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  1. #11
    Senior Member bigbamaguy's Avatar
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    tjm:
    Thank you for the comments. I was looking at aluminum tubing at several suppliers on the net and all I can say is wow, that stuff gets expensive. Of course it was the same grade as an AR-15 receiver, but it was still almost $100 with shipping for an 8 foot stick.

    Also like the comments about the pad sleeve for the hammock. I am getting more into this with every response.
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  2. #12
    Senior Member TiredFeet's Avatar
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    Since you will be doing a DIY Bridge, play very close attention to the design of attaching the spreader bars to the suspension triangle.

    In designing the attachment design, do it such that the forces of the suspension triangle on the spreader bars is totally compression.

    The JRB Bridge is a good hammock, but the spreader bar attachment using the notches and rings introduces forces lateral to the spreader bar. Hence, the spreader bar become a weak point in the design.

    TeeDee has spent a LOT of time and experimentation in the design of the spreader bar attachment to eliminate lateral forces. He has finally accomplished his goal of eliminating the lateral forces. Any lateral forces on the spreader bar are now due solely to any bends in a spreader bar, i.e., bends in the bar before attaching as a spreader bar. Such bends, of course, divert the compression forces away from the axis of the bar and they become lateral forces which tend to make the bend larger.

    I know that TeeDee has pictures in his camera waiting to be developed when he returns and the roll of film is completed. So I will punt to his return a full explanation of his method of attaching the spreader bars. Quite a few things finally fell into place for the final design to work out.

    As far as the material for the spreader bars themselves, both TeeDee and I now favor bamboo. We have found it to be very light and strong. By heat treating the bamboo with a heat gun or propane torch, you can force the oils to the surface. The oil can then be spread with a rag to make a very nice smooth and water proof finish - you just have to be careful not to scorch the bamboo. You have to be very selective in getting the bamboo spreader bars to ensure that they are as straight as you can find. For the lengths needed that is usually not a problem. You can let the bamboo dry naturally or using the heat treatment above. Drying the bamboo will reduce the weight significantly. You will need to use the heat treatment to get the oils to rise though. The only part of using the bamboo spreader bars is the length. Our head end spreader bar is 32" to 33" which must be carried somehow. We have finagled a means of attaching the bars to our bamboo hiking staffs. This is no problem for us since the bamboo spreader bars and bamboo hiking staff combined is still lighter than out AL hiking pole.

    We have used both poplar and oak dowels for head and foot end spreader bars. Either is sufficiently strong enough. We used 5/8" for the head end and 1/2" for the foot end. This is probably the heaviest alternative we tried.

    We have used AL hiking poles with poplar or oak dowels - hiking pole on head end and dowel on foot end. That is both a strong and dual purpose solution. You will need to insert a dowel of the appropriate diameter inside the hiking pole so that when the pole is collapsed down against the dowel, it is the needed length. We couldn't find a hiking pole with an adjustable mechanism that was strong enough to hold against the compression forces. Thus, the need for the dowel inserted inside. If you use 2 hiking poles, then you automatically have 2 spreader bars. TeeDee and I both use one hiking pole and so we finagled a means of attaching the foot end dowel spreader bar to the hiking pole - out of the way until needed.

    We have stayed far away from specialized metal spreader bars due to weight. The only metal spreader bars that we almost tried are the tent poles available at Quest. The only trouble, if I remember correctly, is that the longer head end spreader needs needs a ferule connection which weakens the bar.

    Again, paying a LOT of attention to the method of attaching the spreader bars to the suspension triangle so that the attachment method does not introduce lateral forces, even very small lateral forces, will pay off big time in the end and so it is worthwhile to spend a lot of time in designing how you do it. Strive to have the attachment method introduce zero lateral forces. It can be done. It is easy to get lazy in this aspect of the design and figure you can always go back and change things. Not a good decision, since changing things is always harder than doing it right in the beginning.

  3. #13
    Senior Member TiredFeet's Avatar
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    Quote Originally Posted by gargoyle View Post
    I'd stay away from wood and bamboo. Growth patterns, wood density, knots, moisture content....to many variables.

    Personally, up the wall thickness of your alum. spreader bar and you should be good.
    Of course it will be heavier to pack.

    I sat in a bridge for a while and I weigh 330. Easton alum spreader bars.
    To be honest it wasn't all that comfy. And the narrowness seemed confining, hard to lay sideways in.
    Getting in and out seemed more difficult also.
    I can get plenty flat in my gathered ends. And sleep on my side.
    I'm not an expert on bamboo and can only speak for the patches within driving distance of home. But I have found bamboo to be strong and light weight. The variation from patch to patch is mostly in the diameter of the bamboo, from approximately 1/2" up to approximately 5" to 6". By carefully selecting the bamboo "tree" to cut, I can get a piece that is very straight and with a small taper from end to end for the length I need.

    The variation in strength across the patches I have access to is not noticeable if there really is any.

    Myself - personally think you are ruling out a material that has great advantages over a lot of other materials without actually having tried it.

    growth patterns in bamboo is mostly in the diameter and length of the segments.

