OLDS-Overhead Lowering...

Discussion in 'Rigging and Roping' started by Tom Dunlap, Aug 29, 2010.

  1. monkeylove

    monkeylove Well-Known Member

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    Someone who used one might have a better answer (I just ordered mine). But as I recall it has to due with the angle of the rope you are holding. Lets call it 180 for the porty and 90-120 for the OLDS if rigged off the limb. The same would hold true if it was a pulley and you held the rope. Take a look here.

    http://www.ropebook.com/information/vector-forces/angular-vector-forces

    If I am wrong please correct me someone.

    Frank
     
  2. Oroboros

    Oroboros Well-Known Member

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    [ QUOTE ]
    [ QUOTE ]
    ...
    The BS up top doesn't cause the same doubling effect on the top anchor, so you're working load is effectively larger than if you were conmparing a block up top and LD down low.
    ...

    [/ QUOTE ]

    Can you explain the physics of that please?
    I just cant imagine how this would work, as theres still the same load in the rope on each side of the BS.
    In my opinion it doesnt matter whats at the anchor point (frictionless pulley, real pulley, cambium saver, whatever).

    [/ QUOTE ]

    There is not the same load on each side of the BS. 15 lbs of pull is adequate to hold a 600 lb load. Friction ratio of 40:1. So the load on the anchor would be 615 lbs. Compare this to a block with base friction device. The same 600 lb load would result in 1200 lbs at the block's tie in point.
     
  3. monkeylove

    monkeylove Well-Known Member

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    I was not even thinking about the fact that we were talking about a friction device Oro. My bad, I was trying to explain basic pulley math. I knew one of my elders would correct me, lol.

    Frank
     
  4. southsoundtree

    southsoundtree Well-Known Member

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    [ QUOTE ]
    [ QUOTE ]
    [ QUOTE ]
    ...
    The BS up top doesn't cause the same doubling effect on the top anchor, so you're working load is effectively larger than if you were conmparing a block up top and LD down low.
    ...

    [/ QUOTE ]

    Can you explain the physics of that please?
    I just cant imagine how this would work, as theres still the same load in the rope on each side of the BS.
    In my opinion it doesnt matter whats at the anchor point (frictionless pulley, real pulley, cambium saver, whatever).

    [/ QUOTE ]

    There is not the same load on each side of the BS. 15 lbs of pull is adequate to hold a 600 lb load. Friction ratio of 40:1. So the load on the anchor would be 615 lbs. Compare this to a block with base friction device. The same 600 lb load would result in 1200 lbs at the block's tie in point.

    [/ QUOTE ]


    Keep in mind that this is a static scenario. I use it this way sometimes, however I sometimes negative block with it. As there is little rope to stretch in the system as compared to a block and basal mounted Lowering Device. I use hard lay three strand with mine, for the most part. It has a lot of stretch. I've never used True Blue or Dynasorb/ polydyne, but would think that they might be good choices to couple with the BS.
     
  5. Tree Access

    Tree Access Member

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    [ QUOTE ]

    There is not the same load on each side of the BS. 15 lbs of pull is adequate to hold a 600 lb load. Friction ratio of 40:1. So the load on the anchor would be 615 lbs. Compare this to a block with base friction device. The same 600 lb load would result in 1200 lbs at the block's tie in point.

    [/ QUOTE ]

    My mistake, its obvious that there is not the same load on each side. But I still think the load on the anchor is the usual doubled one. It cant just dissappear in the friction device?!
     
  6. Tom Dunlap

    Tom Dunlap Longest registered member

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    Not all of the load is converted to friction but a large portion of it. At the moment I don't have time to explain this...busy day ahead. Pete Donzelli did some research comparing rigging blocks with more efficient/less friction bearings to show how this works.
     
  7. southsoundtree

    southsoundtree Well-Known Member

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    There is some stretch taking energy, plus friction within the rope fibers, in addition to the friction on the drum.



    Think about if you have a POW up top, and the load is tied off, 100 percent load on the POW sling. Now uncleat and resist the slide, you've added some hold back force which is added to the POW sling.

    The doubling is when you imagine that there is zero friction, so it take 100 pounds of hold-back force to maintain a stationary 100 pound load in the air.
     
  8. Pelorus

    Pelorus Well-Known Member

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    [ QUOTE ]
    The Belay Spool can be purchased directly from BMS Rescue or one of his vendors.

    [/ QUOTE ]

    It arrived last week! Looking forward to using it.
     
  9. joe

    joe Active Member

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    [ QUOTE ]
    [ QUOTE ]
    ...
    The BS up top doesn't cause the same doubling effect on the top anchor, so you're working load is effectively larger than if you were conmparing a block up top and LD down low.
    ...

    [/ QUOTE ]

    Can you explain the physics of that please?
    I just cant imagine how this would work, as theres still the same load in the rope on each side of the BS.
    In my opinion it doesnt matter whats at the anchor point (frictionless pulley, real pulley, cambium saver, whatever).

    [/ QUOTE ]

    Here's a an older discussion which should help someone to understand why friction is increased with a greater number of wraps on a device.

    http://www.treebuzz.com/forum/showflat.php?Number=265835

    An article by Brian Kane in the Journal of Arboriculture and Urban Forestry.

    http://joa.isa-arbor.com/request.asp?JournalID=1&ArticleID=2976&Type=2

    Joe
     
  10. monkeylove

    monkeylove Well-Known Member

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    Wow, I just got mine today. Very impressive for the size of it. I of course had to go hang a few hundred pounds from it and test the friction. It is almost magical how much friction it creates compared to a round tube. Must be something to do with the rope forming a square under pressure.

