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  1. #1
    Senior Member GrizzlyAdams's Avatar
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    Yet Another Suspension System--the Alpine Butterfly Suspension (ABS)

    TeeDee's post on his Marlinspike-based suspension system got me to thinking...I've been using a trucker's hitch system, with a moveable SMC ring on the suspension line to be an anchor for the tie-off (on the hammock side, where there is a carabiner). Every different pair of trees I hang from involves moving that ring. Granted, it doesn't take that long, but I did wish for something where I didn't need to make such an adjustment with every hang. On the tree side I've been taking a length of webbing that has a loop on one end, and the suspension rope tied to the other. To mount I pass the free end through the loop, and the weight on the suspension cord cinches up the loop to the tree. Now I carry webbing long enough to go around sizeable trees, which means that in practice a length of the webbing (from the cinched loop to where the suspension cord is tied on) is effectively part of the suspension. However, I found on that with trees relatively close together I had to futz with the webbing to go around the tree a certain number of times, or try to get the cinch loop on the side or the back of the tree, all just to "take up the slack" in the webbing, so that I could attach the hammock with the suspension rope.

    So the Marlinspike hitch showed me the way out of this. Here's some pictures doing just what TeeDee said to do on the webbing side. Rather than trail sticks, I've cut short lengths of 1/2" dowel rod for the toggle.

    1. Here's the webbing free end, passed through the loop. My toggle is attached to the free end with a bit of cord so that I don't lose it.

    BLS-1.jpg

    2. Form a loop in the free end, near the tree.

    BLS-2.jpg

    3. Flop the loop over up towards the tree, and push up the strand beneath.

    BLS-3.jpg

    4. Slip in a toggle and tighten up.
    BLS-5.jpg

    This now gives us a place to just hook a cord on. At this point TeeDee and I part ways in the suspension, in part because my current versions of hammocks are easiest to use when there is a carabiner at the hammock ends.

    I've taken a 12 foot length of suspension cord, put a bowline at one end, and along the cord put the Alpine Butterfly knot, at intervals of 1 foot. The length from the top of the bowline to the base of the closest Alpine Butterfly loop is 1 foot, and the distance between the bases of subsequent Alpine knots is also 1 foot. This knot is described as being very strong, and as a sort of in-line bowline.
    BLS-6.jpgBLS-7.jpg

    The loops are an application to suspension cord of what Slapstraps do. The way I'll use this is to have some coarse grained adjustment of length by choosing which loop to hook over the toggle, and then fine-grained adjustment by looping the free end of the cord through the biner, back to the nearest loop, and back to the biner to be tied off---here's the trucker's hitch again, but with a built-in loop as the anchor. Another way of looking at this is that if I want the suspension cord to be N feet, m inches long, then I pick a loop to put over the toggle that gives me N+1 loops from toggle to loop closest to the biner, and then use the trucker's hitch to get the additional m inches. I won't be so detailed with the trucker's hitch in practice though. At first blush it seems a bit of overkill to make all these loops, and perhaps it is. What I get in return for doing that though, is the ability to never again have to make an anchor point for the trucker's hitch that finishes off the suspension. And in using the trucker's hitch, I can tie-off the suspension with just one slippery half-hitch. There is another benefit, as we'll next see.

    The Alpine Butterfly loops are carefully placed so that we can use them for measurement , and centering . With a known length of the hammock or ridgeline, we can get a good estimate of the distance between trees just by cinching up the hammock tightly. On one end of the hammock the suspension cord is looped over the toggle, and then one of the alpine loops is clipped into the biner. On the other end the suspension cord is looped over the toggle, and we pull the suspension cord through the biner, just to get things taut. So we estimate the length of suspension cord between hammock and tree by counting knots, and add the known length of the hammock or ridgeline.

    After making this measurement we can both center the hammock, and figure out where to make connections on the suspension cord. It sounds harder than it is. Here's an example to illustrate. Suppose I measure that the trees are 16.5 feet apart, and I know that my ridgeline is 9 feet long. This means the suspension line needs to give me 7.5 feet of horizontal separation. Divide that length by two to get the distance of the centered hammock from one end to a tree : 7.5/2 = 3.75. This is the horizontal distance though, not quite what we need---the corresponding length on the suspension cord. Sorry, here comes trigonometry, but we'll take it with a spoonful of sugar. If the angle on the suspension line is to be 30 degrees, then to get a horizontal distance of 3.75 feet we need 3.75/cos(30) = 4.3 feet of suspension cord.

