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  1. #1
    Senior Member SteelerNation's Avatar
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    Unhappy Grizz, TeeDee, Bridge Experts - Help!!!

    OK, could really use some advice from the smart folks.

    I built my first DIY Bridge Hammock using all of the helpful instructions and recommendations. My efforts can be seen here:

    http://www.hammockforums.net/forum/s...ad.php?t=40762

    However, my primary desire was to try to create a hammock where I could sleep on my stomach. As such, this one didn't work out so well. I built it with a 44" width on both the top and bottom ends, and initially used a 32" top spreader and an 23" foot spreader.

    That worked fine when I was laying on my back, but when I lay on my stomach, I was squeezed at the shoulders and it pushed my heels together painfully on the bottom. At that point, I decided to try to lengthen my spreader bars to see if I could spread the hammock out some and give me more shoulder/foot room.

    I knew that I was probably pushing the compression forces on the poles, but I tried the 32" bar at the bottom and a 40" pole at the top. I used triangles that were around 75% of the bar length on both sides; hoping that would mitigate the forces enough for it to work.

    Unfortunately. . . . . .it didn't (see attached pictures)

    I kind of figured that I was pushing the bar (so to speak) too far with the 40" bar, but really want this to work, so was willing to risk a wally-world pole. The pole immediately sheared in half, right at the end of where the dowel rod was inside the pole for support.

    I guess my question is - is there a magical ratio that I can't surpass with regard to the spreader pole/head width length? If I keep it back at around 75% and increase my head hammock width to 53" to regain the 75% ratio with a 40" pole, will that help my shoulder problem at all? I'm thinking that the primary issue is the steepness of the sides where my shoulders are. If I could make that shallower, maybe I could take some of the pressure off of them.

    Any advice would be seriously appreciated!!

    Thanks,

    SN
    Attached Images Attached Images
    Please visit my AmJustDuane YouTube channel

  2. #2
    GrizzlyAdams's Avatar
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    how much do you weigh?
    how broad are your shoulders...if you have a sport coat, e.g., what size is it?

    I wouldn't recommend the wallypole for this use in the best of circumstances. A prime example of you get what you pay for.

    I do recommend tent poles from questoutfitters.
    Depending on the answer to the "how much do you weigh" question, the 0.625" diameter, or the larger one up, 0.724" diameter.

    The 75% recommendation for suspension triangle comes from the experience of TeeDee and myself, both under 200 lbs. The more the weight the greater the compression, and correspondingly, to keep the same amount of compression on the spreader bars for a larger weight you need to increase the length of the suspension triangle. And increase it some more when the body is flatter at the head end due to less fabric. The same sort of force amplification as you know you get with the suspension line approaching the tree is at work here, with the angle of the fabric approaching the corner of the hammock. Given your weight I can cook up some numbers for comparison.
    Grizz
    (alias ProfessorHammock on youtube)

  3. #3
    Senior Member DemostiX's Avatar
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    Love to read engineering questions here. I guess there's no better subforum than for a bridge hammock-- young, grizzled, hyphenated, trademarked,or abbreviated.

    From the blue, in case not elsewhere tried for light and strong: Chro-moly frame tubes from crashed bicycles. Around 1", butted, light, high strength. Long enough for foot end. (May I always have to source one from a bike not in my own stable.)

  4. #4
    Senior Member hangnout's Avatar
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    Quote Originally Posted by DemostiX View Post
    Love to read engineering questions here. I guess there's no better subforum than for a bridge hammock-- young, grizzled, hyphenated, trademarked,or abbreviated.

    From the blue, in case not elsewhere tried for light and strong: Chro-moly frame tubes from crashed bicycles. Around 1", butted, light, high strength. Long enough for foot end. (May I always have to source one from a bike not in my own stable.)
    After translating that post I assume you are talking about using 4130 chromemoly tubing for spreader bars. It would work but still be heavy compared to the aluminum tent poles. BER has already used carbon fiber tubes for a wider spread than most bridge hammocks. Without doing the math I would make the triangle suspension sides 100% of spreader bar width or let Grizz do the math for the given weight. It is hard to get trekking poles in a direct line for compression so that could have contributed to the failure also.

