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  1. #1
    Senior Member TeeDee's Avatar
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    Cord Bridge Hammock

    Just a short note before I go out again.

    After much thought and experimentation, I have made some Bridge Hammocks using 2.8 mm Spyderline on the arc cuts instead of the 1/2" wide polyester tubular webbing.

    Comparison.
    • 2.8 mm Spyderline: 0.072 oz/foot.
    • 1/2" polyester tubular webbing: 0.17 oz/ft


    The webbing is 2.4 times heavier than the Spyderline for an equivalent breaking strength. Some of the 3 mm to 4 mm dyneema lines could be used to gain much greater breaking strengths.

    A given length of the webbing occupies less volume than an equal length of the 2.8 mm Spyderline, but the Sypderline packs down to a smaller size because it folds back on itself better than the webbing.

    I can stuff my Bridge Hammock made with the 2.8 mm Spyderline into a stuff sack 6" long by 3" diameter. Pretty small. My Bridge Hammock made with the webbing packs a larger than that.

    The ratio of the dyneema lines to polyester webbing weights at greater breaking strengths would favor the dyneema line even more. For example, Samson 3 mm AS-78 has an average breaking strength of 2900 lbs and weighs 0.51 lbs/100' or 0.0816 lbs/ft. Compare that to the Strapworks 1" webbing rated at 3,500 lbs and weighs 0.39 oz/foot. A ratio of 4.78:1. A considerable weight savings. If even more strength was desired, the 5 mm AS-78 with a breaking strength of 5,400 lbs could be used. It weighs 0.16 oz/ft which gives a ratio of 2.44:1 with the Strapworks 1" polyester webbing, so the webbing is almost 2 1/2 times as heavy for less breaking strength.

    The volume ratio would greatly favor the Dyneema line also. The ratio of the 3 mm AS-78 volume to the Strapworks 1" polyester webbing (2 mm thickness) for equal lengths is 1.8:1, i.e., the volume of the webbing is almost twice that of the dyneema line. The webbing is very stiff and would not pack well, where the dyneema line is very flexible and would pack down very well. Or the 5 mm AS-78 could be used. The volume ration is 0.65:1 favoring the webbing. The dyneema would still pack down smaller due to the stiffness of the webbing.

    The Spyderline Bridge Hammock is 1.5 oz lighter than the equivalent Bridge Hammock using the webbing. Both hammocks use the identical fabric pattern and the finished sizes are identical. They use the same Spyderline suspension and 3/4" ID stainless steel rings in the suspension for accessories and spreader bars. In short, they are identical except for the Spyderline instead of the webbing.

    The are of course, advantages and disadvantages to using the Spyderline versus the webbing.

    • Disadvantages:
      • The fabric on the arc cut from the shoulder area to just above the feet any Bridge Hammock is under a LOT of stress as anybody who has used a Bridge Hammock can atest. The webbing on the arc cut serves as an anchor for zippers or Velcro. With the Spyderline, that anchor is gone. The Spyderline is too narrow to serve for sewing a zipper or Velcro to it. Sewing to the fabric is NOT advisable. Thus, any Bridge Hammock accessories that require the zipper or Velcro on the Arc cannot be used. This, of course, is not a problem for me since I don't use either.
      • The Spyderline is more uncomfortable on the back and under the thighs when sitting crosswise in the Bridge Hammock for lounging. It isn't terribly uncomfortable, just more so than the webbing. Understandable since the forces are concentrated across the 2.8 mm ( approx. 1/8") width of the Spyderline instead of the 1/2" of the webbing. I don't find it so bad that I cannot sit crosswise though. But some might.
    • Advantages:
      • less weight. Not lots of ounces, but even 1.5 oz helps when it doesn't detract elsewhere, as in my case.
      • Packs smaller. Again not a whole lot smaller, but noticably and measurably smaller.
      • The Spyderline is slightly less expensive than the webbing:
        • Spyderline, 75' mini-spool, $23.75, $0.32/foot
        • 1/2" polyester webbing from Sailrite: $0.35/foot

        Not enough to make a big difference. But there are more suppliers for the Spyderline than the webbing.
      • Also, if a higher rating on the arc cut load bearing material is desired without the weight penalty of stronger polyester webbing, 3.8 mm Spyderline or one of the 3 mm Dyneema lines like the Samson AS-78 or the Amsteel Blue will more than suffice for anybody. Many times lighter than any of the 1" polyester webbings available. There are more choices available using line rather than webbing.


