Forums: Climbing Information: The Lab:
Spanish Burton conversion to 7:1 & other musings
RSS FeedRSS Feeds for The Lab

Premier Sponsor:

 


jktinst


Nov 20, 2011, 7:52 PM
Post #1 of 20 (7745 views)
Shortcut

Registered: Jun 29, 2010
Posts: 88

Spanish Burton conversion to 7:1 & other musings
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

EDITED TO ADD: BE SURE TO READ OTHER POSTS FURTHER DOWN FOR CAUTIONARY EXPLANATIONS ON THE USES OF THE SPANISH BURTON AND IT 7:1 CONVERSION

I’ve known about the Z pulley system and a few other self-rescue basics for some time but never went much beyond that. Recently I got into the Tyson & Loomis "Climbing Self-Rescue" and was quite taken with the Spanish Burton pulley system: same 3:1 ratio as the Z system, requires one more prusik but allows pulling down instead of up. I also liked the easy conversion of a Z 3:1 to a 5:1 but was disappointed to find no equivalent conversion option for the SB.

Of course there is the option to have a 2:1 pulling on the SB’s pull cord for a 6:1 system but that requires adding an upward pull anchor. If instead of the anchor, you attach the second pull cord to the primary prusik, you convert the SB to a 7:1 as shown here. Searching for this system on this website, elsewhere on the web and in various other self-rescue manuals, I keep finding either nothing (in most manuals), or references to a 7:1 system with no description (in many posts), or the description of a 7:1 based on a modified Z that, of course, requires pulling up. I should mention that, of Fasulo’s “Self-Rescue” book, which is one of the places where that description is given, I’ve only seen the pages shown on GoogleBooks. Anyway I figure that the SB-to-7:1 conversion is too obvious and simple not to have been described before so pointers to prior descriptions would be appreciated.

Working out the ratios also gives the proportions that go to the anchor and I became concerned with the forces that the SB and its 7:1 conversion apply to the anchor. In the “Mountaineering Handbook”, Connally dismisses concerns about high rates of transmission of load to anchor, but both he and Tyson&Loomis warn about ending up pulling hard on a high ratio system as a result of high friction and/or snags at the load end. Working out actual ratios using a 1:0.70 transmission factor over biners (ie in a self-rescue situation with no pulleys available), you get the following estimates of the ratios (along with the proportion transmitted to the anchor point in brackets).

- Z = 2.2:1 (1.2)
- Z redirected downward = 1.5:1 (2.5)
- Z conversion to 5:1 = 3.4 :1 (2.4)
- SB = 1.9:1 (2.9)
- SB conversion to 7:1 = 3.9 :1 (4.9)

After staring at these numbers for a bit, their obvious practical significance finally hit me. If you've got your feet planted on a ledge and are pulling up, the load on the anchor will be that needed to hold/raise the hanging load (weight of the fallen climber, plus any friction, snags, etc.) minus what you're applying by pulling on the system (eg Z system: anchor load 1.2 = hanging load 2.2 minus pulling load 1). Standing on the ledge pulling down, the load on the anchor will be the hanging load plus what you're applying pulling down on the system (eg SB converted to 7:1: anchor load 4.9 = 3.9 + 1). If you're on a hanging belay on the same anchor you're hauling from, whether you're pulling up or down and regardless of the system, the overall load on the anchor will be the same: your own weight plus the full hanging/dragging load. If you're pulling down, you apply more tension on the system but lighten your own weight and if you're pulling up, it's simply the opposite.

Based on this, it would seem that the choice of which system to use should be much more dependent on the specific situation than I've seen suggested anywhere. The SB is ideal for hanging belays. In that particular situation, it puts no more load on the anchor than the Z and is easier to operate, not just because of the movements involved but also because pulling down will ease the discomfort of sitting in the harness whereas pulling up would greatly increase it. One other advantage of the SB is that, if putting your whole weight on the pull cord by stepping into a foot loop is barely enough to raise the load, you can increase your own weight further (and somewhat decrease the hanging load at the same time) by pulling up on a handle (sling) clipped into the biner of the primary prusik. If that's still not enough, it's doubtful whether the Z converted to 5:1, with its less effective pull-up movement, would have been a very significant improvement whereas the straightforward conversion of the SB to 7:1 should definitely make a difference. Of course, it’s essential that the anchor be bomber and that care is taken not to end up pulling hard on this high ratio system because of serious snags or way too much friction.

