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  1. #21
    Ramblinrev's Avatar
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    Quote Originally Posted by dblhmmck View Post
    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 am the first to admit that I have not kept up with the refinements of the bridge. You are certainly correct that the depth and other adjustments could make a difference. Fundamentally, I think the two styles are more different than they are alike. As much as I liked my bridge, and I did like it a lot, as a big guy myself I found the gathered to be more comfortable and versatile for my personal use.
    I may be slow... But I sure am gimpy.

    "Bless you child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way."
    Mrs. Loftus to Huck Finn

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  2. #22
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    Really appreciate Tired Feet's comments, thank you.

    Set up my bridge & agree that the JRB triangle does add some lateral loading in the form of a bending moment at the ends. Too late at night for me to figure out how to reduce that or even eliminate that at the connection points.

    The longer the height (apex?) of the triangle the better since a suspension without triangle would be ideal as far as lateral loads but also seriously impractical since you would need four trees

    I think the connection of the two bars at the center strengthens the system since it is resistance to bending that we are trying to improve and the "doubled up" section is more resistant to bending than the single pole sections on either side of it

    I find it interesting how personal hammock comfort is. l think sitting up in a bridge either the end or using it as a camp chair with legs hanging out is one of its strengths.

    I think even those people who like gathered end hammocks would be more comfortable sitting and sleeping in a bridge hammock

  3. #23
    Jsaults's Avatar
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    tjm: A couple of thoughts......

    1. The longer triangle formed by the suspension lines, the less compression on the spreader bar. Makes perfect sense to me, even without an engineering analysis. And you really do not suffer a peanalty in terms of how far apart teh trees must be when compared to a gathered-end hammock, due to no "wasted" space in teh ends.

    2. I have never seen a bridge hammock spreader bar failure. Heck, I have never seen a bridge hammock except on this here inter-web! But I have seen MSR and Kelty tarp poles fail in high wind situations, and they appear to crumple at the terminus of the joint ferrule where there is a "stress riser". I assume that a spreader bar failure would take place at the same area.

    More assumptions on my part:
    I assume that the deeper and narower the bridge hammock, the less compression on the spreader bars. Conversely, the more one flattens the hammock body by lengthening the spreader bars, the more force exerted.

    I also assume that the wider & shallower the hammock, the more stress the fabric and webbing reinforcement must handle.

    So....much....information! And so far, this project is just an idea percolating in my brain!

    Jim

  4. #24
    Ramblinrev's Avatar
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    Grizz is probably the most experienced of the bridge "quants" as he has been doing research on this for literally years. He explored the relationship between the length of the triangle vs the benefits/risks and actually shortened his at one point but I don't entirely remember why. His reasoning and analysis is beyond my comprehension level. But it has been peer reviewed to the nth degree by the other quants on the forums. It' would be worth trying to find his analysis posts. Especially if you understand the language.
    I may be slow... But I sure am gimpy.

    "Bless you child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way."
    Mrs. Loftus to Huck Finn

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  5. #25
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    Filling your existing hollow spreaderbar with high density expanding foam should make it alot stiffer. It would be more lightweight than solid hardwood dovel inserts, and it would likely float as well.

    -Frikk

  6. #26
    BillyBob58's Avatar
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    Quote Originally Posted by otter46544 View Post
    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.
    As so often is the case, pros and cons. For me the major pro and con of bridge vs GE is lower body vs shoulders. For me anyway, the bridge is hands down superior for lower leg comfort, and for lumbar spine comfort while side sleeping. Unless I take some steps to deal with lower body comfort in the GE, and the bridge may still be better even then. IMO anyway. BUT, I think the gathered end hammocks def have the edge when it comes to getting my shoulders all set, back or side. I suspect that for me, there is a greater dif in lower body comfort than in shoulder comfort. But it will vary for other folks.

    As for sitting, I actually find the BMBH superior once again. Now admittedly, there is some leg discomfort where the very stiff edge cuts into my legs. ( things are reversed- now leg discomfort with the bridge! ) But I can usually shift around to minimize this, and I just put my pillow (or pad) between my legs and the hammock edge. Then I am left with back support similar to a recliner or good chair. In addition, I can get in the bridge and scoot way up towards the spreaders and into a corner. No leg pressure, and again just like a good chair or recliner.