  5. #5
    Senior Member DemostiX's Avatar
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    I have not done the research here to find out how much strength is wanted by those using bridges to meet structural requirements and tolerate ordinary accidental abuse.

    Yes, I'm referring to Columbus, Reynolds 531, True Temper and other tube sets of 115,000+ PSI strength, following 4130. The 9 tubes set for a bike can come in at well - under 2kg. For bikes, the limit in thinness of the tube wall was set in the market by cosmetics-spoiling denting, not failure from crumpling. Tube end "meat" is there in the butted tube for brazing or welding. Per my previous post, I wouldn't suggest sourcing these new, only getting them from wrecks.

    Obviously, other hi-tech materials, CF(reinforced epoxy), aluminum, titanium, and others are available. If there's no weight penalty of steel, its just another affectation to know you've recycled a super-hi strength steel tube from another sport. Whether from bicycles or golf clubs, or hang-gliders etc.

  6. #6
    Senior Member SteelerNation's Avatar
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    Quote Originally Posted by GrizzlyAdams View Post
    how much do you weigh?
    how broad are your shoulders...if you have a sport coat, e.g., what size is it?
    For my weight, figure 185 lbs to be conservative. My sport coat size is 42 Short.

    Quote Originally Posted by GrizzlyAdams View Post
    I wouldn't recommend the wallypole for this use in the best of circumstances. A prime example of you get what you pay for.
    Yeah, thought that I'd give it a try. If you saw the video, I drilled into the handgrip to secure some dowels, so thought that it would be strong enough. . .


    Quote Originally Posted by GrizzlyAdams View Post
    I do recommend tent poles from questoutfitters.
    Depending on the answer to the "how much do you weigh" question, the 0.625" diameter, or the larger one up, 0.724" diameter.

    The 75% recommendation for suspension triangle comes from the experience of TeeDee and myself, both under 200 lbs. The more the weight the greater the compression, and correspondingly, to keep the same amount of compression on the spreader bars for a larger weight you need to increase the length of the suspension triangle. And increase it some more when the body is flatter at the head end due to less fabric. The same sort of force amplification as you know you get with the suspension line approaching the tree is at work here, with the angle of the fabric approaching the corner of the hammock. Given your weight I can cook up some numbers for comparison.
    I would really appreciate that! I really, really want to like this hammock type and find a nice, flat belly lie, and I sure appreciate any other ideas that you might have!

    SN
    Please visit my AmJustDuane YouTube channel

  7. #7
    Senior Member SteelerNation's Avatar
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    Quote Originally Posted by hangnout View Post
    Without doing the math I would make the triangle suspension sides 100% of spreader bar width or let Grizz do the math for the given weight. It is hard to get trekking poles in a direct line for compression so that could have contributed to the failure also.
    Yeah, when the spreader was 75% of width and the triangle 75% of spreader, the poles seemed to take the forces pretty well (I spent the night in the hammock with no apparent effects), but I sure over-did it with the longer pole length.

    If I can get good stomach sleep, I'm sure that I can handle the couple of extra ounces a separate set of lightweight spreader poles

    Thanks,

    SN
    Please visit my AmJustDuane YouTube channel

  8. #8
    Senior Member SteelerNation's Avatar
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    Just a bump to see if anyone was still willing to help me with the calculations.

    Thanks again, all!

    SN
    Please visit my AmJustDuane YouTube channel

  9. #9

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    I am not going to do any calculations for you. I will point out that much of this development has been experimental. You tried cheap hiking poles. One broke. Next step is to use spreaders with known integrity, such as 5/8" hardwood dowels. Worry about weight after you have determined the column strength needed for your spreaders. If you must use hiking poles for experimenting, try Black Diamond brand. They are made for climbers, not department store customers. They are more expensive than hardwood dowels, however.

    P.S. Just noticed. You are a Steelers fan in Georgia. Does that mean you are a **** Yankee?
    Last edited by DavyRay; 10-28-2011 at 20:53. Reason: Just Noticed

  10. #10
    Senior Member SteelerNation's Avatar
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    Quote Originally Posted by DavyRay View Post
    P.S. Just noticed. You are a Steelers fan in Georgia. Does that mean you are a **** Yankee?
    I am - and wear it with pride
    Please visit my AmJustDuane YouTube channel

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