[i_a_coops]

https://fierroequip.com/en/portfolio/punky-s/

As far as I can tell the only way to get hold of these is to ship them from Argentina - does anyone know different/have one I could borrow for a few weeks?

Would also be interested in any knowledge people have about falling on skyhooks in general. The one I want to be able to fall on is in a shallow but positive pocket in very good quality limestone (2 fingers wide 1/4 pad deep), and I intend to tension it down and use a revolver biner to reduce the impact force.

(Secondary question: there are also small RP placements on either side of the pocket. I'm unsure whether it's better to equalise the RPs together on one rope and have the other rope on the hook, or to equalise all 3 together and have just one rope on the lot?)

Any thoughts on this gratefully received as I'm not exactly experienced with skyhooks! My plan is to take some test falls on my setup with a knotted ab rope as a backup, but I also want to minimise my chances of blowing the RP placements out.

[remus]

I think James Pearson has some, could be worth dropping him a message to see how he got hold of them. Could also ask to borrow one, but I've got a feeling he may have bought them specifically for echo wall which he's just off to try.

Ed: could be imagining it but I think Franco might have some too?

[spidermonkey09]

Elite posting there Remus. Simultaneously a helpful response as well as delicately trailing a potential future significant repeat. Magnificent work.

[Fiend]

Told you that remus reports sig reps before the ascentionist even knows they've done it! P.S. Is Franco trying Echo Wall too?

[Tony S]

Would also be interested in any knowledge people have about falling on skyhooks in general.

In general, try not to fall off.

The one I want to be able to fall on is in a shallow but positive pocket in very good quality limestone (2 fingers wide 1/4 pad deep)

What’s the angle of the wall?Does the pocket have a lip? How prominent? Where does the apex of the arch of the hook sit? both height above any support and distance from front of pocket?

They can snap but they’re surprisingly strong. Flexing off and rock failure usually a bigger issues.

If you think at least one piece will hold, the physics is better for one rope on the three pieces (correctly) equalised. If you need to spread the risk, split the gear between both ropes.

The specific choice of rope(s) will likely make more difference than your revolver setup. While I wouldn’t totally believe equivalence between manufacturer’s stated peak impact force, it’s probably the best guide.

Not totally convinced by test falls as they will damage marginal placements, especially on limestone.


Best to stick to my first sentence: get it wired; don’t fall off.

[Steve R]

Sorry no use on the skyhooks but on this:

https://fierroequip.com/en/portfolio/punky-s/
(Secondary question: there are also small RP placements on either side of the pocket. I'm unsure whether it's better to equalise the RPs together on one rope and have the other rope on the hook, or to equalise all 3 together and have just one rope on the lot?)

I'd have thought all 3 equalised and then one rope (stretchy as pos) would be the better option.  You've probably thought of this but ripper sling? and provided there's decent fall length to distance off ground margin, a light belayer could also be good?  Good luck with the route.

[Tony S]

You've probably thought of this but ripper sling?

I remember reading that, in empirical tests, only the longest ones in very precise circumstances actually reduced peak impact force.

[Tony S]

Could also ask to borrow one, but I've got a feeling he may have bought them specifically for echo wall which he's just off to try.

Conditions look rubbish; maybe it’s worth a call 

[Paul B]

If you need the hooks then go on the website, send them an email and you'll get a PayPal request to pay and they'll be with you a few weeks later.

https://fierroequip.com/en/portfolio/punky-s/

I agree with others that one (skinny?) rope with everything equalised (perhaps not snugged up tight?) is likely the lowest impact.

Like Tony, I also remember reading the same thing regarding Screamers.

[remus]

On screamers, I think you also get a lot of vibration as they tear apart which could unseat the hook.

[Paul B]

On screamers, I think you also get a lot of vibration as they tear apart which could unseat the hook.

Can someone tag in Johnny Brown and Dan_M?

[Johnny Brown]

Of climbing ones, I've only tested the Charlet Moser ones. The standard Yates one looks similar. I've also tested a fair few industrial ones - they form the basis of all fall arrest lanyards used at work, although most work on a slightly different principle (woven not stitched) and the target impact forces are higher. All this is on test rig. I'm not sure why Petzl stopped making them when they bought CM.

