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Mark O'Neal

Ice screw length

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The more screw/ice surface contact the stronger the anchor. So it makes sense to take the longer screw if you have no idea what condition you may be faced with. You cover all your bases and you could always sling the screw if placing it in a shallow spot.

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you could always sling the screw if placing it in a shallow spot.

 

Am I understanding you right? If the screw is too long and can't go all the way in to the hilt, you can sling it? Sling it where? At the ice line around the screw? I think I'm missing something because it would seem like the threads on the screw would be kinda sharp.

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The threads don't go all the way to the end. Plenty of room to girth hitch a sling - check out some books and articles for pics and details.

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Some tests were done by Leubben involving slung screws and unslung screws that were partially driven. What he found was that in a big fall, the unsupported part of the screw bends, the sling slides to the head and the hanger cuts the sling. If the screw is not slung, the screw bends, and it either fails or doesn't fail, but at least you don't have to worry about the sling getting cut.

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Bury you screw all the way. Bring two if need be. I'm fumbling to remember where I saw one of the best articles in a while on this stuff recently.

 

"How to Ice climb" by Chris Luebben, was pretty sweet on describing different fall senerios (pp. 144-148) Just looking again, I'm remembering that a long screw is not always your friend (insert joke here). Lots of cool pics of 22cm screws bent to heck, and the poundage of falls listed below the pics. Good news is that often the carabiners broke first, which means that there where some pretty big fall factors going on.

 

 

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For that scenario, no question in my mind....10 to 13cm. Tying off screws is pretty much left to the unprepared or desperate these days. Although I thought it a resonable idea twice in one pitch this week :eek:

 

Only reason I still own a couple of 22s is to cut V threads.

The threads give the holding power not the length of the screw.

 

But you can forget the V threads with a 13cm screw if you weigh more than 100#..btdt as well. Didn't work well. The newest generation of screws also preserve the ice (and its strength) during placement much better than the old days. Small blobs of good ice that will take a 13cm screw might well do the trick.

 

If you disagree read these links and goggle Craig Lubben...not *Chris*.

 

http://www.terragalleria.com/mountain/info/ice/bd-test.html

 

http://www.grivelnorthamerica.com/headlines.php?id=1&GrivelSess=b5803cb72430edd7ed2423fe3e973fdd

 

http://www.mra.org/services/grants/documents/DynamicShockLoadEvaluationofIceScrews_Final.pdf

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The more screw/ice surface contact the stronger the anchor. So it makes sense to take the longer screw if you have no idea what condition you may be faced with.

Almost all the holding power of a good screw comes from the outer threads of the screw (closer to the hanger). Moreso, the actual thread length on 13 cm and 22 cm is pretty similar (or identical i think). Your statement is only true if the surface ice is bad, but the underlying ice is decent. Even then, you could clear the surface ice. On a mixed alpine climb where the choice was between one screw and zero, you are far more likely to find thin ice <13 cm vs >22cm. In that situation, the completely driven 13cm screw is much stronger than a half driven 22cm screw.

 

You cover all your bases and you could always sling the screw if placing it in a shallow spot.

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Ah, see I knew I was missing something. You gotta love Google. They have the Luebben book online and I jumped right to the pages of interest.

 

I'm not anticipating a big leader fall. I'm thinking I could be on a 45-50° slope and want to put a screw in, either as piece of mind fall protection or to rap down. I suck at making V-threads btw.

 

So would the consensus be a 13cm?

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I haven't tried this myself, but I read that it's better to use a wire nut to sling the partially driven screw. Push the wires up past the plastic thing that holds both wires together, sling it around the screw and choke it down. Has anyone tried this method?

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