Rope slippage in belay plate

Hi, might anyone have a link to some numbers on the amount of slippage that occurs in high FF falls when a typical belay plate is used? Not really interested in calculations unless they have some validation; looking for some experimental evidence of when slipping starts to occur and when it will be 10cm, 50cm.... etc.

Thanks

David Coleywrote:

Hi, might anyone have a link to some numbers on the amount of slippage that occurs in high FF falls when a typical belay plate is used? Not really interested in calculations unless they have some validation; looking for some experimental evidence of when slipping starts to occur and when it will be 10cm, 50cm.... etc.

Thanks

There are no realistic values available because the range of belayer gripping values is almost infinite and the effectiveness of belay device/rope combinations is also wildly variable. We use standardised values so we can research comparatively but there's no implication that any belayer/device/rope combination will achieve any particular value.

How far the rope slips through the device depends on the braking force achieved and the length of the fall, the fall factor is irrelevant. It's a calculation of energy dissapation by the device and the belayers hand.

Thanks Jim, maybe a better way of stating what I'm after is this. Most climbers that have held hundreds of falls have only held small falls and have the impression that the rope either never slips or only a few cm. Trying to convince them that aggressive falls might overpower their grip kind of needs some evidence. So I'm on the hunt 

David Coleywrote:

Thanks Jim, maybe a better way of stating what I'm after is this. Most climbers that have held hundreds of falls have only held small falls and have the impression that the rope either never slips or only a few cm. Trying to convince them that aggressive falls might overpower their grip kind of needs some evidence. So I'm on the hunt 

Maybe this: https://rockclimbing.com/forum/Climbing_Information_C2/The_Lab_F69/Re%3A_%5Brocknice2%5D_Rope_slip_in_factor_2_fall_belay_P1591608/

There are other possible sources in this query: https://www.google.com/search?client=firefox-b-1-d&q=belay+plate+rope+slip+threshold

Years ago, rgold sent me a bunch of stuff related to belay devices and falls. That included videos of people catching falls on drop towers. It isn't that your grip fails, but it's almost impossible to hold your arm down when the rope is yanked suddenly. The rope gets pulled through an ATC until your hand hits the device. And the belayer gets airborne too. Even with similar weights for partners. 

Anyway, watching people getting yanked right to the belay device over and over, even knowing it will happen, is impressive. Maybe google drop tower belaying? Something like that?

Found it. Belaying starts at about 16 minutes. It includes rope pulled through devices, arms yanked, airborne belayers and all three. Munster hitches are in there too! There are other ones like this. 

https://m.youtube.com/watch?v=zu_K-TD9T2U

Best, Helen

Thanks guys. I've read most of the paper based stuff, and the thread is just theory. The Italian video is great through. About half a metre of slack. Conclusion, don't get your hand too close to the plate 

https://www.researchgate.net/profile/Lionel_Manin/publication/281802420_Rock_climbing_belay_device_analysis_experiments_and_modelling/links/5fce3edc92851c00f858ee33/Rock-climbing-belay-device-analysis-experiments-and-modelling.pdf