    Now the spoonful of sugar. For choosing the loop to hook over the toggle, all of this that we really need is the "4". Most people are unlikely to either do trig in their head, or carry a calculator. There is however a rule of thumb that mostly works, and that is to add 15%, which most of us can do if we tip the wait staff (I compute 10% by shifting a decimal, then take half of that and add it back to get 15%.) The one important thing in the calculation is to estimate whether adding that 15% increases the unit number of feet in the length, as it does in the example (e.g., the horizontal length is 3 .75 feet, while the suspension length is 4 .3 feet.)
    BLS-8.jpg

    This distills into a pretty simple way of computing which of the Alpine Butterfly loops to hook onto the toggle :

    • measure or estimate the distance between trees,
    • Subtract off the length of the hammock, divide result by two in order to get centered horizontal distance from hammock to tree on each end,
    • Add 15% to result above with enough accuracy to determine the number of feet in length of suspension cord when hung at about 30 degrees.
    • If the suspension cord length to hammock is N.m feet, then at both ends hook the (N+1) st loop from the end w/o bowline to the toggle
    • Loop free end of suspension cord through biner, and as both ends tighten as seems appropriate.


    Pictures illustrating this last step appear below.
    BLS-10.jpgBLS-11.jpg

    You could simplify it even more by just hooking the toggle and biner at one end of the hammock and do all of the adjusting on the other, it would take a small change in the calculation.

    Admittedly limited experience so far with this has taught me one lesson. Coated Vectran 12 should not be trusted to hold an in-line loop of most any kind. I really like that cord, and this is a significant drawback. I'm using Spyderline for it at the moment.

    I'll note in passing that with a pretty simple modification this hitching system could be used with a single-line suspension. Here the biners would be afixed with a lark's head, to center their span on the rope. The bowlines at the endpoints, and the intervening alpine knots spaced a foot apart would be placed as before, continuing all the way to the biners. An auxilary piece of suspension cord would be attached to a biner, long enough to make the trucker's hitch with the nearest loop as the anchor. Bringing that loop closer to the biner causes slack in the central suspension cord between biner and anchor, and the weight is carried by the cord that brings them together.
    BLS-12.jpg


    I have had enough experience with this system to know that it goes up fast. Even without the alpine loops, the benefit of doing the Marlinspike hitch is significant. Whether I go back to the SMC ring as an anchor or stick with the loops, only time will tell. For now it was fun to work through another solution which was triggered by exposure to a new idea described here on HF.

    Grizz
    Last edited by GrizzlyAdams; 07-02-2008 at 14:57.

  2. #2
    Senior Member TeeDee's Avatar
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    Great

    Good to see yet another variation.

    About 6 months back, I tried the alpine butterfly loop method - once. Tried it with AS-78, a coated rope like the Vectran.

    I had the same problem I think you referred to with the Vectran. The alpine butterfly loops didn't hold. When I strung everything up and got in the hammock, the loops pulled tight and became smaller, much, much smaller. Got out, pulled the rope to take out the slack a little to keep my butt off the ground and got in again and the loops again pulled even smaller. Concluded that for coated rope, the alpine butterfly wouldn't work on the suspension as desired.

    I see that it works with the Spyderline. I had thoughts about that, but I had decided that I want to stay with coated and not sheathed. I just like the coated better. I think most or all climbing ropes are sheathed, so the alpine butterfly works better there.

    Good idea. Thanks for posting your idea and experiments.

    I now mark the single suspension rope with a Sharpie to mark the center of the rope, then place marks every 3" starting 5' out on both sides from the center mark. That gives me a measure of tree separation with a 6" resolution.

    When I take down, I simply lift the hang rope tied with the toggled bight to the loop over the webbing MarlinSpike Hitch on both ends. Lifting the loop off the marlinspike hitch. When I setup again, I first leave the hang rope tied to the loops with the Toggled Bight and see if the trees are close enough to the previous tree separation. If so, I have hung the hammock simply by placing the loops over the marlinspike hitch in the tree hugger webbing. If not, I can use the marks to center the hang rope with a simple adjustment of the toggled bight hitches. I no longer move the hang knots and stopper knots. Redoing the toggled bights is even easier, simpler and quicker.