They work as advertised. Whether they deliver an advantage in a particular situation depends. Some good tests here which suggest they certainly can: https://www.blackdiamondequipment.com/en_GB/stories/experience-story-qc-lab-to-screamer-or-not-to-screamer/

Note, though, on all those BD tests the screamers all 'bottomed out', i.e deployed fully. In an industrial context that would be a fail - there must always be sufficient capacity - as you end up with a largely static sling of more than sufficient strength. When that happens your peak impact force tends to be the bounce after full extension of the screamer. So without seeing the force/ time graphs it's hard to say how much the advantage of the screamer is obscured by the bottoming out.

I would agree with their conclusion to start by choosing your ropes carefully. This is one reason I've been on Beal Icelines for the last 20 years. The flipside is obviously stretch, so not the choice where you might hit the ground on stretch.

Deployment is typically fairly smooth, like a very noisy fast zip. I would think the vibration interval is too short to unseat hooks other than on a very hard, smooth, flat placement, but I would expect it to hammer-drill them in in soft rock. As above, if the force gets too high they're likely to open up or snap.

If you want to test the scenario you'd be welcome to do it at Abracadabseil. We have all the bits inc load cells with fast sample rates.

[Bonjoy]

I'm intrigued to find out what is considered "very good quality limestone". From hours of breaking up bits of limestone looking for fossil trilobites I draw the conclusion that a smooth uncracked surface does not necessarily mean solid rock. I'm very wary of placements on certain crags or levels on crags as a consequence. There is a huge variance in limestone quality in the UK and it doesn't always mirror what is considered good quality for climbing. Reef derived limestones for instance, which tend to be the pockety ones in the the UK, can be impure (lower % CaO3) and full of recrystalised voids and bits of fossil organism. These break up easily and erratically, whereas homogenous unfossiliferous limestones can be purer, have fewer points of weakness, are much harder  to break and fracture in a fairly predictable simple way. 

[MischaHY]

I was testing around with falling on skyhooks in lime a while back. Was surprised by how well and consistently they held. Better in rounded dishes and tensioned well. I just used the BD ones and took up to around 6m falls. Seemed ok with normal half ropes. Depends on the rock obviously but this was pretty soft lime.

[Tony S]

They [screamers] work as advertised.

I think the fairest thing to conclude, from your results and previously published evidence, is that the evidence is equivocal.

They may reduce the peak impact force, they are unlikely to increase it.

See:
https://www.ukclimbing.com/forums/gear/do_screamers_work_or_not-457691

https://web.mit.edu/custer/www/rocking/rocking.html

I’m unable to find the original CAI report.

[Johnny Brown]

Perhaps advertised was the wrong word. What I meant was that (as advertised) they, very reliably, tear at the specified force without sudden spikes in loading. I should add this wasn't always the case with industrial shock absorbers. Whether they 'can effectively reduce peak loads by 3-4kN' (as advertised by Yates) is entirely situation dependent. Given that the industrial ones reliably and safely arrest 120kg 4m Fall factor 2s I likewise take claims that they do nothing as entirely situation dependent. It might be worth noting that Petzl's latest models do this by progressively ramping up the arrest force, solving the longstanding problem of light people receiving injurous decelerations - effectively these never bottom out in the same manner.

I find it very strange that all the above links only share peak figures, rather than force/time graphs which are far more illuminating. This suggests to me that they only had load cells reporting peak forces which, in my experience, is severely limiting when interpretating results. It's not unusual to find you are measuring properties of the test rig rather than the sample, for example.

Other tips would be Fig-8s not bowlines obvs, and a slick belay device. Not at all sure about:

use a revolver biner to reduce the impact force

Interesting - is there any research to back this up? I remember discussing this with DMM when they came out as the concern was the opposite (by introducing a more efficient pulley you get more rope stretch and movement increasing mechanical advantage, = < force on climber, > force on runner). They assured me that at loads above about 2kN the sides of the biner pinched the pulley sufficiently to lock the wheel, although I later discovered this was on-the-hoof bullshit. But I'd like to see some test results.

(In my experience modelling generally fails to match reality as there are too many ignored variables and ropes don't behave like normal springs.)

If you think at least one piece will hold, the physics is better for one rope on the three pieces (correctly) equalised. If you need to spread the risk, split the gear between both ropes.

Perhaps in theory - link? All the testing I've done and seen suggests that equalising anchors basically doesn't work unless done over long distances and tiny angles, effectively using the rope stretch. So personally I'd always go for thin ropes clipped separately.

