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Expected Pull-Out Strength For 7 cm Ice Screws in "Good" Ice?
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I am having trouble finding any test data or manufacturer recommendations regarding expected pullout of 7cm ice screws. I am mainly interested in the 7cm Blue Ice Aero, but would be happy for info or test data on other 7cm ice screws. Here is what Blue Ice states in their Non-PPE Ice Screw Instructions (for ice screws with a length of 10 cm or less):
In reality, short screws are used for mainly for lead fall protection. I don't know anyone that solely uses short screws for aid climbing. I get that these screws don't meet the test requirements to be certified as PPE, but it also seems a bit specious to claim that these are "for progression only". |
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Obviously the "progression" language is lawyer-driven. The companies who make these - and the people who carry them - know that they are used to protect leads on thin ice. I think the whole world is curious as to how strong they are (make that "can be" given ideal ice quality. No screw is any good in crap ice.), but I suppose it's just not in the manufacturers' interest to actually do the testing. A low result might scare people away, while a good finding might instill an unjustified sense of confidence in users (especially those new to the game) and therefore upset the lawyers. Many MP regulars know that I make super stubbies for sale and have been doing so since before 7 cm screws became commercially available. I like to think I've made more of them than any other DIYer (110+ and counting). I don't know what my screws are being used for out in the real world, but I can share that probably 1/3 of my customers are buying them in pairs. Doubling up these bad boys has real potential to catch a short lead fall. (Side note - is there anyone out there who can do a pull test on screws? Let's talk!) Personally I consider them as psychological pro and/or as "slow me down" pieces on low angle, thinly iced slabs (which just happens to be my favorite style of ice climbing). Bottom line - as Bill B said in that Blue Ice video: we know people are climbing thin ice; it just makes sense to have hardware that can be used in that situation. And don't fall. Bonus photo - 5 super stubbies protected this lead  |
Gunkiemikewrote: I think it is in the manufacturer’s interest to test their products, but it could be the case that they don’t want to disclose the test results to the public. I think the main issue is that the safety standard for ice screws is outdated and should be revised. Personally, I would like to see the standard allow varying pull out strengths and then mandate disclosure of certification test results in real ice to allow consumers to draw their own conclusions and make their own determinations regarding proper usage. We see this philosophy applied in rock climbing to microcams and micronuts that have much lower load ratings than their larger counterparts. While I can understand the reluctance to give a single numerical rating for pull out strengths in a variable medium, keeping climbers ignorant of the limitations of the gear that they are using doesn’t help advance climber safety. There have been published ice screw tests by Marc Beverly and others, but I haven’t seen any test results for 7cm screws. I would be happy to do my own testing, if I can borrow a load cell from someone. |
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As a first approximation, the ice screw length is proportional to failure load, so you can extrapolate from the failure strength of your stubby's bigger siblings. (Presuming the diameters are all the same. I'd be so delighted is someone would manufacture a stubby, fat ice screw...) The "progression" language is more than lawyerly. I'm guessing that anyone who doesn't always drive at/below the speed limit understands that part of not driving the speed limit is lawyerly--that you might get a speeding ticket, that you might be extra liable in the event that you injure someone/something while speeding. And also understands that part of the speed limit posting is to identify an expectation that enables drivers to manage risk. (And the nerdy speedsters might understand the relationship between speed limit and physics...) Stubby ice screws in good ice are in the range of "... cannot be relied upon to withstand the highest forces that could be generated in a fall" to "cannot be relied upon to withstand typical forces generated in a fall." See page 9 of http://web.mit.edu/sp255/www/reference_vault/McMillan_how_strong.pdf . "For progression only" should alert climbers that the stubby ice screw anchor cannot be relied on and that appropriate risk management strategies might be in order. I am happy to be able to take advantage of the utility of "for progression only" ice screws beyond slow-me-down/psycho-pro. Being able to back down to gear I can hang on with body weight, being able to rappel/lower, being able to place two "for progression only" ice screws--one on each of a double-rope pair are all 100% legit strategies to manage risk with stubby ice screw, opening up ice climbing opportunities, and easing a worried mind. |
dave custerwrote: Blue Ice's 7 is fatter than CAMP's or mine. It should absolutely be tested alongside the more typical diameters. QUESTION TO THE READERS - Who'd be interested if we did a "crowd sourced" test program? |
