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If (as BD research suggests) ice screws hold predominantly through their threads and not the "picket" effect - and the threads on ice screws all seem to be the same length, why bother buying longer ones?
I've thought about this several times - longer screws seem only to have a longer smoothe section above the thread and NOT more thread.
Maybe this is a thread too far or perhaps I'm just being thick and I'm missing something more obvious?!
I've thought about this several times - longer screws seem only to have a longer smoothe section above the thread and NOT more thread.
Maybe this is a thread too far or perhaps I'm just being thick and I'm missing something more obvious?!
In reply to Chris Reid: when they pull test them they find that there is extensive surface fracturing around the screw. The longer the screw therefore the more likely the threads are to be in good ice further in. This would be especially true if the the surface ice is sun damaged etc.
So in new, non aerated ice at say -5 in the shade, it probably doesn't matter. But on late season sun damaged ice, longer screws are more likely to get their threads into more dense ice further in.
So in new, non aerated ice at say -5 in the shade, it probably doesn't matter. But on late season sun damaged ice, longer screws are more likely to get their threads into more dense ice further in.
In reply to TobyA:
Having dealt with a fair amountof dinner plating ice it is (I assume) reasonably clear that this fracturing is indeed surface fracturing and not really to any depth and so employing a 16cm screw over a 22cm screw would make little difference- whad'ya reckon?
Just some idle thoughts!! (And with a mind to cost and weight saving)
Having dealt with a fair amountof dinner plating ice it is (I assume) reasonably clear that this fracturing is indeed surface fracturing and not really to any depth and so employing a 16cm screw over a 22cm screw would make little difference- whad'ya reckon?
Just some idle thoughts!! (And with a mind to cost and weight saving)
In reply to TobyA:
Anyway, with regard to the aerated ice theory - you can always clear that down to some denser, healthier ice surely?
Anyway, with regard to the aerated ice theory - you can always clear that down to some denser, healthier ice surely?
In reply to Chris Reid:
With a longer screw the impact generated from a fall is spread over a larger area of ice and thus less likely to fail?
Maybe if you were climbing a purely horizontal roof of ice then it wouldn't matter as all the screws have the same thread length and equal resistance/holding from a fall???
With a longer screw the impact generated from a fall is spread over a larger area of ice and thus less likely to fail?
Maybe if you were climbing a purely horizontal roof of ice then it wouldn't matter as all the screws have the same thread length and equal resistance/holding from a fall???
In reply to Ben.W:
Methinks a picket effect argument - same amount of thread same area?
Enquiring not arguing but interested in what people think as I've had this notion for a while (hence not buying more than one long- 20cm - screw)
Methinks a picket effect argument - same amount of thread same area?
Enquiring not arguing but interested in what people think as I've had this notion for a while (hence not buying more than one long- 20cm - screw)
In reply to Chris Reid: Come on Chris, you know size matters!
In reply to Chris Reid:
its common sense (as well as basic mechanics) that if the threads are so important, then them being deeper into the ice will have an effect.
i think what you really should say is that if the ice is good enough to hold a fall with a short screw, then why use longer
> If (as BD research suggests) ice screws hold predominantly through their threads and not the "picket" effect - and the threads on ice screws all seem to be the same length, why bother buying longer ones?
its common sense (as well as basic mechanics) that if the threads are so important, then them being deeper into the ice will have an effect.
i think what you really should say is that if the ice is good enough to hold a fall with a short screw, then why use longer
In reply to Chris Reid:
Last year while I was in Ouray, I witnessed someone testing ice screws by dropping a 50-ish (I think, I can't remember) weight onto them statically in a factor 2 fall. We spoke to the guy and his conclusions were:
The quality of the ice is the over-riding factor. Screws in crappy ice or that had been placed too close together failed regularly
Longer screws did hold more often than short screws, although I don't know what the mechanics behind this was
Screws usually failed by pulling out rather then breaking
Longer screws tended to bend, usually one or two inches along the shaft from the hanger. The did not necessarily mean failure
The second most common form of damage to the screws is failure of the hanger
The guy professed himself to be quite impressed with stubby screws, although the longer ones are better if you can place them
The guy was quick to point out that this level of unloading is highly unlikely to occur in a real scenario because you shouldn't be factor 2-ing a single unequalised screw, and you certainly shouldn't be doing it on a static line! However it was scary to watch how many screws were popping out the ice, or more frequently ripping a big chunk out the ice (the screw would remain within the placement, but a big lump would come off still attached to the screw). Most of those screws were either bent or had no visible damage (although he was taking them away for proper analysis and I don't know what the outcome was). It was particularly scary as this was Ouray in a fat year and the ice was good quality. Suffice to say there weren't many people leading in the area that day!