    Most of my GE hammocks do not cause any leg discomfort when sitting. But other than that, the bridge is for me more comfy over all as a chair. But I MUST do something to deal with the leg pressure!
    Last edited by BillyBob58; 09-30-2010 at 22:25.
    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

  7. #27
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    Ramblinrev makes a very valid point Grizz has been making these and testing them in the real world. I bought a JRB BMB and am dusting of my old college text books on STATICS. [***].

    I imagine there were practical considerations for shortening the triangle such as total weight of the suspension or too long a suspension meaning you have to hang from farther apart trees and connect higher in the tree, as opposed to stresses being increases by a larger triangle. I just can't see how a shorter suspension triangle improves any of the forces acting on the suspension but I have been blind and or wrong many times before.

    You need to do a little homework using this website.

    You can easily locate all posts by Grizz and/or all posts with the term bridge in them.

    Identify the ones with good design information, print them out OR copy/paste them to a document and start distilling all that knowledge into bullet points. Then post those bullets and ask for feedback.

    For example, I found a few posts that discuss the trade-offs involved when trying to build bridges with wider spreader bars.

    Good luck,
    TJM

    [***] Old engineering question:
    Professor asks three students to determine how long it will take to cook a turkey.
    First one lists assumptions, derives heat transfer equations, identifies constants, etc. and calculates a time
    Second one assembles an elaborate test rig, buys a turkey and cooks it, and determines a time
    Third one calls his mom and asks her for the answer
    Which one is the engineer?
    Last edited by tjm; 09-30-2010 at 08:25.

  8. #28
    BillyBob58's Avatar
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    Quote Originally Posted by BillyBob58 View Post
    ................

    As for sitting, I actually find the BMBH superior once again. ...............

    Most of my GE hammocks do not cause any leg discomfort when sitting. But other than that, the bridge is for me more comfy over all as a chair. But I MUST do something to deal with the leg pressure!
    Actually, one other factor could shift the decision: how are you sitting? If sitting with feet on the ground, maybe while cooking over an alky stove, I don't think the BMBH can compete with many GEs. But if kicked back reading a book, using the back support the BMBH supplies, it can be great.

    Is this a hijack? If so, sorry. I guess the subject is bridge vs heavy hangers.
    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. #29
    gargoyle's Avatar
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    My apologies..

    I did some research on the forum and I see one post where TeeDee uses bamboo as a spreader bar.
    Interesting info, and I'll gladly test some, if the chance arises.

    I, in no way, meant my comments to be viewed as a direct assault on anyone. Nor a direct assault on someones intelligence.

    I was simply asking "have you tested bamboo with a heavy person?"

    My apologies to the forum and to Tired Feet.
    Ambulo tua ambulo.

  10. #30
    GrizzlyAdams's Avatar
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    Hi guys, work is slaying me so can't say much except
    • All the originial compression analysis was TeeDee's. I re-explained it and applied it.
    • Key point he made from the beginning and I've followed through on is to center the compression force. The Questoutfitter poles I use, slipped into openings between two lines of cord (dig around in my gallery or watch GrizzBridge videos, you'll see) do this in one dimension. Mathematically there is more force at the edge of the pole deeper into the triangle than the edge closer to the hammock, in principle producing some tendency for the pole to bow in towards hammock in the plane of the hammock, but I have never seen that. I think that to perfectly center the force in all dimensions takes a specialized piece of metal. Will be interested to see what TeeDee invention TiredFeet is talking about and whether that centers the force in all dimensions.
    • I have modified JRB BMBH to better center the force on their poles by replacing their suspension system. See the "Ask Professor Hammock" video.
    • On my GrizzBridge I shortened the foot end spreader bar, which allows for a shorter suspension triangle for a given compression force. One of my tricks there is to shorten the foot but shorten the triangle a bit less than I would to maintain the same force...meaning there is less force on the bar...and I am able to use a much lighter spreader bar at the foot.


    TTFN, duty awaits.
    Last edited by GrizzlyAdams; 09-30-2010 at 12:45.
    Grizz
    (alias ProfessorHammock on youtube)

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