    Density - maybe from state to state or coast to coast, but within a state, I would venture to guess that the density of bamboo is pretty consistent.

    knots - bamboo doesn't have any.

    moisture content - let it air dry or heat treat with a heat gun or propane torch. In about 30 minutes of heat treatment you will have a beautiful length of bamboo with the natural oils protecting it.

    Now for wood I would agree if you are talking about picking it up along the trail. But as far as going to Lowes or Home Depot and buying wood dowels, again, none of your arguments really apply.

  4. #14
    gargoyle's Avatar
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    I know bamboo has been used for thousands of years and major projects have been done with it. I'm not disputing the strength.
    Just in a heavy guy bridge hammock, are you willing to install it or suggest that another diy guy could do what you and TeeDee have done.

    Someone's personal safety is at stake here. My advice was to use something that has a more consistent strength. Mass produced alum. has better chance of performing well, that's all.

    I do have experience holding up 330 pounds. Have you tested bamboo with a heavy person?
    Ambulo tua ambulo.

  5. #15
    Jsaults's Avatar
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    As I said, I am not an engineer.

    But as the tube comes into compression loading, and as it bows a bit, doesn't one side of the tube receive additional compression while the opposite side is actually tensioned?

    Jim

  6. #16
    Senior Member TiredFeet's Avatar
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    Quote Originally Posted by gargoyle View Post
    I know bamboo has been used for thousands of years and major projects have been done with it. I'm not disputing the strength.
    Just in a heavy guy bridge hammock, are you willing to install it or suggest that another diy guy could do what you and TeeDee have done.
    I'm assuming that Jsaults is an intelligent person and can test the use of bamboo spreaders in such a manner that neither life not limb are in danger before deciding on using bamboo in the field.

    This is what all of the Bridge DIY people have been doing all along. All have tested their spreader bars and they have used materials as diverse as PVC piping to hiking poles to tent poles. I am sure that none of these people have simply installed the spreader bars and immediately taken a flying leap and landed in their Bridges.

    If he tests sensibly and finds that the bamboo works, then he has a very good, strong and light material that costs nothing except the effort to harvest and use.

    If he tests sensibly and the bamboo fails, then he can still use metal such as hiking poles or oak dowels.

    And yes it is entirely possible to test spreader bars in such a manner that even if they fail completely, neither he nor the hammock will suffer any damage whatsoever. I know this from extensive experimentation with some failed spreader bars in Bridge Hammocks. It is an experience guaranteed to boost the heart rate and make it difficult to extricate yourself from the Bridge Hammock, but no damage has ever been sustained by either the Bridge Hammock or the experimenter in all of our experiments. I have read of at least one (maybe 2) other people on the forums reporting on failed spreader bars and no damage was done or injuries sustained.

    Quote Originally Posted by gargoyle View Post
    Someone's personal safety is at stake here. My advice was to use something that has a more consistent strength. Mass produced alum. has better chance of performing well, that's all.
    I don't believe that advising somebody to use the costliest and heaviest material around without also advising that they may want to test under benign conditions other materials that have a possibility of working is the best way to go.

    Also, I don't believe that Jsaults personal safety is really at stake since I gave him the benefit of having the intelligence to test his DIY hammock under conditions that his personal safety is NOT at stake. This is only prudence, not only for the spreader bars, but for the design and construction of his DIY hammock. I do not assume that Jsaults will take his completed DIY hammock and immediately hang in a dangerous location where he could suffer injuries if any part of the hammock or suspension fails.

    If I am wrong in this assumption, would you or Jsaults please advise so that I can know to never make such an assumption for Jsaults in the future.

    Quote Originally Posted by gargoyle View Post
    I do have experience holding up 330 pounds. Have you tested bamboo with a heavy person?
    A heavy person - yes - we have tested on a variety of individuals, although we have never asked any of them their weight or asked them to step on the bathroom scales to determine it. Some people are very sensitive about their weight and we have always felt it better not to inquire, discretion was felt to be the better route. We have never had the bamboo fail, but I suppose there could always be a first time. Also, I believe that TeeDee's current design for attaching the spreader bars is partly the reason that we have never had the bamboo fail. His current design focuses the forces entirely on the axis of the spreader bar, no lateral forces and we have only used the bamboo on his current attachment design. I can see that for previous designs a failure of the bamboo could be possible if the load in the hammock was increased sufficiently since the previous designs did not eliminate lateral forces exerted by the attachment method. That could also have been true for oak dowels, hiking poles and other metal poles. If the attachment design introduces lateral forces on the spreader bars, then with sufficient load the lateral forces will cause the spreader bar to fail irregardless of the material used (assuming that the hammock fabric doesn't fail first ).
    Last edited by TiredFeet; 09-29-2010 at 19:45.

  7. #17
    Ramblinrev's Avatar
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    Really heavy hangers are probably not best suited to a bridge in my opinion. It has nothing to do with their weight. Rather it is more based on their girth. Bridge hammocks are very technical pieces of kit. The physics of the hammock are not restricted to the suspension lines. As you widen the width of the hammock to meet the added girth you extend the length of the spreader bars increasing the stresses on the bar. The feel of a bridge is sometimes mistaken for "shoulder squeeze" when actually it is a different feel of support of the torso. Widening out really makes the larger girth more difficult to accommodate.