The over-riding message though was that it doesn't really matter what you place so much as where you place it. Make sure the ice is solid and check you aren't too near old placements.
The guy was going to publish somewhere, I believe in a scientific or engineering journal rather than a climbing mag, so the data should be available, although I can't remember where it was .....
Last year while I was in Ouray, I witnessed someone testing ice screws by dropping a 50-ish (I think, I can't remember) weight onto them statically in a factor 2 fall. We spoke to the guy and his conclusions were:
The quality of the ice is the over-riding factor. Screws in crappy ice or that had been placed too close together failed regularly
Longer screws did hold more often than short screws, although I don't know what the mechanics behind this was
Screws usually failed by pulling out rather then breaking
Longer screws tended to bend, usually one or two inches along the shaft from the hanger. The did not necessarily mean failure
The second most common form of damage to the screws is failure of the hanger
The guy professed himself to be quite impressed with stubby screws, although the longer ones are better if you can place them
The guy was quick to point out that this level of unloading is highly unlikely to occur in a real scenario because you shouldn't be factor 2-ing a single unequalised screw, and you certainly shouldn't be doing it on a static line! However it was scary to watch how many screws were popping out the ice, or more frequently ripping a big chunk out the ice (the screw would remain within the placement, but a big lump would come off still attached to the screw). Most of those screws were either bent or had no visible damage (although he was taking them away for proper analysis and I don't know what the outcome was). It was particularly scary as this was Ouray in a fat year and the ice was good quality. Suffice to say there weren't many people leading in the area that day!
The over-riding message though was that it doesn't really matter what you place so much as where you place it. Make sure the ice is solid and check you aren't too near old placements.
The guy was going to publish somewhere, I believe in a scientific or engineering journal rather than a climbing mag, so the data should be available, although I can't remember where it was .....
In reply to kathrync:
Yeah but i weigh a lot more than 50 kgs too
> (In reply to Chris Reid)
>
>
> The guy was quick to point out that this level of unloading is highly unlikely to occur in a real scenario because you shouldn't be factor 2-ing a single unequalised screw, and you certainly shouldn't be doing it on a static line!
>
>
> The guy was quick to point out that this level of unloading is highly unlikely to occur in a real scenario because you shouldn't be factor 2-ing a single unequalised screw, and you certainly shouldn't be doing it on a static line!
Yeah but i weigh a lot more than 50 kgs too
In reply to Chris Reid:
I can't remember what the wieght was, but it was less than an average adult....however the force generated by a static factor 2 fall were still far in excess of a < factor 2 dynamic fall by an average adult.
I THINK this is the paper
http://www.mra.org/services/grants/documents/Beverly_IceScrews_Final.pdf
They were certainly testing in the right area, and the diagram of the rig for their factor two tests looks like what we saw. I haven't had a chance to read it in any depth though.
If you go to the end there is a conclusions section where they say that stubby screws performed better than expected, but their performance is still outranked by longer screws.
Unfortunately there are no images of the damaged screws they showed us...some of the broken hangers were quite spectacular!
I can't remember what the wieght was, but it was less than an average adult....however the force generated by a static factor 2 fall were still far in excess of a < factor 2 dynamic fall by an average adult.
I THINK this is the paper
http://www.mra.org/services/grants/documents/Beverly_IceScrews_Final.pdf
They were certainly testing in the right area, and the diagram of the rig for their factor two tests looks like what we saw. I haven't had a chance to read it in any depth though.