    Have to find a more permanent way to mark the hang rope than the Sharpie. Maybe use different colored threads and put stitches in the rope?

  3. #3
    Senior Member GrizzlyAdams's Avatar
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    Quote Originally Posted by TeeDee View Post
    Good to see yet another variation.

    About 6 months back, I tried the alpine butterfly loop method - once. Tried it with AS-78, a coated rope like the Vectran.

    I had the same problem I think you referred to with the Vectran. The alpine butterfly loops didn't hold. When I strung everything up and got in the hammock, the loops pulled tight and became smaller, much, much smaller. Got out, pulled the rope to take out the slack a little to keep my butt off the ground and got in again and the loops again pulled even smaller. Concluded that for coated rope, the alpine butterfly wouldn't work on the suspension as desired.
    Yep. All my loops held but one. I retied it, I did an overhand knot there, I did an ordinary bowline there (weight on both ends)...nothing would hold. No coated line for this system.

    I see that it works with the Spyderline. I had thoughts about that, but I had decided that I want to stay with coated and not sheathed. I just like the coated better. I think most or all climbing ropes are sheathed, so the alpine butterfly works better there.
    since I don't have much chance of undoing all the loops I put in my Vectran without tearing the rope up, I just ordered another 100 feet of it. I'm not convinced I'll stay with the loops...

    I now mark the single suspension rope with a Sharpie to mark the center of the rope, then place marks every 3" starting 5' out on both sides from the center mark. That gives me a measure of tree separation with a 6" resolution.

    Have to find a more permanent way to mark the hang rope than the Sharpie. Maybe use different colored threads and put stitches in the rope?
    I've been thinking exactly that. Handstitch some color in the right places, putting the thread in-between the various strands of the braid.

    The toggle is great. Whatever else I do, that one is a keeper.

    Grizz

  4. #4
    Senior Member TeeDee's Avatar
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    Quote Originally Posted by GrizzlyAdams View Post
    ..

    since I don't have much chance of undoing all the loops I put in my Vectran without tearing the rope up, I just ordered another 100 feet of it.
    ..
    If you are handy with a grinder and a hand drill or drill press you can make yourself a great Marlin Spike and splicing fid real easy.. It will make undoing those knots in the vectran doable.

    Find about 6" to 7" of stainless steel tubing, 1/4" OD and about 0.035" wall thickness. McMaster-Carr is a good source if you cannot find locally.

    Use the grinder on one end to take away half the tubing making a trough as shown here.

    Then use the grinder to put a dull point on that end.

    Stick in the drill chuck, take some very fine Emory cloth and, with the tube spinning, polish the outside.

    You can use the end where you have ground it down to a trough to get into the knot and loosen the strands. The trough is great for slipping along a strand and into the knot. Once loosened a larger marlinspike like the Myerchin Marlinspike can be used to great advantage.

    A splicing fid like this can save you a lot of rope.
    Attached Images Attached Images

  5. #5
    Senior Member TeeDee's Avatar
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    Here is another view of the end showing the grinding work better:
    Attached Images Attached Images

  6. #6
    Senior Member headchange4u's Avatar
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    That's a very interesting system, Grizz. I'll try that setup next time I get out.
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  7. #7
    Senior Member GrizzlyAdams's Avatar
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    Quote Originally Posted by TeeDee View Post
    If you are handy with a grinder and a hand drill or drill press you can make yourself a great Marlin Spike and splicing fid real easy.. It will make undoing those knots in the vectran doable.

    Find about 6" to 7" of stainless steel tubing, 1/4" OD and about 0.035" wall thickness. McMaster-Carr is a good source if you cannot find locally.

    Use the grinder on one end to take away half the tubing making a trough as shown here.

    Then use the grinder to put a dull point on that end.

    Stick in the drill chuck, take some very fine Emory cloth and, with the tube spinning, polish the outside.

    You can use the end where you have ground it down to a trough to get into the knot and loosen the strands. The trough is great for slipping along a strand and into the knot. Once loosened a larger marlinspike like the Myerchin Marlinspike can be used to great advantage.

    A splicing fid like this can save you a lot of rope.
    That's neat. A friend of mine is a knot knut and I bet he has gear I can borrow. "fid". My new vocab word for the day

    Grizz

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