In the opposite situation: belaying from a ledge (or even a half-decent stance) but from a not-so-bombproof anchor, it’s probably best to avoid the SB. Before deciding on hauling, all other rescue solutions should have been seriously looked at but, depending on how “not-so-bombproof” the anchor is, another hard look may be indicated. If hauling cannot be avoided and, despite your best efforts, you’re still not 100% sure of the bombproofness of the anchor, the go-to system should be the Z. However, converting it to higher ratios should be avoided as much as possible. In addition to masking the true load being applied to the anchor, these systems also make it too easy to generate spikes in the forces through acceleration if one is not careful to pull progressively. In this situation, in addition to making every effort to minimize friction and avoid snags, pulling up harder on a lower ratio system (adding a prusik on the rope at the tail end for better purchase) would be the way to go to raise the hanging load while further decreasing the overall load on the anchor.

In intermediate situations, it would be a matter of weighing all the factors, selecting the best possible combination of stance and pro options within the limited range of options handed to you by the circumstances, and installing the system that provides the highest possible safety (anchor loading, raising rate, etc.), as well as reasonable ease of handling, for that combination.

I’ve not seen a discussion of the choice of systems based on the circumstances in any of the manuals I've checked. I feel like I'm reinventing the wheel while being unable to find a description of the wheel anywhere. So, do these ramblings make any sense and could someone please point me in the direction of the bloody wheel?

(This post was edited by jktinst on Dec 10, 2011, 7:58 AM)


JimTitt


Nov 21, 2011, 10:16 AM
Post #2 of 20 (7676 views)
Shortcut

Registered: Aug 7, 2008
Posts: 978

Re: [jktinst] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

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.


antiqued


Nov 21, 2011, 1:53 PM
Post #3 of 20 (7636 views)
Shortcut

Registered: Aug 18, 2005
Posts: 243

Re: [jktinst] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

There's something else wrong with your 7-1 Spanish Burton - check the rope tensions again, or see Fig 2 in


jktinst


Nov 21, 2011, 3:26 PM
Post #4 of 20 (7610 views)
Shortcut

Registered: Jun 29, 2010
Posts: 88

Re: [antiqued] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

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)


Partner rgold


Nov 21, 2011, 3:44 PM
Post #5 of 20 (7600 views)
Shortcut

Registered: Dec 3, 2002
Posts: 1801

Re: [JimTitt] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

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.

True, but this does not mean there is an error in the "anchor loads," other than the fact that the term might be a misnomer. If L is one of the calculated anchor loads, that means the load on the anchor is L times the pulling force (and not, as Jim implies, L times the weight of the raised object). If you are raising a mass M with a A:1 system whose anchor load (as used in the diagrams) is L, in the absence of friction your pulling force is M/A and so the actual load on the anchor is (L/A)M. So, for example, the anchor load for the Spanish Burton 3:1 system is (4/3)M, which is less than the 2M upper limit Jim proposes.

The problem occurs when there is a lot of friction outside the pulley system, which is often the case; at the very least the rope will probably run over some edges. in this case the pulling force has to be raised and the anchor load goes up because of that. If there is only one rescuer, they presumably cannot pull with more than their own body weight, which would result in actual anchor loads the numbers in the diagram times the rescuers weight.

Even more problematic is high-friction situations in which multiple rescuers or perhaps even motorized winches are used to pull on the system. The pulling-force multiplying factors shown can then lead to very high anchor loads.


(This post was edited by rgold on Nov 21, 2011, 3:49 PM)


snoboy


Nov 21, 2011, 8:04 PM
Post #6 of 20 (7568 views)
Shortcut

Registered: Jul 19, 2004
Posts: 79

Re: [antiqued] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

antiqued wrote:
There's something else wrong with your 7-1 Spanish Burton - check the rope tensions again, or see Fig 2 in
In reply to:

I believe that the carabiner at the lower prusik is attached with a knot to the two ropes coming off it, not acting as a pulley/fool's tackle.


