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Thread: JRB Bridge

  1. #1
    Dutch's Avatar
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    JRB Bridge

    I just got back from the MAHHA hangout. JRB had about 5 display hammocks with assorted tarps, quilts, and hammocks. There were 2 bridge hammocks there. The first thing I noticed was the spreader bars were hollow bars that I think were 7/8 inch and separated in 3 pieces (the final version will have 2 sections I think). Their standard under quilts looks like they were made for it. The tree of the one bridge was a little further apart and that one they put attached the straps about 7 or 8 feet high on the tree. I meant to ask why but there were other question that was more pressing. The other bridge had the straps at the normal height. The amount of sag did not look like it affects the flatness of the occupant. I wish I had a tape measure, but maybe one of the Jacks will chime in when they get home. The spreader bars somewhere between 30” and 36” long. The cat cut was only 4 inches deep. They had nice rings on all 4 corners and 2 more were the support webbing meets 2 pieces of webbing that go to the corners. I think it looked like a perfect triangle with all 3 sides the same. The rings looked like mini SMD rings about 1” in diameter. The bug netting had omni tape that went all the way around and could be removed. It had end caps and it was made of 1.9 ripstop. It used ¾” webbing everywhere. It weighed 2 pounds 3 ounces without a tarp and cost $225.

    Now for the important part, it laid fantastic. I didn’t lay in for real long but I didn’t think the shoulder squeeze was very noticeable. Of course it was flat. The end cap really served well because if you slid back 6 inches it made a nice pillow and if you slid back 18 inches you could sit up and read like being in a recliner. I know we are all partial to our own tastes in hammocks but if you get the chance, try this hammock.

    I wanna send a real big Kudos to the Jacks for their displays. They had really taken time to set up various displays with cue card showing what kind of hammock, tarp, and UQ with the temp rating and the weights. They are also great to talk to and will help with anything. Others are fine, but Jacks R Better.
    Last edited by Dutch; 10-07-2007 at 07:44.
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  2. #2
    Senior Member schrochem's Avatar
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    Thanks for the report Dutch, I was wondering....
    I recalled some different details they said here so I went back and looked. I think on their website it has more details as well. I think it was 1" spreader bar 32" wide in two pieces, they used 3/4" webbing on the hammock then to 1" on the suspension with 1" steel rings.

    I was wondering about three things. The first was how the sewing of the pocket took the stress. It's perpendicular to all that stress and so I was worried it could be a source of failure. Second was something you mentioned about the lounger. That would be a great solution. Does it seem plenty strong enough? Is there a gap where your lower back is or does the hammock conform and support it? The last was about the notched rubber ends on the spreaders. What a great way to have them attach to the rings. Did that look like a pretty solid setup?
    Scott

    "Man is a stream whose source is hidden."
    RWE

  3. #3
    Dutch's Avatar
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    Quote Originally Posted by schrochem View Post
    Thanks for the report Dutch, I was wondering....
    I recalled some different details they said here so I went back and looked. I think on their website it has more details as well. I think it was 1" spreader bar 32" wide in two pieces, they used 3/4" webbing on the hammock then to 1" on the suspension with 1" steel rings.

    I was wondering about three things. The first was how the sewing of the pocket took the stress. It's perpendicular to all that stress and so I was worried it could be a source of failure. Second was something you mentioned about the lounger. That would be a great solution. Does it seem plenty strong enough? Is there a gap where your lower back is or does the hammock conform and support it? The last was about the notched rubber ends on the spreaders. What a great way to have them attach to the rings. Did that look like a pretty solid setup?
    I think when you say pocket you mean the small mesh pocket that would hold you headlamp small book. It is removable and attatches to the omnitape that holds the bug netting. It then has more omnitape on the outside of it so the bugnetting can still be attatched. It's genious because it isn't sewn in and cause stress and you can put it whereever you want. saying it could be used as a lounger may have been decieving. You can sit up to the point it is very nice to read a book. If you went all the way to where your but was where head should go it would become unstable. In any case there was no gap in my back and everythin is strong enough because it is the same construction on the endcaps as the side. The rubber notched ends were cool. One of the Jacks said the was something you can get a hardware store and just dip it in and let cure. I would wanna have some of that to redip because I think it would wear off or maybe metal would poke through. The set up is very solid. You don't have to tie anything out so you just click it on the tree and put in the spreader bars. The construction looks as good as anything I have seen. Main body is actually made of 3 peices sewn together so your weight is on their seams. They said the manufacturer made it like that because it was easier for them. It does add a possible failure place, but it seemed like it was very solid. I would think it would be easy to bend or kink the spreader bar if you were not careful. They would bend if you stepped on them. I bet the jacks would replace ones that got damaged. They are plenty strong enough holding the hammock apart. I still remember 3/4 inch strapping on everything except the main support the went around the tree, but maybe I am remembering wrong. Someone else should confirm soo enough.
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  4. #4
    Senior Member schrochem's Avatar
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    Thanks Dutch.
    I was actually talking about the main hammock pocket but it was cool to know how they did the small internal pocket. So what I was saying is the main pocket looks like its sewn in and that is where I was thinking it might be a problem. You said three pieces and I can't see the third. I see the main piece and the pocket sewn to the bottom. Am I missing something?
    Also interesting about the spreader ends. I found 5/8" of the 7075 to be plenty strong but I guess they need to make double sure in the production/reliability sense.
    Scott