[Paul B]

My experience of falling on rollers is you go absolutely miles! I'd had some on very long slings for in the roof at Kilnsey and had been a bit lazy when I needed an extended QD on one of the more vert routes (I forget which one, not on the S buttress though) and it seemed like I just fell for ever. Light me, light belayer, Simmond skinny pink single etc.

[i_a_coops]

Thanks everyone for the excellent responses so far 

What’s the angle of the wall?Does the pocket have a lip? How prominent? Where does the apex of the arch of the hook sit? both height above any support and distance from front of pocket?

Dead vertical, and there's a nice dish in the back of the pocket for the hook. The rock outside the pocket is very compact. It's Pembroke limestone, the kind where very thin, sharp crozzly bits are actually very hard to break, which makes me think that a good looking non-crozzly hook placement in an 'innie' pocket rather than on a protruding flake is probably borderline OK to fall on. A quick google didn't reveal the CaCO3 % however so will do more research.

To minimise the chances of chiselling off the edge of the pocket, I'm thinking some tape on the end of the hook seems like a good idea. There will be dead space between the rest of the pocket and the hook, I was thinking a wedge of wood cut to the right shape to fill the dead space between the rock and the hook could both spread the force over more rock and reduce the likelihood of the hook opening out? The worry about the hook opening out is why I'm interested in the Fierro!

The revolver biner - my thoughts were that reducing friction in the biner would allow all of the rope in the system to stretch more equally, rather than the bit of rope between me and the biner stretching more and the rope below that stretching less. Also the belayer would be lifted more and the time of the fall would also increase. I'd assumed (based on no calculations and no tests) that this would outweigh the increased distance fallen and the increased load on the gear once everything has come to rest. The more I think about it the more I want to test this!

I'm also curious what people's reasoning is for all the gear being on one rope is. I was also under the impression that truly equalising things was really hard. Maybe I could equalise everything with skinny dynamic rope? Another factor is that I have to place the RPs, then use the pocket to do the crux before placing the hook at knee height (If I fall off this move and the RPs blow, the gear below should keep me off the deck).

[i_a_coops]

I was testing around with falling on skyhooks in lime a while back. Was surprised by how well and consistently they held. Better in rounded dishes and tensioned well. I just used the BD ones and took up to around 6m falls. Seemed ok with normal half ropes. Depends on the rock obviously but this was pretty soft lime.

This is what I wanted to hear!  What hooks were you using? And did you notice them flexing at all? ie were they the same shape after you'd taken some whippers on them?

[i_a_coops]

My experience of falling on rollers is you go absolutely miles!

Mine too! It certainly feels like less force on the climber, I hadn't clocked that that could be true while also putting more force on the gear though.   

[MischaHY]

I was testing around with falling on skyhooks in lime a while back. Was surprised by how well and consistently they held. Better in rounded dishes and tensioned well. I just used the BD ones and took up to around 6m falls. Seemed ok with normal half ropes. Depends on the rock obviously but this was pretty soft lime.

This is what I wanted to hear!  What hooks were you using? And did you notice them flexing at all? ie were they the same shape after you'd taken some whippers on them?

There’s like 3 different ones from BD and I tested all of them. They didn’t bend or change shape. I weigh 80kg.
Most bomber in small pockets is the triangle shape one.

[Tony S]

Interesting discussion.

use a revolver biner to reduce the impact force

Interesting - is there any research to back this up? I remember discussing this with DMM when they came out as the concern was the opposite (by introducing a more efficient pulley you get more rope stretch and movement increasing mechanical advantage, = < force on climber, > force on runner).

Hmm. I'd like to see a few modelled scenarios. I think you/DMM were talking specifically about "mechanical advantage" (i.e. where the climber is both the weight and the one holding their weight). Here we're only talking about "efficiency", the climber is the weight but an independent body is holding that weight. I can not presently see how increased efficiency would cause a greater peak impact force on the anchor (I'm not saying it can't, just I'd have to think about it more.) I'd also probably like to change my position on this and say revolvers might actually help a decent amount provided the DMM 2kN hocus is incorrect, though using a thin rope and larger diameter biner is probably going to get a similar efficiency at a high load (especially if the 2kN thing is true).

In my experience modelling generally fails to match reality as there are too many ignored variables and ropes don't behave like normal springs.

My understanding is that ropes modelled as heavily damped springs is actually very accurate. I believe the issue is that, in the real world, the efficiency of the top runner is low, your lower runners are never perfectly aligned (and it's basically nails to model this), and belay devices slip (good!) and belayers don't stand perfectly under the first runner (bad!), etc..