    I found that sitting in my bridge was not very comfortable. A bridge really shines, from my perspective, in the flatness of the lie. I found the edge reinforcements cut into my legs even using the wider webbing. With my mobility issues the bridge is the only top loader I can get out of without outside assistance. In short, the bridge is a unique style which you will have very personal reactions to.
    I may be slow... But I sure am gimpy.

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  8. #18
    BillyBob58's Avatar
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    Quote Originally Posted by tjm View Post
    E

    Another question rattling around in my brain is the relative comfort for someone who is broad-shouldered.

    I use a BA insulated aircore pad [20"x72"] in the pad sleeve. To me, the pad significantly changes and improves the shape of the bridge from a round U to a flat l_l.

    I don't think I would like a bridge hammock that didn't have a pad sleeve with a pad in it. In fact, I am think of buying a wider pad to take more advantage of the 26" pad sleeve.
    I agree that a pad, and especially my 25" wide Thermarest Camprest, really opens the JRB Bridge up. I can lay on my back with my arms/shoulders by my side barely touching the sides, if at all. I am 6'1", 210 lbs, size 45 coat. Some day I hope to try it with a 26" wide CCF pad.

    Of course, if DIY, there is nothing keeping you from making the shoulder area a few inches wider, other than maybe more hassle with the spreader bar/tarp conflict.

    Still, I don't really have a shoulder "squeeze" problem with the JRB. My shoulder area- flat on my back- is forced into the "U" shape of the hammock, as though I am standing with slightly bad posture. It is not optimum for shoulder comfort, but not really (for me) a "squeeze" like I get with a too tight gathered end. At least not unless I try to have my arms down by my side, and I never sleep that way anyway. Plus, if I turn just a very few degrees towards side sleep position, the lack of shoulder room is not nearly as noticeable. And lastly, I have more shoulder room if I am farther towards the head end, with my head or shoulders on the end cap. Seems to me anyway. And then instead of a good pillow I need more of a neck pillow.

    Or, just put a pad in or make it a bit wider. The JRB Bridge works so well with a pad, compared to all non-bridge hammocks, that some day I am actually going to leave the quilts behind and try just a pad. But I have not quite had the nerve yet!
    For I consider that the sufferings of this present time are not worthy to be compared with the glory that is to be revealed to us....that the creation itself also will be set free from its slavery to corruption into the freedom of the glory of the children of God. For we know that the whole creation groans and suffers the pains of childbirth together until now.
    Romans 8:18,21-22

  9. #19
    Senior Member RePete's Avatar
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    Seems to me that if the first limiting factor is the spreader bars then my first thought is this. Replace the 2 piece spreader bar with a 1 piece spreader bar. I dont think wall thickness is the issue with JRB's spreader bars. It is the connection of the 2 bars. What ever material you chose for spreader bars I think the key is in using a 1 piece bar to support heavy weights.

    As for the comfort of sitting in a bridge hammock I dont think it is fair to compare it with a gathered end hammock. Some do find the bridge ok to sit in. I dont dispute that but I think even those people would be more comfortable sitting in a gathered end hammock. They are 2 completely different animals.
    Pete.
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  10. #20
    Senior Member dblhmmck's Avatar
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    The feel of a bridge is sometimes mistaken for "shoulder squeeze" when actually it is a different feel of support of the torso. Widening out really makes the larger girth more difficult to accommodate.

    I found that sitting in my bridge was not very comfortable. A bridge really shines, from my perspective, in the flatness of the lie. I found the edge reinforcements cut into my legs even using the wider webbing.
    That's interesting, Rev.

    It seems to me each of the issues that you mention may be attributed to the depth of the bridge. It seems the current trend as shown in Grizz's videos, favors the shallower cut. It is way more comfortable in my experience. I believe a wider person would benefit very much from such an alteration.

    I agree that a pad, and especially my 25" wide Thermarest Camprest, really opens the JRB Bridge up. I can lay on my back with my arms/shoulders by my side barely touching the sides, if at all.
    And I agree with you BillyBob. With a wide pad like a Stephenson's DAM, I could totally avoid contact with the sides of a bridge hammock. The feeling is fully supportive, while being very buoyant. I love it that way.

    Seems to me that if the first limiting factor is the spreader bars then my first thought is this. Replace the 2 piece spreader bar with a 1 piece spreader bar. I dont think wall thickness is the issue with JRB's spreader bars. It is the connection of the 2 bars. What ever material you chose for spreader bars I think the key is in using a 1 piece bar to support heavy weights.
    I think you are right otter46544. It makes tiredfeet's suggestion of bamboo pretty attractive to me. I was in China (about 15 years ago) and saw a high-rise building being constructed. Workers used scaffolding of bamboo over 30 feet off the ground- impressively strong stuff.
    "Better living through Hammockry"

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