    Otherwise the two Bridge Hammocks (Spyderline vs. webbing) are identical in my use. The draft stoppers are interchangable between the two and the use of the draft stoppers is identical. Underqilts are interchangable bewtten the two and the useir use is identical.

    The two Bridge Hammocks are totally identical in use and almost in appearance. A person has to look closely to see that the Spyderline cord is used instead of the webbing.

    No time for pictures and no time to run out for film or get it developed. Sorry. Hoepfully when I get back in a few months.

  2. #2
    GrizzlyAdams's Avatar
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    I've been working on a warm weather model of bridge hammock that is as light as I can make it. One of the design changes was exactly this---replacing the webbing with cord, for all the reasons TeeDee enumerates.

    Concerns I've had include
    * having enough fabric take the strain of the cord. To address this I folded the curve cut of the fabric over 3", and then folded the top edge (now folded itself) over 1.5". Then 3 lines of stitching along the bottom 0.5" inch, creating a channel that is made of a double layer of fabric, 0.25" deep.
    * abrasion of the cord in the channel. For this reason I used uncoated Vectran rather than spyderline, because the shell coating of the spyderline is abrasive. Warbonnetguy and I had some discussions about this by PM a couple of weeks ago. He suggested making the channel of sil to further reduce the risk of abrasion. I thought this was brilliant, and so is what I've done.
    * slippage of the hammock body towards the center, when occupied. To address this I've sewn short loops of 0.5" webbing at the ends of the channel, through which the cord is itself looped. So when the body of the hammock is pulled towards the center, the pull is countered by the loops (attached to the cord) pulling the other way.

    But I'm not done with the rest of the body yet (details and pictures to follow when I'm done, and the hammock has passed testing). What I haven't known is whether this will actually work. So I'm very happy to see this report of TeeDee's implying that it might.

    Well, at least his does...I'm being a bit more aggressive in weight reduction than he describes and it remains to see if my model stays together when I get in the first time. There will be crash pads below!


    Grizz
    Last edited by GrizzlyAdams; 03-07-2008 at 00:31. Reason: spelling, of course....

  3. #3
    Senior Member TeeDee's Avatar
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    Quote Originally Posted by GrizzlyAdams View Post
    I've been working on a warm weather model of bridge hammock that is as light as I can make it. One of the design changes was exactly this---replacing the webbing with cord, for all the reasons TeeDee enumerates.
    I wasn't primarily interested in weight reduction, but in opening my options. Also, one of my primary objectives is a four season hammock. I really don't want a hammock for just one or two seasons.

    Quote Originally Posted by GrizzlyAdams View Post
    Concerns I've had include
    * having enough fabric take the strain of the cord. To address this I folded the curve cut of the fabric over 3", and then folded the top edge (now folded itself) over 1.5". Then 3 lines of stitching along the bottom 0.5" inch, creating a channel that is made of a double layer of fabric, 0.25" deep.
    Yeah - I was concerned about that also, but finally found it to be a non-problem. After extended use I have as much confidence in the corded Bridge as in the webbed Bridge. After using both and carefully watching the seam lines on the arc cuts, I see more stress on the stitches for the webbing than for the cord. The stitches for the webbed arcs are pulling and in the high stress areas around the butt, the stitch holes show daylight. I have full confidence that they will hold since they have. Contrarily I see no daylight on the stitch holes for the corded arcs. The corded arc stitching is showing more holding power if the daylight is any indication after many, many hours of use, testing and bouncing around in the hammock. I think the stresses are actually distributed better across the stitches on the corded arcs than on the webbed arcs and the stitch holes are showing this.