If you think at least one piece will hold, the physics is better for one rope on the three pieces (correctly) equalised. If you need to spread the risk, split the gear between both ropes.

Perhaps in theory - link? All the testing I've done and seen suggests that equalising anchors basically doesn't work unless done over long distances and tiny angles, effectively using the rope stretch.

I only said the physics was better, I don't get my hands dirty with engineering. I'm not convinced that "equalising anchors basically doesn't work unless done over long distances and tiny angles" - what do you mean by this?

The premise was that you are likely to end up with a higher peak impact force (on "a" piece, or "a" cluster) if using two ropes because the two ropes will never come tight at the same time so will not equally distribute the force across all the pieces. There may also be issues of having an "effective" greater spring constant (as you have two ropes not perfectly splitting the force, but I really would need to think that through more), if true(!), this would also lead to a higher peak impact force.

[Hoseyb]

I was testing around with falling on skyhooks in lime a while back. Was surprised by how well and consistently they held. Better in rounded dishes and tensioned well. I just used the BD ones and took up to around 6m falls. Seemed ok with normal half ropes. Depends on the rock obviously but this was pretty soft lime.

This is what I wanted to hear!  What hooks were you using? And did you notice them flexing at all? ie were they the same shape after you'd taken some whippers on them?

There’s like 3 different ones from BD and I tested all of them. They didn’t bend or change shape. I weigh 80kg.
Most bomber in small pockets is the triangle shape one.

The triangle one is the talon, as in Caff's "Wall of Talons"

[Tony S]

I was thinking a wedge of wood cut to the right shape to fill the dead space between the rock and the hook could both spread the force over more rock and reduce the likelihood of the hook opening out?

If you accurately created the wooden block such that void was filled and the apex of the hook was over the lip of the pocket (or into the wall) and the geometry was such that the hook didn’t slip(!) and the wood/rock didn’t deform/break(!), effectively you would have no moment around the apex and the force would only be along the back plate of the hook which is 3/4mm of tempered steel - ie not gonna break. But see the (!)s.

[Paul B]

You could use some Sugru and some cling film to make a perfectly shaped bung!

[i_a_coops]

You could use some Sugru and some cling film to make a perfectly shaped bung!

 

[X]

Do we get a mention in the FA list when you climb this project?

[i_a_coops]

Do we get a mention in the FA list when you climb this project?

Your faith is touching! I've only just convinced myself that I actually want to do it instead of going and trying something easier/safer/with nice shiny bolts in it. Tying in on the sharp end feels a way off yet 

But also yes, I think if I wrote it up confusingly enough I could make it look like everyone on here seconded it to really confuse climbing-history.org 

[remus]

But also yes, I think if I wrote it up confusingly enough I could make it look like everyone on here seconded it to really confuse climbing-history.org 

  give me a heads up when you're close so I can book in a few weeks of Dev time to make the necessary tweaks to ch.

[Moo]

Last time I used sugru and clingfilm to make perfectly shaped bung I ended up in A&E.

[i_a_coops]

Ok re the revolver, I think it's back-of-envelope physics time.

I think the extra distance fallen doesn't definitely/obviously translate into extra force on the gear. The extra distance gone down by the climber is going to be pretty much the same as the extra distance that the belayer gets lifted (?), so if the climber and belayer are roughly the same weight there's actually NOT more gravitational potential energy to be dissipated(?).

But, the extra distance fallen I think does mean the fall lasts longer (does it? with absolutely zero friction in any of the carabiners and similar weight climber + belayer I think the climber would get to a constant speed and not stop until the belayer hit the first piece of gear, whereas with infinite friction the climber would stop quickly. I can't see a reason there'd be a turning point in the graph of friction against fall time?)

Also, with no friction between the rope and the top biner, the entire rope will stretch equally, meaning the rope stretches more (?) and therefore more of the energy goes into that rather than impacting the rock. With infinite friction, the only bit of rope that stretches is the bit of rope between the climber and the last piece of gear, which in essence means a higher fall factor which is definitely worse.