jktinst


Nov 21, 2011, 9:09 PM
Post #7 of 20 (7555 views)
Shortcut

Registered: Jun 29, 2010
Posts: 88

Re: [snoboy] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Ah. That does seem like a more likely interpretation of antiqued's comment. Sorry. In any case, snoboy's correct. The bottom biner is not a pulley, just the attachment point for 2 separate pull cords


JimTitt


Nov 22, 2011, 2:13 AM
Post #8 of 20 (7527 views)
Shortcut

Registered: Aug 7, 2008
Posts: 978

Re: [jktinst] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Well I got the answers to a lot of your questions the obvious way, since I was already set up for something similar I built a haul as in your third diagram (with the lower karabiner as a fixed point to get rid of the fools tackle bit) and put load cells on everything.

Since it is supposed to be a self-rescue set-up I used what most people would carry so a 12mm round bar HMS at the anchor and normal karabiners for the rest. 10.2 climbing rope and 8mm cord for the rest.

Practically the stretch and knot tightening was initially a pain but had the virtue of taking most of the jerkiness out (I can see this in the computer traces). Standing in a foot loop and pulling upwards at the same time was not the easiest thing in the world and I resorted to hanging in my harness, pulling upwards hard leads then to flipping over but you can pull a bit at least but it´s more sort of hand-over hand down the rope in reality!
And it is deathly work, one seemed to struggle like hell up and down fighting with Prusiks and foot loops to obtain about an inch of upward movement on the load and to get any substantial haul distance you need to jumar back up the rope every time!


The overall efficiency is the pits as one would expect with so many bends. 90kg load needed 37.3 kg to raise so 2.41:1 and the anchor load was then 129.1kg. There is a slight discrepancy in the sum of the load and pull of 1.8kg but this is the weight of the load cell and its shackles on the pull side).

To represent a stuck load I used an anchor bolt and hung myself on the pull side and pulled as hard as was feasible (perhaps one could pull better but as explained above this wasn´t as easy as one would think, effectively you can only use one arm).
The maximum load I could lift was 273kg and the max anchor load was 383kg, since I weight 90.2kg this morning it appears I pulled about 20kg which seems about right considering the awkwardness. And this increased the expected load I could raise (90,2kg X 2.41:1 = 217.4kg) by 55.6kg. Which obviously is more or less correct because to get 55.6kg on the load I´d need to pull 23kg (55.6/2.41 = 23).

Glad I don´t need to rescue people!


jktinst


Nov 22, 2011, 9:57 AM
Post #9 of 20 (7489 views)
Shortcut

Registered: Jun 29, 2010
Posts: 88

Re: [JimTitt] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Self-rescue hauling from a hanging belay (or better yet, hanging just enough to still be scraping and banging against the wall) is deathly work indeed no matter what system you use. Thankfully, it very rarely has to be done and more seldom still over long stretches of rope. But you never know when your partner might need you to haul him up by yourself. In these circumstances, « sorry mate, but hauling your ass would just be too bloody hard » isn’t really an option.

I see the loop-stepping + counterpulling as something that you would do if it helped raise a load at the limit of your 3:1 system’s capacity. It’s worth the hassle if it makes it possible to stick with the 3:1 and do the raise more quickly rather than have to switch to the 7:1 and take more than 2X longer for the same distance. I have not yet had the opportunity to set up the full SB and 7:1 system and try them out for real at my gym (the tests I did were at home, with smaller weights) and when I do, I will certainly not be able to record such good data so I really appreciate your willingness to give it a go and report back on such short notice.

Hopefully, using anodized biners that are not yet too scratched up thoughout the system would decrease somewhat the losses through friction because the numbers you are quoting are certainly quite discouraging (although they make a strong case for keeping at least one small nylon pulley on the rack for the longer, more remote climbs).

I have in the past practiced a hanging Z 3:1 redirected downward with loop-stepping + counterpulling so I wasn’t completely making things up when I suggested that. If I remember correctly I used one small pulley at the 1st position and the sequence was something like 1) step up into a crouch in the loop while balancing with one hand on the tail of the 3rd prusik (load did not move), 2) pull on the counterpull handle with the other hand to overcome inertia and 3) keep the load moving up by stretching into the step. I can well imagine that if you need to keep up the counterpull throughout just to complete the movement, it would be a lot harder.