    I like it alot so far, can't wait to get it in a tree. Thanks for pointing there.

    Frank
     
  11. Tom Dunlap

    Tom Dunlap Longest registered member

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    Joe,

    Thanks for linking that info.

    The OLDS/BS is a magical tool as far as I'm concerned. Simple, inexpensive and strong. If a stiff rope is used for rigging it will push up onto the rounded corners of the tool which makes yarding the rope up so easy. Much easier than if a PW is hung up there. Having the cheek plates capture the rope makes it much safer than using a PW too.
     
  12. Tree Access

    Tree Access Member

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    Yes, thanks! Unfortunately I still dont understand why the load on the anchor is reduced.
    Maybe the best would be to just feel and measure it myself, so please can someone help me to get a BS to Austria/Europe? :)
     
  13. Oroboros

    Oroboros Well-Known Member

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    [ QUOTE ]
    Yes, thanks! Unfortunately I still dont understand why the load on the anchor is reduced.
    Maybe the best would be to just feel and measure it myself, so please can someone help me to get a BS to Austria/Europe? :)

    [/ QUOTE ]

    Here is the contact info for the maker.

    http://www.bmsrescue.com/contact.html
     
  14. Tree Access

    Tree Access Member

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    Thanks, the problem is they gave me a shipping quote of $150...
    I am still hoping for a raising demand so that Treestuff will carry it :)
     
  15. Tree Access

    Tree Access Member

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    At least I can believe the reduced force on the anchor now, as I came up with the example of the rope having so much friction in the OLDS that you can let go the "up rope" but the load is not moving. Really simple, sorry for me being slow in getting that.
    But I still dont understand it, is the answer in the Capstan Equation? I do not fully understand that as well, maybe I should not have asked for the physical but for the dummy explanation of whats going on... ;)
    Someone?
     
  16. Tree Access

    Tree Access Member

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    Another try: Puzzling with forces I always try to think of them as Vectors, as doing so helped me a lot for my understanding in the past.

    So I thought when the rope is circling around an object the Force/Vectors coming in circles too, equalizing each other somehow. Has it something to do with that?

    So as long as the object is solid enough not to get crushed by the forces going into it from all the directions of the circle the (in my head) "missing force" is there.
    It is a "potential crushing force" in the object (or at its surface?). Bullshit or a little light in the right direction?

    It seems I like to use terms sounding like Physics, without being so. :)
     
  17. evo

    evo Well-Known Member

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    Tree Access, Your over complicating it. We all know that in a traditional lowering system the load on the anchor is 2X if the load is not moving up or down.
    So take a branch and tie it so that when you cut it off it is tied to the branch above. You now have a single leg of rope tied off so it's holding the branch (load) suspended. In that configuration the anchor is seeing 1x the load.
    So by placing the lowerig device above the load (OLDs, Portawrap, stub with wraps) you have only a single leg supporting the load + the force that you need to hold it..

    Say the limb is 100 lbs, you tie it off to hang it. That's 100lbs on the rope. Now you place your olds above, and it takes 10lbs to hold that 100lbs the total force on the anchor is 110lbs. The friction is supplying the holding power. Blocks/pulleys have very low friction, and that's where the 2x effect on the anchor comes from. If you were just rigging the lowering line though a crotch some of the force is taken up with the friction of the rope running on the surface of the tree.

    You can feel this with Ddrt all the time. Ascend the tree with a pulley, then ascend with out any cambium saver, then take a full wrap with your climbing line and try to move up or down.
     
  18. Oroboros

    Oroboros Well-Known Member

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    OLDS - 600 lb log plus 15 lbs friction input force. = 615 lbs
    Traditional 600lb log x 2 legs over pulley to base friction device = 1200 lbs at TIP.

    In dynamic situations the same basic ratios apply. The system with no basal anchor will always experience lesser forces. Personally I don't need to know what these forces will be exactly. I work well within the capabilities of the system.
     
  19. Merle Nelson

    Merle Nelson Well-Known Member

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    Explained well, I knew it but didn't understand why. I'm a happier person now!!!
     
  20. RescueMan

    RescueMan Active Member

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    I haven't posted here for years, and getting too old for tree climbing. But I do have a few brand new BMS Belay Spools for sale. See my Craigslist ad.

    Like Tom, I discovered these some years ago, used them in my rope rescue trainings and often specified them for rescue teams which needed to gear up. I also wrote an article about the advantages of a simple belay device over the then-popular automatic (or "fool-proof") belay devices. See Is Fail-Safe Really Safe?

    So I was also dismayed when Carroll Bassett said he was going to stop producing them. I offered to buy half his production run if he would make some more, which he agreed to do, and ended up with a box full, some of which I had to ship back to Bassett when his orders started to pick back up (I like to think my article in Technical Rescue Magazine had something to do with that).

    I've got seven left, in the original factory packaging, and I think Jeff Van Dusen is buying two of them. That leaves five. Let me know if any of you guys would like one.

    Email me at aVERT@ponds-edge.net if you're interested.

    Edit (12/18): I've already received interest from more people than I have belay spools, but if you really want one, send me an email and I'll put you on the waiting list in case some don't follow through.

     
    Last edited: Dec 18, 2014

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