https://watermark.silverchair.com/1077_1.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAA_0wggP5BgkqhkiG9w0BBwagggPqMIID5gIBADCCA98GCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMyglHN2qQSOYapvNcAgEQgIIDsCYXpz2U4zf-f2bXX6w6pBw3SJBRT6fnitA3Ioy6cSAXitbZgtJzXNOULu0HtvRK7-ZseAF94nzB4pHiMOOITLjYVOoxzMQHauU_rmtzaww_eat7eXpoDg4VjahEUYQXsPNhAqAMV5GSLqWJQnaEXbi9nopR1gGgXPwYaNeSgt4m36p2Ppk-dDT3i7a08Fd5a2t5jQy77yjOW8aZmz7V8OQAH0utFqIOzCOrHdBwhoQF84SMGYorElfIg0Wi2eIXPqFw_QWU9zpITXPLJv1F9eX6Nb7tGFQMzxz4y1hGgT3NHeUchbzK68xZHl-OOG7kbTOAa9PryQV3HTgR3nztkpw7cVIpLtqJXDNH7EP3sg7j_v28pn7EzYuxtX8PKZT7D0_wpOKVTX1rU7JKlMcZwrn7biWifOyqlEoVEPdhsb7-3rYns9ehXWkkcrlIqxHhL7z3XgyCswTrWa3hWG8NJHB6BKcRlkaWU6irmgxuFi7sfiMfsrKRfi9ILzjbNbHHpIIH3Y4rFEqvgQauGI7VtE8f6F_o5-ntIRXV08agzmZe0SQYmV9j1LY_jYtnaxIbUku76BIddvsJBpUzgzx1rHiql3djjJ4UMQRrmolKAuq9Hc_q6s3wBLyP2ntKU7GfYmdqI1BshHeVpaLqsZdxXGh2frF99sFYTxxL-YtxHYjDi2zM7RAoCd_049CWSVSen11J--ECErZ2tUhPG1ZdcMDswGpeZplAfOcIYPaEGJlB8HK2hIQTpKD-XIjgsK9Osc_SrnDRBsqe2wxuYiri6KpfxHhjI49vr7kJV6pXq8PIJCtr2gHHAy7xVlGec8FxLg0reQzNqatGiBef_oEhrSOrIZN3-wBzZeg5IVSv131kG1CKj1-LXn8YQ_IFq26lr9iXTBJTI8eLu68UkViZiD-pXXwTRqlKHJzWldWTMubmfvePwOkr7m_riID8PHcWlUti286cnHfb7llcmV9Tj82gm0BNSVCYC1czuEEPo7p0Fq-Yu8nXB-EAJcfELA-uKVgismOzEqJTcRekxIhoIV1unVvSlesh3IS130B5o1GCNN8ey4GfynEGmrJ_i0WnxvdqhGAin2d5oM3XgN0FJUUt0eWLmaA1f6MbagyozXlUJVAFiJ9HZaIz8HGz1y0bxbpHf6it1rwzLB1P61TvCrnh6f_KS3Cvoq1YDq76cl83AmNrVlKVEkWI6jnk4kfUckyGgoGLzNQvREvrZqci2FnUme1FJSlBLnBf41F3FOm4

Old lady Hwrote:

Munster hitches are in there too! 

Best, Helen

Mmmm I love Italian cheese.

David Coleywrote:

Thanks guys. I've read most of the paper based stuff, and the thread is just theory. The Italian video is great through. About half a metre of slack. Conclusion, don't get your hand too close to the plate 

Conclusion, consider wearing gloves to belay. It isn't the rare FF2 to worry about. That's other worries than rope slippage, imo. But even single pitch lead falls, easily, if there's enough force.  Sometimes, even top rope falls. Not much friction, heavier climber...

Also fun, is the slow slippage when someone hangs half the day. "HEY!! The longer you hang there, the farther away that next bolt will be!!"

:-)

Philip Magistrowrote:

Mmmm I love Italian cheese.

Oops. Autoidiot strikes yet again.

Jim Tittwrote:

How far the rope slips through the device depends on the braking force achieved and the length of the fall, the fall factor is irrelevant.

Sorry to drift, but is the last part really true ?  Comparing a 3m fall with 3m out to a 3m fall with 10m out, it's hard to believe the 10m rope wouldn't absorb a larger fraction of the fall energy before the force reaches belay slippage levels (leaving less energy to be absorbed via slippage).

Serge Swrote:

Sorry to drift, but is the last part really true ?  Comparing a 3m fall with 3m out to a 3m fall with 10m out, it's hard to believe the 10m rope wouldn't absorb a larger fraction of the fall energy before the force reaches belay slippage levels (leaving less energy to be absorbed via slippage).

While it's true the rope does dissapate some of the energy by heat as the internal fibres move against each other the effect isn't dominant nor well researched. The more "dry" treatments that are applied the less the effect will be as well. We know reasonably well what the effect is through belay plates when rappelling but in just a straight fall it's not really studied. 

Rope stretch is anyway probably detrimental once the force is such that the rope slips through the device as it increases the time the the rope slips through the belayers hand. There are two criteria of when the system is a failure, one is when enough rope slips enough to injure the belayer and the other is when the injury causes the belayer to release the rope, due to reaction times the longer (in time) the rope slips the higher the probability the belayer lets go of the rope.  

