Forums: Climbing Information: The Lab: Re: [antiqued] Spanish Burton conversion to 7:1 & other musings: Edit Log




jktinst


Nov 21, 2011, 3:26 PM

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Registered: Jun 29, 2010
Posts: 88

Re: [antiqued] Spanish Burton conversion to 7:1 & other musings
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JimTitt wrote:
I think there is a slight error in your thinking, in all the systems you show with a downward pull you can never get a load on the anchor of more than the combined weight of the two people, either you go up or he goes up! What you do in the middle with purchases doesn´t make you any heavier.
The option to "increase your own weight" by pulling upwards on the load while stepping onto the pull cord of a Spanish Burton in a hanging belay was a figure of speech (probably not the best one to use in a post to The Lab). But that's what's great about this option: you're increasing the load you're applying to the pull cord beyond your own weight without changing the overall load on the anchor which will still be the combination of your weight and your partner’s being hauled up plus whatever drag or friction is applied on his end of the rope (the forces due to acceleration also come into play but I tried to keep things simple by assuming that the pull was gradual). Friction can add up to substantially more than just the sum of the two weights during each pull. Of course, friction works both ways. With the slight relaxation of letting the load get caught by the 1st pulley's prusik while you reset the system, friction will prevent your partner's full weight from coming to rest on the anchor but it will kick in again the seconds you restart pulling. Applying a high ratio system to serious snags can be disastrous. The overall load will quickly skyrocket until either you simply can’t pull anymore (if you’re lucky), your primary prusik starts giving out (if you’re a bit less lucky) or your anchor fails (if you’re not lucky at all).

antiqued wrote:
There's something else wrong with your 7-1 Spanish Burton - check the rope tensions again, or see Fig 2
If you’re talking about a similarity between the Spanish Burton, as described by Tyson&Loomis, and the Fool’s tackle shown in Fig.2, the attachment to the load in the SB is not through a pulley, unlike the Fool’s tackle. Imagining the 7:1 may have begun as a paper exercise but I have tested the SB and the 7:1. They work just fine and do indeed raise the load 1 ft for every 3 and 7 ft of cord pulled, respectively. Now what’s somewhat more interesting in your link is that what it calls the Spanish Burton is very different from that described by Tyson&Loomis, just to confuse things a little more.

(This post was edited by jktinst on Nov 21, 2011, 4:04 PM)



Edit Log:
Post edited by jktinst () on Nov 21, 2011, 4:04 PM


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