    Quote Originally Posted by GrizzlyAdams View Post
    * abrasion of the cord in the channel. For this reason I used uncoated Vectran rather than spyderline, because the shell coating of the spyderline is abrasive. Warbonnetguy and I had some discussions about this by PM a couple of weeks ago. He suggested making the channel of sil to further reduce the risk of abrasion. I thought this was brilliant, and so is what I've done.
    That was another concern I had initially. I decided there was 2 ways of attacking the problem (and probably many others ):
    1. ameliorate abrasion - this method seems to be the method you have decided to use. In this method you use channels like the silnyl and coated line. This leads to others problems that you are now trying to anticipate such as sliding toward the middle and correct with the webbing and coated cord. I finally decided against this method since it limits my options in line that can be used and adds complexity in the construction. I will be very interested in your results with this method when I return.
    2. eliminate abrasion - this is the method I decided gave me the most options in cords - essentially any cord can be used, coated, sheathed, whatever. Options are wide open. Also, the construction methods are very simple and basic. Making the arc with the cords can be accomplished in about 15 minutes after you have done 1 or 2. It as simple as making the arcs with the webbing. I came back to K.I.S.S. and the construction became obvious and simple and fast and efficient. I retained my goal in opening my source of arc load carrying materials. Also, I don't need multiple layers of fabric, rather a single layer works very well. As long as there is a possibility of abrasion, it will eventually wear through no matter how many layers. Even for coated line.


    Quote Originally Posted by GrizzlyAdams View Post
    * slippage of the hammock body towards the center, when occupied. To address this I've sewn short loops of 0.5" webbing at the ends of the channel, through which the cord is itself looped. So when the body of the hammock is pulled towards the center, the pull is countered by the loops (attached to the cord) pulling the other way.
    Yes, this was a concern also, but as soon as I returned to K.I.S.S. and eliminated the abrasion the sliding was eliminated also and became a non-problem also, just as it is with the webbing. Again instead of trying to ameliorate the sliding by the use of added webbing (which negates some of the weight savings of the cord), just eliminate it as a possibility.

    Quote Originally Posted by GrizzlyAdams View Post
    But I'm not done with the rest of the body yet (details and pictures to follow when I'm done, and the hammock has passed testing). What I haven't known is whether this will actually work. So I'm very happy to see this report of TeeDee's implying that it might.

    Well, at least his does...I'm being a bit more aggressive in weight reduction than he describes and it remains to see if my model stays together when I get in the first time. There will be crash pads below!


    Grizz
    Well I'm happy to report that after many, many, many hours the corded arcs are working as well as, and maybe better than, the webbed arcs. As I wrote above, the corded arcs seem to be withstanding the stresses better than the webbed arcs, if the visual indication of the stitching holes are a valid measure, as I believe they are.

    It's great to hear of your endeavors and I am sure that they will prove productive. I look forward to reading of them when I return in some months.

  4. #4
    GrizzlyAdams's Avatar
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    yes, to keep the cord from moving in a channel you need a way of keeping the cord from moving w.r.t. the fabric. Steve Robbins (the Aussie bridge guy) talks about threading cord onto the fabric. Clearly not what you're doing if it takes only 15 minutes. I thought of a couple of ways I might try this, but in the end figured that if I could keep the ends of the hammock body from being pulled in under weight, then the cord won't be moving w.r.t. the fabric. My own application of the K.I.S.S. principle, if you like. I'll be interested in seeing what you do, when you share it. Interested also in seeing if my method works!

    TeeDee, on a different topic...in your absence there was a discussion about bridge hammocks and tarps, with the observation that the spreader bar width keeps one from bringing the sides in close on most tarps used with other hammocks. I don't recall ever seeing you describe what you are using tarp-wise, particularly as your treatise on your bridge hammock system indicates you spread out 41", wider certainly than me. ?

    Grizz
    Last edited by GrizzlyAdams; 03-07-2008 at 19:27.

