obviously two caveats: (1) the pipes would need to be bent hot and filled with sand to keep any deformation out of round to the minimum; (2) users should not, ever, bend the frame to avoid weakening it (unless they use proper tools and seal sand in the frame). Bending the frame cold and hollow would compress the tube, and set it to collapse at that point in the future. Assuming someone cares to build this bigger diameter frame one would still need to test how much stronger it is in practice (and how much heavier), but a back of the envelope calculation suggests it would be much harder to misshape in use. Whether users in general would find larger tubing palatable is a different matter as well (I would, but that’s me).

    PS keeping the diameter as is and doubling the wall size would basically give the same increase in elasticity module, but at a higher overall weight.

    1. Good to have numbers behind what makes intuitive sense. I was always a big fan of the larger diameter first generation frames; it just feels better.

      If you or anyone produced a comparable rig with the joint at the bottom you might be violating the patent Nate Coleman has on that design.

      1. This is a fantastic piece of information! I do not plan to ever make backpacks but there are a few patents out there that are pretty interesting (the SO frame is patent US2015/0076195A1). In a few years time it will be possible to sell backpacks with the most amazing features, all detailed in these patents — or not. Patents show how conservative manufacturer are: the patent for load lifters independent from the shoulder straps that McHale invented is expired and anybody could now just use this design, but nobody does.

        1. Trivia: looking at backpack patents, I discovered that a backpack maker (still in the market) owns the patent for the meat shelf that is seen in a number of its competitors. The patent is still valid, and will be for another 12 years!

        2. Funny. Heck of a specific thing to patent.

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