dave custerwrote: The maximum load on anchors is highly dependent on the ”fall factor”. Petzl wrote up a nice study on the peak forces measured on anchors for a few different fall factors (https://www.petzl.com/US/en/Sport/Forces-at-work-in-a-real-fall). If we take the peak force measured by Petzl for a 0.3 factor fall (~4 kN) and compare it to the expected pull out strength of a 7cm ice screw (currently unknown), then we can gauge whether a 7cm ice screw or multiple equalized 7cm ice screws is likely to hold a 0.3 factor fall. In practice, the thin ice encountered on a pitch may be well above the belay and thus the peak forces on lead protection may be significantly less than the minimum 10 kN (EN standard) or 9 kN (UIAA standard) strength requirement for ice screw PPE certification. So, there is very good potential use case for using shorter screws for lead protection, when the fall factors are relatively low. |
Karl Henizewrote: Agreed. There are lots of use cases for exceeding the speed limit. Try to avoid getting pulled over on account of violating Newton's laws... |
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Hello Karl! |
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These aren't 7cm stubbies, so it's not a direct answer to your question, but it is a interesting watch from Hownot2 https://www.youtube.com/watch?v=Hy_W10xMrCM https://www.hownot2.com/post/ice-screw-break-tests-in-iceland |
High Mountain Gearwrote: A couple weeks ago someone climbing near me had screamers for every screw placed… in good ice. I was intrigued, and confused. I think one problem with trying to get a better rating method for screws is that they aren’t tested in ice but a particular concrete matrix. I’m sure it’s done for repeatability, but manufacturers will say that they don’t always see things translate from the test substrate to ice. So if you’re tying to be too fine, it could be misleading and that’s worse than having no info. |
yukonjackwrote: Cool video, thanks! |
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I think this video from Black Diamond explains why. Basically the ice starts to give and the screw shears off before the threads - about 5cm due to the metal fatigue rather than the threads failing. A 7cm screw that breaks at 5cm… https://www.blackdiamondequipment.com/en_CA/stories/qc-lab-aluminum-vs-steel-ice-screws/?fbclid=IwAR2YxkPO5HAB-6CfJScUYCtUtQCwsRGL1RDeeqp-i5Uw_K0_slftwAq5oRw |
High Mountain Gearwrote: I’ve carried Screamers ever since they were Air Voyagers. Rarely use them except just as a draw. A lot of testing suggests that the successive shocks as the threads blow negate any benefit except in some rare situations. You should be climbing on skinny double ropes anyway, which should offer a little more margin for error anyway. Oh yeah, don’t fall. |
bearded samwrote: According to Blue Ice, the 7cm screw has a “placement length” of 6cm. The shorter screws are more likely going to pull out, when the ice fractures, rather than remain in the deeper ice. So, the black diamond QC lab description of the ice screw failure mode when pulled radially probably doesn’t apply to shorter ice screws. |
High Mountain Gearwrote: If you look closely at the photo I posted above, you'll see Screamers on the first two screws. |
bearded samwrote: While this BD video doesn't say what load the screw needs to see to snap the tube, we can assume that is occurs above the rated 10 kN. Field testing by others (Mark Beverly IIRC, and certainly HowNot2) confirms this. So again, this is irrelevant to real world screw performance. |
Gunkiemikewrote: I am somewhat distracted with other projects... what is the ideal artificial ice testing method? Freeze ice block inside welded metal frame...insert screw, pull? How much volume is required to adequately test this, or is this an outdoor onsite test only? Indoor I could get done with load testing, outdoor in WA is, well, not going to happen. |
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We have done a bunch of testing, but I can't talk about it. The reason is it's variable. Real ice is hard to test without encasing the ice in a steel frame, and is that really representative? The cellular concrete we have to use for the CE test is more consistent but it ain't real ice. When you test stoppers, cams, and micro nuts, you use steel fixtures. I'm not sure that's representative either but maybe it's closer to reality. Testing in lake ice, as Marc has done, might be the closest thing to consistency with actual ice climbing, but I have my doubts about how well it translates to thin ice on rock strength. More work on testing standards and fixtures are being by the UIAA in concert with the manufacturers. Small nuts are rated to only 2kn, along with small pins. They have saved my ass more than once. When in doubt, you put in a few, equalize, and clip them to skinny ropes to keep the forces low. Do the same with super stubbies. I know there are some out there who feel that selling these with little strength data (or as progression only) is not responsible.....all I can say is that we wouldn't be doing it unless we thought it had merit, since we climb this shit too. And since it's the holidays, I'll add one more thing from Jesus. "Let he, who has never run it out on thin ice, cast the first stone".... Gotcha! Be safe out there. |
Bill Belcourtwrote: Marc subsequently performed drop tests on waterfall ice at the Ouray Ice Park. While Marc’s published testing doesn’t address the “thin ice on rock” scenario, I do believe that this type of published test data is still valuable for climbers, despite the large variability in testing on waterfall ice. |