JimTitt


Nov 22, 2011, 2:45 PM
Post #10 of 20 (7471 views)
Shortcut

Registered: Aug 7, 2008
Posts: 978

Re: [jktinst] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Don´t worry, the karabiners were by anyones standards in good condition, I don´t like screwing up cordage and rope over rough ones. The top HMS was brand new anyway and only used for rope testing. It is always a problem with testing generally to decide what to use, only testing with new gear doesn´t reflect what climbers normally carry so I mostly use good condition used gear.
I´ll run the test again in the morning with three brand new HMS´s but I doubt it will get much better. The best way to get the friction down a bit would be skinny dyneema slings and a pulley at the top but who´s going to carry one and more to the point how do you fit it into the belay when someone is already hanging on the rope?

Luckily all I´ve ever hauled in over 40 years climbing is my rucksack (and the odd beginner)!


Partner rgold


Nov 22, 2011, 6:36 PM
Post #11 of 20 (7446 views)
Shortcut

Registered: Dec 3, 2002
Posts: 1801

Re: [JimTitt] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (2 ratings)  
Can't Post

Jim makes a critical point I've been arguing for years, but he's put some numbers behind it.

Improvised hauling isn't going to be feasible in a significant number of cases.

People taking self-rescue courses may be mislead into thinking improvised hauiing is actually a practical self-rescue strategy. It isn't in many cases, and the time and fantastic amount of energy wasted trying to do it could easily have a critical negative effect on the outcome, since you are likely to end up with a victim who has barely budged and a rescuer who is totally exhausted and so much more likely to become a second victim.

If the victim in a climbing accident is incapable of helping themselves, then the party is in a bad way. Descending via tandem rappels is the most technically feasible option. If you are 20 feet from the top of a 1000 foot or more ciimb, then hauiing might be called for, except that the kind of injuries that totally incapacitate a climber are not especially compatible with dragging them up the rock.

If descending isn't appropriate, I'd say that 9 times out of 10, the best thing the healthy team member can do is call for help if that is possible, and if not, make the injured person as comfortable and insulated as possible and (rope) solo up for help. Wasting time, essential energy, and precious daylight trying an improvised haul is a very bad bet in these circumstances.

And 7:1 with all the prussiks, slings, and biners to arrange so that nothing bumps into anything else and then you manage, with every heave, to move the victim a few inches at best? Fuhgettaboutit.


knudenoggin


Nov 24, 2011, 10:10 PM
Post #12 of 20 (7344 views)
Shortcut

Registered: May 6, 2004
Posts: 594

Re: [rgold] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

rgold wrote:
Jim makes a critical point I've been arguing for years, but he's put some numbers behind it.

Improvised hauling isn't going to be feasible in a significant number of cases.

People taking self-rescue courses may be mislead into thinking improvised hauiing is actually a practical self-rescue strategy. It isn't in many cases, and the time and fantastic amount of energy wasted trying to do it could easily have a critical negative effect on the outcome, since you are likely to end up with a victim who has barely budged and a rescuer who is totally exhausted and so much more likely to become a second victim.
...
And 7:1 with all the prussiks, slings, and biners to arrange so that nothing bumps into anything else and then you manage, with every heave, to move the victim a few inches at best? Fuhgettaboutit.

Amen!

And typically that "7:1" (or whatever) is just a math-simple
theoretical MA, with the actual advantage being WAY less.
One can find the grossest nonsense in knots books, among others.
It can be quite eye-openingly instructive to actually try such
a system, with real weights --to see what considerable hauling
force does NOT move ... !

*kN*


binrat


Nov 25, 2011, 6:30 PM
Post #13 of 20 (7289 views)
Shortcut

Registered: Jul 27, 2006
Posts: 1155

Re: [knudenoggin] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

knudenoggin wrote:
Amen!

And typically that "7:1" (or whatever) is just a math-simple
theoretical MA, with the actual advantage being WAY less.
One can find the grossest nonsense in knots books, among others.
It can be quite eye-openingly instructive to actually try such
a system, with real weights --to see what considerable hauling
force does NOT move ... !

*kN*
What you mean that fancy setup won't work?? Personally 3 / 5 / 9:1 are simple to rig when tired using resources available to you. Try a simple 5:1, doesn't work flip to a compound 9:1 should and takes only seconds to convert to.


