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.
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2. Form a loop in the free end, near the tree.
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3. Flop the loop over up towards the tree, and push up the strand beneath.
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4. Slip in a toggle and tighten up.
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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.
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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.)
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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.
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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.
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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
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