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  1. #1

    String hammock asym mod

    I recently modified a cheap $5 string hammock to make it asymmetrical. The result was a substantial improvement in comfort and for negligible weight gain. There was one major problem (durability), but I'll deal with that in the second post of this thread.

    First, I started with a basic, off the shelf all-polyester, woven mesh hammock that I bought in a camping store for about $5. The manufacturer said on the box that it weighs 5oz and it packs into a small ziplock sandwich bag.

    It's comfortable enough when used normally, but I wanted to either add a spreader bar or make it asymmetrical to open it up a bit and make it a bit flatter.

    Adding a spreader bar would require cutting the attachment rings and I already found it a little unstable and hard to get into, so it made sense to go asymmetrical.

    I made it asymmetrical by making two six-point line groups in the HH asym side anchor positions. I rigged this from doubled waxed polyester #4 Marlow whipping line.

    My first attempt used only one attachment point. This worked fine for a while and then eventually snapped when I got in in a clumsy manner one time.

    My second attempt spread the load among six attachment points, more or less as below. Notice that the inner lines are shortest and the outer lines longer? That's because the hammock forms a corner at this area. I had to tailor the length of each line by finding the length that maintained equal tension on all lines.

    Actually, it was slightly different to this picture. I tied off on only one line of polyester. I was sitting in the hammock and moved slightly, and there was a tack... tack... tack... tack sound. That was the sound of knots popping off one by one.

    What had happened was I had applied a transient load from one side, over-stressing the outer hammock net knot, which failed and transferred the load to the next and the next, ripping each one in turn.

    I temporarily solved the solution by tying off on two hammock lines. The added strength worked fine and there were no further failures.

    I added an adjustable structural ridgeline and that took a bit more stress off the asym anchor points.

  2. #2
    I figured there were a couple solutions to the sequential line failure problem. Essentially, I need to absorb shock and spread the load among all points in a dynamic manner.

    One solution would be to replace the paracord line I was using as a guy line with elastic as the HH does, and to replace the fixed length attachment cords with one line that runs backward and foreward through a ring, to allow each line to dynamically auto-tension. That's theoretically easy, but in practice it's easily tangled and can still lead to failure.

    A better solution is to use elasticated attachment lines. This accomplishes shock absorbance and dynamic load spreading and is less prone to tangle. I went with 4mm shock cord, which is a bit of overkill, but I don't want to reach the elastic limit, because then the full force is transferred to that point, which fails.

    Adding plastic hooks has several advantages. I can move the attachment points, gather one or several lines, switch hammocks, and the clips have a tendency to let the lines slip before the net mesh fails.

    The big problem I had to solve was the means of tying off the shock cord. Shielded elastic is one of the most difficult lines to tie, because knots stretch and roll. There is a knot called the Angler's loop, that ties in shock cord, but it would have made the rigging bulky. The lighter and cleaner method is called stitching and siezing and that's what I did. Again, I used Marlow No4 siezing line, because that's what I had to hand and that's what it's meant for.

    I have not yet had a chance to hang this rig, let alone take photos, but I expect it'll work fine.

    The result of going asym on a string hammock is that it opens the hammock out a lot, makes it a bit flatter, much more stable and easier to enter and exit.

    I'll post more when I have something to show you.

  3. #3
    Incidentally, the rig you see in the second picture weighs 20g/ .11oz. I've also just weighed the hammock properly and found it weighs 6.8oz, of which the heavy steel suspension rings account for 2.3 oz.

  4. #4

    Up and hanging

    I tried it out and the weedy little plastic clips failed almost immediately. I replaced them temporarily with very small 18lb test cable ties to show you how it hangs.

    Here's the lines attached

    Here they are dynanmically taking up tension

    It hangs almost identically to a HH Asym

    Here's my hairy legs in the hammock

    It's comfortable to lie in, more stable and breezy and very light to carry.

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