JimTitt


Nov 26, 2011, 4:30 AM
Post #14 of 20 (7265 views)
Shortcut

Registered: Aug 7, 2008
Posts: 978

Re: [binrat] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

One thing I noticed was that using Prusiks the amount of take-up on them after each lift was about the same as I´d lifted, with a 9:1 there must be virtually no height gain unless you are going miles down the rope on each haul. I changed over to an ascender for the 7:1 for this reason.
And by the time I´d got all this working my buddy would have been dead from suspension trauma or old age but admittedly it´s not the sort of thing I practice a lot, we tend to favour helicopters around here!


sherpa79


Nov 26, 2011, 5:18 AM
Post #15 of 20 (7258 views)
Shortcut

Registered: Dec 15, 2004
Posts: 108

Re: [jktinst] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

My opinion, unqualified though it may be, is that if you are in a small party rescue scenario, if you can't do it with a counter balance, you probably shouldn't be doing it.
3:1's have their place especially in a diminishing loop if you can rig that to your patient, even compounding a 2:1 (4:1) if your anchor situation will support that but anything with a greater mechanical advantage, whether you have the gear to support it or not, should be avoided.

Haul systems are cool and useful, but I find insofar as small party rescue goes there is an inverse relationship between the mechanical advantage of a haul system and prudence of using it in a given scenario.


jktinst


Dec 8, 2011, 10:19 AM
Post #16 of 20 (6995 views)
Shortcut

Registered: Jun 29, 2010
Posts: 88

Re: [rgold] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

I finally tested these systems and will have a whole lot to say about that shortly but, in the meantime, I thought I'd address a couple of points I left unanswered.

Regarding rgold's criticism of pulley systems in general: writing or teaching about these systems is not the same as recommending their use as a cure-all for rescue situations. The manuals are pretty clear that hauling an injured climber single-handedly is a last resort option ranging from very hard to just plain impossible. In case of serious mishap, trying to enlist the help of nearby parties (with their extra ropes and gear, as well as their manpower and expertise), should be high on the list of priorities but if you're in a solitary and remote location it's a different kettle of fish. The hauling you may need to do in self-rescue situations will often be over relatively short distances. If you want to leave your incapacitated partner safe and comfortable while you go get help and it is not possible to transfer him to a suitable anchor/belay spot either right where he is dangling or lower down, a short haul may well be your best option (and possibly the only one).

The actual ratio of 2.4:1 given by Jim for the 7:1 system, would mean that the per-biner efficiency was only 50.5% if the only inefficiency of the system was biner friction. Connally quotes 66%, Tyson&Loomis 70% (both specifically in the context of hauling systems) and Jim (in another thread and context) 1.53:1, ie 65.4%. These higher numbers probably correspond to a simple efficiency measurement for 1 biner + static cord whereas a hauling system probably also loses efficiency due to the stretch and contraction of prusik cords, dynamic rope, etc. Still, it may be more realisitic in calculations to appy a per-biner efficiency of 50% since more biners will typically mean more prusiks and more rope involved.


JimTitt


Dec 9, 2011, 10:37 AM
Post #17 of 20 (6949 views)
Shortcut

Registered: Aug 7, 2008
Posts: 978

Re: [jktinst] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Don´t worry too much about the various efficiencies quoted, a lot depends on the gear you are using and even more on what you test. The friction of nylon depends on a lot of variables and speed is one of the more important ones, in slow moving systems the coefficient goes way up and hauling certainly is on the slow side!
Another problem is when a rope makes a Z bend the efficiency is worse than two seperate bends the same way, the internal threads move to cope with the first bend and don´t come back fully when the rope straightens out so a reverse bend takes proportionally more effort.
Whatever one does it´s still pretty grim, Personally I´d be looking for a system where the hauler was a counter-balance and using leg-power on a simple 2:1 or 3:1 since this is where we are all much stronger.


jktinst


Dec 10, 2011, 8:03 AM
Post #18 of 20 (6903 views)
Shortcut

Registered: Jun 29, 2010
Posts: 88

Re: [JimTitt] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Sorry for another long post. Those who are not interested in self-rescue hauling systems should definitely not bother. For those who are, hopefully the large amount of information will be worth reading.