If you go to the end there is a conclusions section where they say that stubby screws performed better than expected, but their performance is still outranked by longer screws.
Unfortunately there are no images of the damaged screws they showed us...some of the broken hangers were quite spectacular!
In reply to Chris Reid: youtube.com/watch?v=2guWbO0Z_Hc&
In reply to Southampton Tom: I think you might need to look at how ropes work if you are concerned about this... 80kg on a full rope impacts roughly the same as 50kg on a half rope and neither impact the same as a semi-static rope. Lobbing 80kg onto any piece of gear on a static line is a worst case scenario, inluding bolts.
In reply to Chris Reid: This may not be the same for ice screws, but the rule of thumb in engineering is that the load placed on any screw is transfered to its surroundings by the first 3 threads, irrespective of the length of the screw. I guess you could make a comparison that the load in this case would be transfered by the first 3 threads in decent ice. So in theory if the ice is well attached and well supported by surrounding ice, then yes a stubby should be as good as a 22. However as I am sure you know this is not normally the case.
In reply to kathrync:
It would be interesting to see the results of similar tests on typical Scottish ice found on the classic routes!
Also when placed in a thick veneer of ice over several layers of snow and ice which is more typical here as opposed to a thick frozen lake in Canada or the likes!
It would be interesting to see the results of similar tests on typical Scottish ice found on the classic routes!
Also when placed in a thick veneer of ice over several layers of snow and ice which is more typical here as opposed to a thick frozen lake in Canada or the likes!
In reply to Chris Reid: i was always of the belief that in good ice, the threads take the force of the fall - so placing them with the head slightly lower that the teeth is good. but in crappy ice the picket effect (if that is the technical term) is more important - and the screw should therefore be placed with eye above the teeth - in this situation it would make sense that a longer screw is better.
i guess that is part of the reason why longer screws are better in crappy ice.
this could all be wrong and i've no idea where or when i learnt it.
long screws could just be good as the ice is more solid the deeper it gets.
i guess that is part of the reason why longer screws are better in crappy ice.
this could all be wrong and i've no idea where or when i learnt it.
long screws could just be good as the ice is more solid the deeper it gets.
In reply to Chris Reid:
I don't know if you have seen this as well, but it does seem to support your conclusions to an extent. There appears to be only a small decrease in holding power with shorter screws in good ice.
http://www.needlesports.com/advice/placingscrews.htm
I don't know if you have seen this as well, but it does seem to support your conclusions to an extent. There appears to be only a small decrease in holding power with shorter screws in good ice.
http://www.needlesports.com/advice/placingscrews.htm
In reply to Tobias at Home:
Screws are designed to be placed perpendicularly to the ice, so to maximise the surface contact with the ice. The threads counteract extraction, but in most situations the supporting ice take most of the force.
Nope, specially in crappy ice, the extra leverage will increase the forces in the supporting ice, quite likely making it shutter and/or forcing the screw into a downwards position where neither the ice support, nor the threads will be able to hold the fall.
Best course of action in bad ice is to chop a (fairly deep) shelf and place the screw vertically on it with a sling going past the lip and running parallel to the screw.
> (In reply to Chris Reid) i was always of the belief that in good ice, the threads take the force of the fall - so placing them with the head slightly lower that the teeth is good.
Screws are designed to be placed perpendicularly to the ice, so to maximise the surface contact with the ice. The threads counteract extraction, but in most situations the supporting ice take most of the force.
> but in crappy ice the picket effect (if that is the technical term) is more important - and the screw should therefore be placed with eye above the teeth - in this situation it would make sense that a longer screw is better.
Nope, specially in crappy ice, the extra leverage will increase the forces in the supporting ice, quite likely making it shutter and/or forcing the screw into a downwards position where neither the ice support, nor the threads will be able to hold the fall.
Best course of action in bad ice is to chop a (fairly deep) shelf and place the screw vertically on it with a sling going past the lip and running parallel to the screw.
In reply to Mr Lopez:
Wouldn't that risk shearing away the shelf of ice?