David Coleywrote:

Thanks guys. I've read most of the paper based stuff, and the thread is just theory. The Italian video is great through. About half a metre of slack. Conclusion, don't get your hand too close to the plate 

It has to be theory, we can't do live testing where we deliberately expose the subjects to injury. But the theory is fairly accurate and matches anecdotal events quite well. Everyone from my generation knows why "live" belay drop tests such as at Plas y Brenin where dropped. Pit Schubert of the DAV was registered disabled after one such test and Munter (of Munter hitch fame) was badly injured demonstrating his stupid idea which is why he became a convert to the Italian hitch.

Jim Tittwrote:

 Everyone from my generation knows why "live" belay drop tests such as at Plas y Brenin where dropped. Pit Schubert of the DAV was registered disabled after one such test and Munter (of Munter hitch fame) was badly injured demonstrating his stupid idea which is why he became a convert to the Italian hitch.

Any chance you'd be willing to share these stories for those of us who don't know them?

Jim. Did you just say a munter hitch is not an Italian hitch? 

The Munter hitch as originally developed by Werner Munterwas actually a half hitch around the body and over the shoulder. Unfortunately at the demonstration to the UIAA it broke his collarbone, the odd rib or two and caused compression injuries to some internal organs. After Munter recovered he became a proponent of what is now called the Italian Hitch which had also been demonstrated at that time.

dave custerwrote:

https://www.researchgate.net/profile/Lionel_Manin/publication/281802420_Rock_climbing_belay_device_analysis_experiments_and_modelling/links/5fce3edc92851c00f858ee33/Rock-climbing-belay-device-analysis-experiments-and-modelling.pdf

https://watermark.silverchair.com/1077_1.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAA_0wggP5BgkqhkiG9w0BBwagggPqMIID5gIBADCCA98GCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMyglHN2qQSOYapvNcAgEQgIIDsCYXpz2U4zf-f2bXX6w6pBw3SJBRT6fnitA3Ioy6cSAXitbZgtJzXNOULu0HtvRK7-ZseAF94nzB4pHiMOOITLjYVOoxzMQHauU_rmtzaww_eat7eXpoDg4VjahEUYQXsPNhAqAMV5GSLqWJQnaEXbi9nopR1gGgXPwYaNeSgt4m36p2Ppk-dDT3i7a08Fd5a2t5jQy77yjOW8aZmz7V8OQAH0utFqIOzCOrHdBwhoQF84SMGYorElfIg0Wi2eIXPqFw_QWU9zpITXPLJv1F9eX6Nb7tGFQMzxz4y1hGgT3NHeUchbzK68xZHl-OOG7kbTOAa9PryQV3HTgR3nztkpw7cVIpLtqJXDNH7EP3sg7j_v28pn7EzYuxtX8PKZT7D0_wpOKVTX1rU7JKlMcZwrn7biWifOyqlEoVEPdhsb7-3rYns9ehXWkkcrlIqxHhL7z3XgyCswTrWa3hWG8NJHB6BKcRlkaWU6irmgxuFi7sfiMfsrKRfi9ILzjbNbHHpIIH3Y4rFEqvgQauGI7VtE8f6F_o5-ntIRXV08agzmZe0SQYmV9j1LY_jYtnaxIbUku76BIddvsJBpUzgzx1rHiql3djjJ4UMQRrmolKAuq9Hc_q6s3wBLyP2ntKU7GfYmdqI1BshHeVpaLqsZdxXGh2frF99sFYTxxL-YtxHYjDi2zM7RAoCd_049CWSVSen11J--ECErZ2tUhPG1ZdcMDswGpeZplAfOcIYPaEGJlB8HK2hIQTpKD-XIjgsK9Osc_SrnDRBsqe2wxuYiri6KpfxHhjI49vr7kJV6pXq8PIJCtr2gHHAy7xVlGec8FxLg0reQzNqatGiBef_oEhrSOrIZN3-wBzZeg5IVSv131kG1CKj1-LXn8YQ_IFq26lr9iXTBJTI8eLu68UkViZiD-pXXwTRqlKHJzWldWTMubmfvePwOkr7m_riID8PHcWlUti286cnHfb7llcmV9Tj82gm0BNSVCYC1czuEEPo7p0Fq-Yu8nXB-EAJcfELA-uKVgismOzEqJTcRekxIhoIV1unVvSlesh3IS130B5o1GCNN8ey4GfynEGmrJ_i0WnxvdqhGAin2d5oM3XgN0FJUUt0eWLmaA1f6MbagyozXlUJVAFiJ9HZaIz8HGz1y0bxbpHf6it1rwzLB1P61TvCrnh6f_KS3Cvoq1YDq76cl83AmNrVlKVEkWI6jnk4kfUckyGgoGLzNQvREvrZqci2FnUme1FJSlBLnBf41F3FOm4