As I mentioned, I finally had a chance to try the systems in a more realistic practice. The gym was not an option (surprise) and since the climbing season ended some time ago around here, neither was a trip to the crags just for this. Instead I slung a rope up to a high tree branch in my backyard, prusiked up to it and set up the main hanging belay anchor and the regular Spanish Burton hauling system using the shortest possible prusik loops. I then tried to haul a partner 20% heavier than me... and got nowhere.

I tried to get the widest pulling length possible by using a fairly long cord, sliding the primary hauling prusik as far down the rope as I could (flipping just about upside-down in my harness), setting the pull-cord foot-loop as high as possible (ie right at the pulley biner) and stepping into it and pushing it down until I was again hanging in my harness with leg completely extended. The first couple of cycles just tightened the whole thing up but further cycles achieved no raising at all. My harness would stop me before I could take full advantage of the length of the pull-cord and it wasn't even clear whether the problem was related to the ratio or the pulling length. Switching to the 7:1 got me nowhere. To try and overcome the problem, I went back to the 3:1, lengthened my own cow's tail and the pull-cord so I would have a bit more freedom of movement. I tied a few step-up loops in the cord (using overhand knots on bights so they would slide OK through the biner of the pull-cord pulley point). Stepping up into the first loop from a hanging position lower down was quite acrobatic. A longer cord with more loops hanging lower down on my side would have helped but the cord wasn't long enough for that. In any case, this made it clear that the problem was not with the ratio. With this revised set-up, by the time I got to the end of my longer cow's tail again, I'd managed to raise the load a few inches but it would settle right back down by almost the same amount once I let the weight be taken up by the self-ratcheting prusik at the anchor pulley point (even after pulling the prusik as far down the rope as possible and snugging it prior to letting the weight settle onto it). Given the circumstances, going for yet greater pull distances (longer cow's tail, and much longer cord with lots of loops all along it) was not really an option (and probably would not have been realistic in many real rock situations. With daylight fading, I gave up on reverting to a Z system redirected for a downward pull.

I knew beforehand that pulling length was an important factor that combines with the mechanical advantage ratio to determine the efficiency and useability of a system (for a given MA ratio, the shorter the pulling length, the lower the ratio of the height raised by pulling to the height lost to settling) but I had not examined it closely in my initial analysis of the Spanish Burton and 7:1 conversion. I won't make that mistake again. With a single prusik pulling the rope, the Z can be pulled up until that prusik essentially reaches the anchor pulley point. By comparison, with an SB using the same anchor pulley point and the same initial position of the primary hauling prusik, the 2nd prusik that pulls the rope down allows the SB to be pulled only until the 1st prusik reaches just below the 2nd one, which is, at best, about one-half of the pull distance of the Z. I say "at best" because that assumes that you, as the puller, can actually move down along with the 2nd prusik, which is also your redirection point. If you are stuck at a fixed height with respect to the main anchor, either because of being in a hanging belay (as I was) or because of standing on a ledge with no easy way to step down from it - which are, after all, fairly likely scenarios -, the pulling lengths that you will be able to achieve with the SB will be shorter still. Of course, the situation would be even worse with the 7:1 conversion.

As a result of these tests and analysis, I now feel that the SB does not qualify as a downward-pulling alternative to the Z, which is how it is presented in the book. It is not nearly as user-friendly and broadly applicable as a Z redirected downwards. Obviously, Jim was able to make the 7:1 work, barely, in his testing facility so there are circumstances in which it and its parent system will work, but self-rescue hauling systems that only work some of the time, if the conditions and the room to manoeuvre are just right must be treated with a lot of skepticism. Having said that, the SB (and maybe even its 7:1 conversion) can have very specific applications that I'm still testing and will report on later.