The only scenario I can think of where lower friction increases the force on the top piece is where the belayer is still stood on the ground and the climber is sitting on the rope, where the friction force is supporting some of the climber's weight and taking the same amount of weight off the belayer. However if the belayer is lifted off the ground in the fall then after the fall I think the top piece is still taking the total weight of the climber and the belayer once everything has come to rest regardless of the coefficient of friction in the top biner

  

[i_a_coops]

(Obviously this is physics rather than engineering, I wouldn't be completely shocked if the variability of the efficiency of the pulley at different loads and/or weird boinging somehow meant that the peak force was actually higher with a revolver. I just think the first order approximation suggests otherwise    )

[Fultonius]

There's some posts on supertopo about this, and someone made a spreadsheet model that demonstrates it - the general gist seemed to be for low force falls it reduced peak force, but for high force falls (assuming the pulley actually rotates, which is debatable) it increases the peak force due to the 2:1 pulley effect.

It's counter-intuitive, but because the pulley increases the load on the belayer, the total load goes up (load on anchor is climber + belayer).

I'd love to see those guys at HowNot2 do some testing on this. (being and engineer I want it proven in the dirty unpredictable real world...)

Reminds me that I had an idea for a sky hook that I've never got round to testing...

[X]

There's some posts on supertopo about this, and someone made a spreadsheet model that demonstrates it - the general gist seemed to be for low force falls it reduced peak force, but for high force falls (assuming the pulley actually rotates, which is debatable) it increases the peak force due to the 2:1 pulley effect.

I’m probably being blind but I’m not seeing where this (2:1) mechanical advantage is coming from in the case when the climber is not also the belayer.

EDIT:
I think, if my search found what you were referring to, your SuperTopo person was looking at the situation when the leader’s top runner is also the belayer’s belay (ie on a multipitch route). I think the person posting then forgets this when re-posting it on another thread.

http://www.supertopo.com/climbing/thread.php?topic_id=731822&msg=732669#msg732669

http://www.supertopo.com/climbers-forum/859036/Physics-question-DMM-Revolver

[X]

Ok re the revolver, I think it's back-of-envelope physics time.

I think your para 3 is accurate (e see also https://m.petzl.com/US/en/Sport/Fall-factor-and-impact-force---theory) but the other paras I’m largely unconvinced by.

I think the following is probably a better basis to start from: https://4sport.ua/_upl/2/1404/StandardEqn.pdf

[i_a_coops]

I think the '2:1' is correct if the belayer is fixed to the ground, then the climber puts X kN of force into the rope, the belayer experiences X kN of force through the rope, and the gear gets 2X kN.

If the belayer jumps into the catch it's a whole different 

[X]

Hmm. I’ve never heard Newton’s Third law expressed in this way before.

In any case, as we’ve discussed it’s not entirely clear what overall impact (pun intended) having a pulley of greater efficiency actually has due to the other implications.

[duncan]

I'm also curious what people's reasoning is for all the gear being on one rope is. I was also under the impression that truly equalising things was really hard.

I was also under this impression. 

Another consideration is that ropes do some weird things when a piece blows. The rope is stretched before the piece pulls which can reduce its elasticity and so can increase the impact force (?) on the next piece that comes under tension.

High speed film after a piece breaks show the rope snaking around. I’ve twice experience a rope unclipping from the piece below the one that pulled in this situation, possibly because of the way the rope behaved.

Because of this I would tend to choose two thin ropes on separate pieces rather than attempt to equalise unless I felt there was a strong case for a single rope.

[X]

I'm also curious what people's reasoning is for all the gear being on one rope is. I was also under the impression that truly equalising things was really hard.

I was also under this impression. 

I think you’re right that equalising it perfectly is impossible in practice but the contract is with splitting over two ropes and I don’t think it is clear cut which is superior due to the previously mentioned issues. I’d be interested to hear about JB’s tests.

...
Because of this I would tend to choose two thin ropes on separate pieces rather than attempt to equalise unless I felt there was a strong case for a single rope.

I think this is a misunderstanding. I (others?) simply meant have the entire equalised top cluster on one rope (a skinny half), next lower gear on another rope.

(EDIT: expanded quote to make it clearer)

[Paul B]

I certainly wasn't advocating for a single!

[cheque]

My experience of falling on rollers is you go absolutely miles!

  As a layman it doesn’t seem like such a big modification but when you think about it (and/ or start using them) you realise how different the properties of a pulley and the bar of a standard carabiner really are!

I used to climb with someone who had aspirations of being a climbing instructor. They created what they thought would be the perfect gear for rigging top ropes on sport routes. These things were quickdraw tapes with a normal locking D carabiner at one end and a locking Revolver at the other, the idea being that you put one on each bolt of the anchors (with the gates opposed of course, safety first) and had a foolproof and ultra smooth toprope system.