I read the paper on research gate. Thanks.

There seems to be several problems with it to my, inexperienced, eye

1. they say in tests the max hand force is 160N. This seems 2 to 3 times too low based on Jim's work, and I can hold way more than 16kg tied to a rope. I'm 62kg and have a desk job.

2. their fake had applies 160N through the whole cycle. I have an untested belief that what can happen is that the rope does not always overpower the hand in this way, but rather the belayer holds the rope, the arm is overpowered, the hand therefore stays tight on the rope and slides up towards the plate. Hence the full theoretical resistance (in this case 160N) is not supplied by the belayer. I suspect that once the hand hits the plate they might grip hard, or let go!

3. The FF is given as 0.12 and the fall short. I have used those belay devices, and never found any slip at FF=0.12 and a short fall. Although their "belayer" can't move and I think the FF might be 0.2, but maybe I added it up wrong. They get over 1m of slip. This would burn I'm guessing, so I would have remembered.

Helen's video (from 21min) does clearly show that the hand moves up the rope, not the rope through the hand (or some combo or both).

Jim Tittwrote:

While it's true the rope does dissapate some of the energy by heat as the internal fibres move against each other the effect isn't dominant nor well researched. The more "dry" treatments that are applied the less the effect will be as well. We know reasonably well what the effect is through belay plates when rappelling but in just a straight fall it's not really studied. 

Rope stretch is anyway probably detrimental once the force is such that the rope slips through the device as it increases the time the the rope slips through the belayers hand. There are two criteria of when the system is a failure, one is when enough rope slips enough to injure the belayer and the other is when the injury causes the belayer to release the rope, due to reaction times the longer (in time) the rope slips the higher the probability the belayer lets go of the rope.  

I'm wondering if you guys are talking about slightly different things. At the risk of being shot down by the more knowledgable, is it not the case that the FF matters, in that, until the FF is great enough, the rope keeps the force at the plate below say 2.4kN and hence one's 300N of hand resistance means the rope does not slip. (Based on a plate multiplying the hand resistance by 8, as Jim's work suggests). Once over 2.4kN the rope slides and FF is not relevant, the key being mxgxh giving the energy that must be dissipated in the plate-hand (ouch) combo.

Conclusion, don't get your hand too close to the plate.

True; it's very painful.

Thanks for the Munter story.

Sounds kind of like a dulfersitz rappel, which I wouldn't wish on anybody.

WF WF51wrote:

Conclusion, don't get your hand too close to the plate.

True; it's very painful.

No, your hand can be all the way down by your hip and go until it's stuck in the ATC. Consider wearing gloves to belay. Been there, done that, including stuck in the ATC with feet off the ground. Fortunately, I merely had a piece of glove stuck in the ATC. I did see a belayer hanging from their hand. They kept the belay and managed. Not fun.

@David Coley, in one of these, there is one single person, a guy, who manages to not have his arm yanked to the plate or hitch. That's a lot of strength, plus, a lower arm locked off really fast, or locked to start with (knowing it was coming). I am certain I can't hold the amount of weight that would lift my weight off the ground, with one arm, nor would I have an arm tensioned all the time. Keeping my hand closed? Easy. As soon as a fall starts, I'm locking hands on rope, and the body is thinking mitigation, not locking up an arm that doesn't matter. Step back, squat down then be lifted, step in, or just go for the ride.

Best, Helen