    "Man is a stream whose source is hidden."
    RWE

  5. #5
    Dutch's Avatar
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    Quote Originally Posted by schrochem View Post
    Thanks Dutch.
    I was actually talking about the main hammock pocket but it was cool to know how they did the small internal pocket. So what I was saying is the main pocket looks like its sewn in and that is where I was thinking it might be a problem. You said three pieces and I can't see the third. I see the main piece and the pocket sewn to the bottom. Am I missing something?
    Also interesting about the spreader ends. I found 5/8" of the 7075 to be plenty strong but I guess they need to make double sure in the production/reliability sense.
    I did not check out the main pocket on the bottom because it had an UQ on. I wish I had. The main body is actually what is 3 pieces. There is a rectangle taht your body lays on. And then there is 2 side pieces that have a 4 inch catcut in them.


    I assume the pocket on the bottom was sewn at the same place as the middle piece. I am guessing it is difficult to cut the main body in one piece for the manufacturer. I am imagining they are die cut and not some old lady with a pair of scissors. But it is only a guess. They reassured me it is really solid stitching.
    Your spreader bars are Aluminium I assume. I thought thiers were rolled steel but I didn't check it out.
    Last edited by Dutch; 10-07-2007 at 12:41.
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  6. #6
    those seams look like they're running the wrong direction, forces in a bridge run side to side, those seams are strong end to end, much weaker side to side.

    a regular hammock is just the opposite, forces go end to end, and all seams run end to end (hh slit, eno seams) nobody uses a side to side seam in a regular hammock, putting an end to end one on a bridge is essentially the same thing. am i wrong here? seams don't ever handle stress well if the forces are running perpendicularly across it do they? seems like there will be problems particularly where forces are concentrated, like where you sit an read for example.

    every bridge hammock does have end to end seams where the fabric meets the webbing, but this is different because it's a curve, which spreads out the force over the whole seam where a straight seam does not.

    this is just my understanding of the concepts, i'm interested to see other's take on end to end seams in a bridge, or side to side seams on a regular style hammock.
    Last edited by warbonnetguy; 10-07-2007 at 11:08.

  7. #7
    GrizzlyAdams's Avatar
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    Quote Originally Posted by warbonnetguy View Post
    those seams look like they're running the wrong direction, forces in a bridge run side to side, those seams are strong end to end, much weaker side to side.

    a regular hammock is just the opposite, forces go end to end, and all seams run end to end (hh slit, eno seams) nobody uses a side to side seam in a regular hammock, putting an end to end one on a bridge is essentially the same thing. am i wrong here? seams don't ever handle stress well if the forces are running perpendicularly across it do they? seems like there will be problems particularly where forces are concentrated, like where you sit an read for example.

    every bridge hammock does have end to end seams where the fabric meets the webbing, but this is different because it's a curve, which spreads out the force over the whole seam where a straight seam does not.

    this is just my understanding of the concepts, i'm interested to see other's take on end to end seams in a bridge, or side to side seams on a regular style hammock.
    You're right about the direction of the forces. I wouldn't take that to mean though that no seam could withstand whatever forces there are, even focused ones when you sit or lean hard on it. Parachutes are sewn in panels, surely there are stresses and shocks that are oriented perpendicular to its seams...

    in any case, it seems like the JRB bridge is proof that longitudal seams in bridges hammocks can be done. It isn't evident though that any DIY bridge builder would need to, let alone want to.

    hey Dutch- thanks for the report. That's really interesting they're using a 4" deep suspension cut. I went 6" deep on my grey prototype lower lines, and didn't figure I'd risk any lower. Means you can get equivalent spread at the shoulders and fabric at the hips, using less fabric overall.

    Grizz

  8. #8
    Senior Member Walking Bear's Avatar
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    Seams

    Posted by warbonnetguy

    those seams look like they're running the wrong direction, forces in a bridge run side to side, those seams are strong end to end, much weaker side to side.
    I wanted to reduce the depth of the prototype bridge hammock, so I took out four inches by making a two inch fold in the bottom of the hammock. I stiched two rows of stiching to hold it. It looks fine with some testing and use of the hammock. The fabric if the 3 oz/yd out of the $1 bin.

  9. #9
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    I slept in one of the JRB bridge hammocks for about an hour and a half nap Saturday afternoon. It was great for any position except perfectly flat on your back or belly. All you had to do to lay on your back, was slightly lay to one side and the "shoulder squeeze" was gone. I do have broad shoulders and the spreader bars weren't as long as I have seen on some of the DIY pics here. Two people spent Saturday night in them, maybe we will hear from them.

  10. #10
    HappyCamper's Avatar
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    I slept in the JRB bridge all night on Saturday. Even though I like the simplicity of my A-sym, I get some knee pain in the A-sym that I didn't get in the bridge.

    I laid flat on my back in the bridge all night and I didn't have any shoulder issues. I'm a stomach sleeper at home, so I'm actually surpised that I liked it so much and was so comfortable. (I measure 17 inches from arm to arm across my shoulders.)

    Saturday afternoon I relaxed in the hammock for about an hour or more on my side and it was great too.

    I'm new to hammocks so I can't comment on any of the other questions. The Jacks are still out hiking, but I'm sure they will comment later in the week.

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