I only saw them in use once but it was quite something 

[Johnny Brown]

(Obviously this is physics rather than engineering, I wouldn't be completely shocked if the variability of the efficiency of the pulley at different loads and/or weird boinging somehow meant that the peak force was actually higher with a revolver. I just think the first order approximation suggests otherwise    )

I'm no physicist but my empirical experience from doing a lot of testing is that it might do either depending on the situation. You can also get an amazing amount of variation test-to-test, even on a professional rail-based drop rig with no apparently obvious variables, whereas youtube/ blogs almost always do one 'representative' test for each variable and then the world treats it as gospel. My old back-up device research below is a great illustration - look at the Shunt



I could arm wave as to why the Shunt shows such variability, but why bother. In a climbing context some of the variation is due to the way knots tighten - a big part of the energy absorption especially on small falls - but more significantly, I suspect, due to the fact you are often creating something akin to a double pendulum - i.e. a complex system that creates chaotic results. When I spoke to an experienced rigger close to Dan Osman he had similar thoughts on why the rope broke on what was, after all, a Factor 1 fall. And that's before you factor in behaviour like Duncan mentions.

That's not to say you can't sometimes get fairly consistent results in tests, but I would always urge caution when applying them to real scenarios which are almost always more complex.

So if you have a specific scenario, copy it as closely as you can and then test it repeatedly. It does get expensive with devices like screamers - the above graph had government funding...

[Johnny Brown]

I think you’re right that equalising it perfectly is impossible in practice but the contract is with splitting over two ropes and I don’t think it is clear cut which is superior due to the previously mentioned issues. I’d be interested to hear about JB’s tests.

I haven't tested the exact scenario. I have tested the efficacy of various ways of equalising anchors. With more than two anchors over short distances like a belay it's impossible - the shorter strand always takes the bulk of the load. Even with two anchors it's very hard to do effectively - make the two strands identical length and a slight change of the angle of the applied load negates the equalisation. Whereas you can do it by doing something similar to a lead fall on double ropes - i.e. long distance and small angle between the two connections, letting the rope stretch do the work of equalising.

[X]

Whereas you can do it by doing something similar to a lead fall on double ropes - i.e. long distance and small angle between the two connections, letting the rope stretch do the work of equalising.

I'm interested in what this setup does to peak impact force on the two pieces/clusters compared to the other setup. While, I appreciate from what you write that, essentially in the "equalised" setup often the peak impact force will be on only one runner, that Peak impact force may(?!) be lower for the hazy reasons I previously mentioned

[Steve R]

I think this is a misunderstanding. I (others?) simply meant have the entire equalised top cluster on one rope (a skinny half), next lower gear on another rope.

That's what I meant too.  (Obviously not achievable most of the time if onsighting.)  My rationale was simply that if* the load could be spread between the 3 pieces effectively, then one rope gives a longer deceleration window due to more stretch and, intuitively, a lower impact force.

On the equalising perfectly thing, I'd agree it's hard for >2 pieces to line things up well - use slack knots(!?)  For 2 pieces, can think of a couple of ways to equalise perfectly - thinking similar set up to how the sling on a totem cam auto equalises between the two sets of lobes.  Granted it seems hard to avoid a bit of a potential shock load if one piece fails with that sort of set up though.

*seems like a very big if from this discussion

[Johnny Brown]

essentially in the "equalised" setup often the peak impact force will be on only one runner

Yeah that's what I'd expect.

that Peak impact force may(?!) be lower for the hazy reasons

I can't see it myself, but note that the impact force on the climber might be higher on double ropes, but lower on the individual gear as better shared. I'd also expect the result of a piece blowing to be more predictable, because you haven't got a sudden change in the direction the force is applied.

On the other hand, if I wasn't confident in the top cluster holding, yes I'd want them all on one rope and the other rope on the next piece lower. But that does increase the load on the top cluster and increase the chance of it failing, so it depends on where the next piece is and how much room you've got to fall into...

thinking similar set up to how the sling on a totem cam auto equalises between the two sets of lobes.  Granted it seems hard to avoid a bit of a potential shock load if one piece fails with that sort of set up though.

Ah yeah I was thinking predominantly of static equalisation. On two a sliding X or similar works pretty well, unless one blows at which point I think one per rope would be preferable.

Perhaps we can get DMM to make a Pivot for 3 x 7mms?