  5. #5
    Senior Member TeeDee's Avatar
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    Quote Originally Posted by GrizzlyAdams View Post
    ...........
    TeeDee, on a different topic...in your absence there was a discussion about bridge hammocks and tarps, with the observation that the spreader bar width keeps one from bringing the sides in close on most tarps used with other hammocks. I don't recall ever seeing you describe what you are using tarp-wise, particularly as your treatise on your bridge hammock system indicates you spread out 41", wider certainly than me. ?

    Grizz
    Sorry gotta go - ride to the plane to the trail head somewhere is on the way. Short answer - reduce friction to a minimum (like with plastic against silnyl), and letting the spreader bar tip rub doesn't matter. The sun will ruin the tarp first. It's here - having fun

  6. #6
    Senior Member dblhmmck's Avatar
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    Thanks TeeDee for the thoughtful analysis.

    I have also used the spydeline as "corded arcs" for the bridge styled hammocks that I have made. However, I was stringing it through tubular webbing which did not give me a weight advantage over using webbing or spyderline individually. My reason for the use of both cord and webbing was for creating expansion openings at the shoulders where the spyderline was allowed to go outside of the tubular webbing. And at the foot section below the knees the webbing ended. This required loop connections at the foot end to reattach to the spyderline corded arcs. I did experience a sliding a the middle effect until I made the reattachment point extend past the hiking pole spreader bars. The farther reaching attachment points kept the hammock fully extended and centered, once the poles were inserted.

    I am also in the planning stage of another hammock. I thought I would use 1 1/2" grossgrain ribbon on this model to encase the spyderline. I plan to sew the cat curve hemmed fabric edge to the ribbon then fold it over and sew the ribbon together. I will abandon the shoulder expansion openings, solving the shoulder squeeze with appropriate width of fabric. BTW I have found a width of 48" of fabric and 31" spreader bar at the head end to be adequate for me.

    My previous hammocks were 1.1 nylon, but I am interested in trying a lightweight polyester fabric that I found at Walmart. I will figure out the exact weight of the fabric and post my results of the new hammock next week (hopefully).
    "Better living through Hammockry"

  7. #7
    Senior Member greggg3's Avatar
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    TeeDee, is it just me or are you sort of refraining from saying exactly how you're attaching the cord to the material? Patent pending???

  8. #8
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    never being one to resist a puzzle let me offer a guess as to the technique to eliminate the possibility of abrasion - don't try to leave a channel to thread the cord through after the fact but instead sew the cord into the channel making sure that the one line of stitches is very close to the cord - this will create a high friction connection between the cord and the fabric thus eliminating the possibility that the cord will move relative to the fabric - no movement means no abrasion - the technique is similar to that is used in upholstery where a fabric covered cord is used along the edge of the arm of a chair or the edge of a cushion.
    Last edited by jlb2012; 03-08-2008 at 05:21.

  9. #9
    Senior Member IndyDan's Avatar
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    Question Help ... I'm stuck and can't get out!

    I am doing some testing on using Seamstick C3 Spinnaker Tape from Sailrite. http://www.sailrite.com/spinnaker-ba...=2&category=20

    I am testing using two strips of C3 for a width of 1 and placing the cord inside, then sewing a hem/seam as close to the cord as possible. I finish by placing another stitch parallel to the cord.

    I want to see if the cord will slide with the tape acting as a holding agent/bond. Also by taping the seam and then sewing, it should make a stronger bond.

    Other considerations: sewing corner supports and variations of stitching length.

  10. #10
    GrizzlyAdams's Avatar
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    Quote Originally Posted by IndyDan View Post
    I am doing some testing on using Seamstick C3 Spinnaker Tape from Sailrite. http://www.sailrite.com/spinnaker-ba...=2&category=20

    I am testing using two strips of C3 for a width of 1 and placing the cord inside, then sewing a hem/seam as close to the cord as possible. I finish by placing another stitch parallel to the cord.

    I want to see if the cord will slide with the tape acting as a holding agent/bond. Also by taping the seam and then sewing, it should make a stronger bond.

    Other considerations: sewing corner supports and variations of stitching length.
    I didn't know about this stuff before. Looks really useful, thanks for the pointer. I'd be really interested in knowing how much it weighs (once out of its protective wrapping).

    thanks
    Grizz

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