After a quick evaluation of the pull distances of the other systems I’ve seen described, I’m getting a better appreciation for Sherpa79's comment not to bother with systems having ratios greater than 3:1, although I wouldn’t go quite that far. Without doing any further testing, it seems on paper that the conversion of the Z to the 5:1 halves the potential pull distance compared to the Z, unless you can pull from 2 or 3 m above (or behind) the anchor or set up a separate anchor for your redirect pulley/biner that far up (or away). This is doable in most horizontal, "crevasse rescue"-type situations but will be practical only in very few vertical "high up on a multipitch" ones. With the 5:1 set up with a redirect point level with the main anchor or standing on a ledge pulling up with no option to move higher in order to continue pulling, not only does each 1 m of rope that you pull translate into only 20 cm of raising but you have to stop pulling and reset the system when the primary haul prusik reaches approximately the half-way point between its starting position and the anchor. At least in this case, your redirection point does not keep moving down throughout the haul, like it does with the SB, but it still seems pretty limiting, especially if you do not have the option of moving the primary hauling prusik very far down the rope at each reset. Without running more tests or a much more detailed analysis, I can't tell just how "user unfriendly" or "only narrowly applicable" the 5:1 might be but it certainly would not be my first choice for a higher ratio system where my freedom of movement up above the anchor and down along the rope might be limited.

Using a 2:1 acting on a Z 3:1 for a 6:1 overall ratio would be even worse on both counts: greater pull-to-raise ratio and you have to stop raising at about one-third the height between starting point and anchor (again: unless you are able to keep moving up as you pull or to set up a secondary anchor and a redirect pulley for the 2:1 portion of the system much higher than the main anchor). The conversion of the Z to 7:1 that I mentioned earlier is more complex still to analyze, but, like the SB, it has a rope-pulling prusik on the other side of the anchor pulley point, so it seems fair to say that its pulling length efficiency will be "the pits". Basically, it looks like any system that requires adding lengths of cord or slings that contribute to the mechanical advantage (ie, any system that uses anything other than the rope, pulleys/biners and prusiks) will be fraught with complications and special considerations for vertical self-rescue. This means that pretty much the only option if a higher ratio is required is the Z 3:1 acting on a Z 3:1 for a 9:1 ratio. This system works essentially like the simple Z. It has no extra cord or sling and will let you keep pulling the rope until the primary haul prusik is most of the way up, stacked right under the secondary one. Of course with a 9:1 pull-to-raise ratio, that will take a fair bit of pulling but, at least, you should not get stuck in a situation where you are completely unable to overcome the settling of the load onto the anchor pulley point prusik because of pulling length limitations. Having said that, if you apply the 50% rate of transmission I discussed in the previous post because you have only biners and no pulleys, the 9:1 with a downward redirect works out to barely above 1.5:1. Sure makes a good case for parking some lightweight pulleys on the rack.

Based on all this, my latest acquisitions in the slow rebuilding of my trad rack are a lightweight prusik-minding SMC swivel-pulley, a spare round-stock anodized pear biner and 2 Petzl Ultralegere pulleys on ovals. The three biners don't have to be saved up just for an eventual hauling system, provided they are used in spots where they can be fairly easily recovered from when needed, so the only real additional weight is that of the 3 pulleys, which is quite minimal. For a simple Z, I would use the SMC for the anchor pulley point, the biner for the pulley point of the primary hauling prusik and the 1st Ultralegere for the redirection point. In terms of transmission efficiency in this system, interverting the first two units would be better but it's pretty essential to keep the prusik-minding pulley at the anchor pulley point. This set-up also keeps the Ultralegere close at hand near the anchor (as opposed to down by the primary hauling prusik), allowing me to make sure that the rope stays properly on that ridiculously light but fiddlier pulley. If I were to require a higher ratio (despite having rigged two prusik foot-loops or a prusik + garda hitch as a walk-up system on the redirected rope), I'll add another Z for a 9:1, with the second Ultralegere at the new redirection pulley point. Conservatively guesstimating a pulley transmission rate (incl. other linked inefficiencies) at 70%, these set-ups should give me effective ratios of 1.3:1 for the 3:1 and 2.4:1 for the 9:1; not great but it should be enough to cover a range of hauling needs and it's a lot better than the 0.9:1 and 1.5:1 you get with just biners.


jktinst


Dec 10, 2011, 8:14 AM
Post #19 of 20 (6899 views)
Shortcut

Registered: Jun 29, 2010
Posts: 88

Re: [jktinst] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

PS: in fairness to Tyson&Loomis, I should say that, aside from these issues with some of the hauling systems they describe, their book is excellent. In re-reading the section on hauling prior to posting the long post, I was also reminded that they do point out that the 70% transmission efficiency over a biner that they quote does not include many other inefficiencies inherent in hauling systems.


jktinst


Dec 17, 2011, 5:36 PM
Post #20 of 20 (6754 views)
Shortcut

Registered: Jun 29, 2010
Posts: 88

Re: [jktinst] Spanish Burton conversion to 7:1 & other musings [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

This thread is increasingly looking like a personal blog. Sorry about that. This post pretty much wraps up what I wanted to contribute to this topic.