> (In reply to Tobias at Home)
> Best course of action in bad ice is to chop a (fairly deep) shelf and place the screw vertically on it with a sling going past the lip and running parallel to the screw.
Wouldn't that risk shearing away the shelf of ice?
In reply to nufkin: If placed properly the pull on the screw/shelf will be downwards, rather than outwards (you may need to shape a little channel for the sling by pulling it downwards and forcing it through the 'crust'). However, taking into account that this is a last resort placement when the ice is crap, there's always the chance that the whole setup will come off...
Oh! And contradicting a bit what i said before, here is a good study testing the stress in the ice when placing screws at different angles http://www.jjgeng.com/html/body_ice_screw.html
It shows that on hard ice there's no appreciable difference between placing screws downwards or flush, but an increase in stress when placed upwards.
When placed in medium or soft ice there's a decrease in the forces exerted on the ice when placed downwards, but yet again, i wouldn't want to trust the threads holding on soft ice...
Oh! And contradicting a bit what i said before, here is a good study testing the stress in the ice when placing screws at different angles http://www.jjgeng.com/html/body_ice_screw.html
It shows that on hard ice there's no appreciable difference between placing screws downwards or flush, but an increase in stress when placed upwards.
When placed in medium or soft ice there's a decrease in the forces exerted on the ice when placed downwards, but yet again, i wouldn't want to trust the threads holding on soft ice...
In reply to Mr Lopez: i don't quite understand how chopping a ledge and placing a screw facing downwards is anything more than an extreme version of screwing in with the teeth below the hanger.
Nice article btw - thanks for the link.
Nice article btw - thanks for the link.
In reply to Chris Reid:
Two observations from out here in Canada, hopefully agreeing with some of the good info/advice on the thread:
1) When it's cold (-20C to -30C) the surface ice gets very brittle and a good thump will fracture off plates to about 15 cm depth easily. Below this, the ice seems better and doesn't fracture. A 12-16 cm screw placed direct into the ice would therefore be exerting all of its stress in the range of depth that is most prone to failure. If the threads take the majority of the load, then the depth of their penetration is critical in this case. I use 19-22 cm screws where I can on days like that, and look for pre-plated areas to put them into.
2) Screws out here cost exactly the same whether they are stubby or full length: e.g. $47 for a BD Turbo express. So you're not paying any more or any less for different lengths. I guess the extra material cost is minimal and allows this pricing structure to be justified, but I'm not too bothered, since compared to UK prices, they're still a bargain!
Two observations from out here in Canada, hopefully agreeing with some of the good info/advice on the thread:
1) When it's cold (-20C to -30C) the surface ice gets very brittle and a good thump will fracture off plates to about 15 cm depth easily. Below this, the ice seems better and doesn't fracture. A 12-16 cm screw placed direct into the ice would therefore be exerting all of its stress in the range of depth that is most prone to failure. If the threads take the majority of the load, then the depth of their penetration is critical in this case. I use 19-22 cm screws where I can on days like that, and look for pre-plated areas to put them into.
2) Screws out here cost exactly the same whether they are stubby or full length: e.g. $47 for a BD Turbo express. So you're not paying any more or any less for different lengths. I guess the extra material cost is minimal and allows this pricing structure to be justified, but I'm not too bothered, since compared to UK prices, they're still a bargain!
In reply to Tobias at Home: ps i found where i got my information from - the intro section of the Damilano & Perroux cascades guide.
In reply to Chris Reid: some screws are designed to deform to reduce loading on the placement preventing them from riping out I think it's grivels
In reply to Chris Reid:
Interestingly there seems not to be huge differences in the pull out loads between say 22cm and 19-16cm screws.
Therefore in the interests of weight and speed, which will undoubtably bring safety benefits, it may seem sensible to opt for middle length screws. (Clearly 1 long one will be needed if drilling threads)
?
Interestingly there seems not to be huge differences in the pull out loads between say 22cm and 19-16cm screws.
Therefore in the interests of weight and speed, which will undoubtably bring safety benefits, it may seem sensible to opt for middle length screws. (Clearly 1 long one will be needed if drilling threads)
?
