Falling on ice screws

[Don_Serl]

I took a pic of my older 22 BD express, older 16 BD turbo, and new gen 13 BD Turbo. I am not sure if they changed the new 22cm screws, but the threads on all 3 were the same:

 

take the photo again with the heads equal to each other (instead of the tips) and with a ruler lying across the screws 2"-3" from the head and your understanding of the relative strengths of screws will be clarified. when a screw of ANY length is loaded in a fall, a stress cone of roughly that 2"-3" depth collapses around the tube. the threads BEYOND the cone are what keeps the screw in the ice - for a 10cm screw, that could be as little as 2cm-3cm. a 13cm screw retains about 6cm-8cm of 'bite'; 16cm-17cm 'standard' screws retain nearly 10cm of bite; and 'long' 21cm-22cm screws 'bite' for 2/3 of their length. but it turns out this 'extra' length is irrelevant - a length of 15cm-17cm gives holding power as good as it gets.

 

as for falls, i swore in the early days never to take a lead fall on ice - but i didn't manage to keep my word. i pitched off an icebulge on the west lion one winter a long time ago when a tool slipped and i barn-doored off - went maybe 30 ft - held by a 6" salewa in solid water-ice. and i fzcked up getting in and out of a set of borrowed wrist leashes on borrowed tools on louise falls once - went maybe 6m or 8m, held by (probably, as i recall the times) an old-style chouinard screw.

 

oh, and i pitched off one more time, but screws didn't come into play. tried Shreddie back in the FA season, pulled both tools outa manky windowpane crap about 2 body-lengths up, landed flat on my back on the start-point ice ledge. probably for the best... coulda gotten hurt if i'd gotten higher... screws don't ALWAYS work...

 

cheers,

[el jefe]

I took a pic of my older 22 BD express, older 16 BD turbo, and new gen 13 BD Turbo. I am not sure if they changed the new 22cm screws, but the threads on all 3 were the same:

 

take the photo again with the heads equal to each other (instead of the tips) and with a ruler lying across the screws 2"-3" from the head and your understanding of the relative strengths of screws will be clarified. when a screw of ANY length is loaded in a fall, a stress cone of roughly that 2"-3" depth collapses around the tube. the threads BEYOND the cone are what keeps the screw in the ice - for a 10cm screw, that could be as little as 2cm-3cm. a 13cm screw retains about 6cm-8cm of 'bite'; 16cm-17cm 'standard' screws retain nearly 10cm of bite; and 'long' 21cm-22cm screws 'bite' for 2/3 of their length. but it turns out this 'extra' length is irrelevant - a length of 15cm-17cm gives holding power as good as it gets.

 

as for falls, i swore in the early days never to take a lead fall on ice - but i didn't manage to keep my word. i pitched off an icebulge on the west lion one winter a long time ago when a tool slipped and i barn-doored off - went maybe 30 ft - held by a 6" salewa in solid water-ice. and i fzcked up getting in and out of a set of borrowed wrist leashes on borrowed tools on louise falls once - went maybe 6m or 8m, held by (probably, as i recall the times) an old-style chouinard screw.

 

oh, and i pitched off one more time, but screws didn't come into play. tried Shreddie back in the FA season, pulled both tools outa manky windowpane crap about 2 body-lengths up, landed flat on my back on the start-point ice ledge. probably for the best... coulda gotten hurt if i'd gotten higher... screws don't ALWAYS work...

 

cheers,

 

ladies and gentlemen of the jury, i believe we've found the winning entry.

[mike1]

Why would they NOT manufacture the threads all the way to the top?

 

Good discussion.

[rob]

Great discussion, I've learned a lot.

 

Why would they NOT manufacture the threads all the way to the top?

 

Well, for one thing, if the threads went to the top, and you had to tie off short, the threads would cut the sling

[mike1]

Great discussion, I've learned a lot.

 

Why would they NOT manufacture the threads all the way to the top?

 

Well, for one thing, if the threads went to the top, and you had to tie off short, the threads would cut the sling

 

Uh... yeah, no shit Rob. This is really a last resort screw placement and I doubt that a screw manufacturer would even suggest this use of their product. I may be wrong, that's why I asked. My question is more of a curiosity on the manufacturing side. It seems the benefit of a little more bight to a longer placement might out way the benefit of leaving a clean portion of the shank for tying off. Maybe they tested both and the difference was negligible... Maybe it’s a stupid question... I have asked one or two in my life.

[G-spotter]

Tying off makes screws fail at ridiculously low loads

 

[Ade]

The biggest thing I took away from Luebben's tests was that there is a huge variance in the failure load and even (comparitive) experts find it very hard to judge a good or bad screw placement. The number of threads a screw does or does not have is a second order effect.