Despite the issues with the SB that I discussed above, I could see that it has the advantage over the Z that you can set it up and start hauling right on a rope that's under tension (eg between an injured leader hanging at one end and the belay you just escaped from at the other). By comparison, the Z requires freeing up a fair bit of slack on the rope first. In the same vein, the SB does not have to be set up just below the anchor. As long as the climber's and the belay's sections of the rope are close enough together, it can be set up anywhere, eg just above the injured climber, which could be quite handy if you need to keep a close eye on him and may also help to avoid scraping him along the rock.

Of course, the system has to be set up in a way that provides a half-decent pulling length and that deals adequately with that pesky moving 2nd pulley/redirection point. I figured that this had to involve being on a self-belay on the belay's section of the rope.

I went back to the tree to try it out but didn't drag the partner out this time. I just filled up two large backpacks with every bottle, jug, pop can, etc. that I could. The combined weight was probably a bit lighter than me but not by much and I used only biners instead of pulleys so as not to make it too easy. I slung and tied off the anchor pulley biner high up in the tree (with the main rope already clipped in it and the self-ratcheting prusik already installed on the rope). I then set the primary haul prusik on the rope just above the backpacks and left it there as I prusiked myself up the free end of the rope taking the other end of the pull cord with me. Once the cord was pulled out just about as far as possible, I finished setting up the SB. For the 2nd pulley/redirection point, I used another round-stock anodized pear biner clipped into the same prusik that was linked to my harness for the self-belaying. At the end of the pull cord, I set up a foot loop on a garda hitch and used it to "hop" up the cord in long steps, hauling up the load at the same time as I, along with my side of the rope and my self-belay/redirection prusik headed back down. Once the two prusiks met and the cord was fully pulled down, I loosened the garda and prusiked myself back up to reset the system, etc. I didn't rig a two-foot walk-up system on the cord (prusik + garda hitch, as I mentioned in the previous long post). This would undoubtedly have been smoother and more efficient for hauling since there would have been fewer instances of settling the load on the self-ratcheting prusik but I wanted to keep one foot in my second self-belaying prussik, ready to climb back up the rope. Despite that inefficiency, the hauling went pretty well.

All this repeatedly prusiking myself up and hauling myself back down kept me plenty warm on a just-below-freezing day but could certainly be exhausting over long distances. It seems that this system would be most appropriate for short hauls. For example, it might allow you to bring an unconscious second more safely to the belay ledge. In the case of an injured leader you may be able to bring him to a safer/more comfortable resting spot somewhere between his hanging position and his last pro-turned-hauling anchor and do so much faster than if you had to prusik all the way back down to the bottom of the pitch to release the anchored rope and all the way back up to set up a Z hauling system. Having said that, the idea of encountering too much friction hauling with a regular SB, switching to the 7:1 and dividing the raising by 7 for the same mileage prusiking up & hauling down on the rope would be pretty daunting, even for a relatively short haul.

With this "tree and backpack" practice, there was no way to test how to keep the injured climber from scraping along the rock as I prusiked myself up and away from the load (while it was not moving) and then meet it half-way back down as I hauled it up. I can't imagine that it would be easy and, obviously, the lower the angle of the rock, the harder it would be, but there should be a much better chance of achieving this than if you were hanging or standing up by the anchor pulley point, pulling on a Z. Concern over how to manage the "no-scraping" technique for a given set of circumstances is going to influence how long a pull cord to use and how far up from your injured climber you are willing to prusik up before starting to haul.

None of this changes my opinion that the Z is a much more user-friendly and broadly-applicable system, but I'm glad to know that, if special circumstances require the use of the SB, I will know how to get it to work.


Forums : Climbing Information : The Lab

 


Search for (options)

Log In:

Username:
Password: Remember me:

Go Register
Go Lost Password?



Follow us on Twiter Become a Fan on Facebook