In reply to Chris Reid: To divert from the original question, what are peoples opinions regarding re-using old screw placement holes?
Its certainly a lot faster than getting your own screw placement started when your a bit desperate to get a screw in but intstinctively it seems like it should be weaker but is that really the case? (assuming your screw isn't of a smaller diameter of course)
Its certainly a lot faster than getting your own screw placement started when your a bit desperate to get a screw in but intstinctively it seems like it should be weaker but is that really the case? (assuming your screw isn't of a smaller diameter of course)
In reply to Chris Reid:
While folk are talking about ice screws what about the larger diameter Camp CE marked titanium ice screws (not the dodgy Russian ones)
I like using them in the softer Scottish ice as they feel a lot more secure than the narrower Grivel and BD ones due to the larger tube diameter or am I mistaken...
While folk are talking about ice screws what about the larger diameter Camp CE marked titanium ice screws (not the dodgy Russian ones)
I like using them in the softer Scottish ice as they feel a lot more secure than the narrower Grivel and BD ones due to the larger tube diameter or am I mistaken...
In reply to pec:
To my thinking rightly or wrongly if it goes in easily it will come out easily. But if the ice has melted, reformed and refrozen and you feel the threads biting it should be at least as good as the orginal placement. These are gut feelings so I'm happy to be corrected...!
To my thinking rightly or wrongly if it goes in easily it will come out easily. But if the ice has melted, reformed and refrozen and you feel the threads biting it should be at least as good as the orginal placement. These are gut feelings so I'm happy to be corrected...!
In reply to Ron Walker: allways gone on gut feeling myself and they are so much lighter ! Back in the day when the gum club had maybe 10 screws in the club these weren t the most sought after !
I took my sharpest scews to Canad a and found then confined to belays only !
Normal scewwa fine for abolo kov s
I took my sharpest scews to Canad a and found then confined to belays only !
Normal scewwa fine for abolo kov s
In reply to Ron Walker: I've done this twice, both times I was having trouble getting my own screw to bite whilst in a strenuous position so it came to a choice between using an old hole or pressing on to the next rest without gear.
I could feel the teeth bite which made me wonder how quickly the ice reforms around the inside surface of the hole and hence whether its safe.
As a general principal I'll stick to only using them in situations as described above unless anyone can point me to research which suggests its ok.
I could feel the teeth bite which made me wonder how quickly the ice reforms around the inside surface of the hole and hence whether its safe.
As a general principal I'll stick to only using them in situations as described above unless anyone can point me to research which suggests its ok.
In reply to Chris Reid:
But do you really want to do that? Placing screws is very strenuous, and first having to clear off lots of ice takes a lot of time and energy...
> (In reply to TobyA)
>
> Anyway, with regard to the aerated ice theory - you can always clear that down to some denser, healthier ice surely?
>
> Anyway, with regard to the aerated ice theory - you can always clear that down to some denser, healthier ice surely?
But do you really want to do that? Placing screws is very strenuous, and first having to clear off lots of ice takes a lot of time and energy...
In reply to Chris Reid:
you get bigger dinner plates with longer screws.
that would suggest that having a deeper placement requires greater fracturing thus stronger?
makes me feel better anyway.
you get bigger dinner plates with longer screws.
that would suggest that having a deeper placement requires greater fracturing thus stronger?
makes me feel better anyway.
In reply to Chris Reid:
Does anyone places really long screws on hard ice? I place the average length ones or short ones when climbing but use the long onces for belays and most important Abalakov (?) threads for abbing. Nothing but a 22cm will do
Cheers
Toby
Does anyone places really long screws on hard ice? I place the average length ones or short ones when climbing but use the long onces for belays and most important Abalakov (?) threads for abbing. Nothing but a 22cm will do
Cheers
Toby
In reply to Chris Reid:
heres a MUST WATCH video about ice anchors!
quite amazing really!
http://video.google.com/videoplay?docid=1863958284744514965
heres a MUST WATCH video about ice anchors!
quite amazing really!
http://video.google.com/videoplay?docid=1863958284744514965
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