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Myths, Cautions & Techniques of
Ice Screw Placement
Chris H. Harmston MSE
All this data is from screws placed within 5 degrees perpendicular to the ice surface. As can be seen from Table 1 there is a very large spread in the data, reflective of the fact that not all ice is equal.
Does this data mean that you should always place the longest possible screw? Mostly, but not necessarily. There are several factors to consider. Assuming that the ice is thick enough for any screw, the placement should be strongest with the longest screw. How much surface ice did you have to remove to uncover good ice and how much good ice is left? How pumped are you while trying to place the screw? Is this the only piece of protection you are likely to get for some distance? How far out from the ground or belay are you?
My recommendation is to place the length that makes you most comfortable in terms of protection level and pump factor. When you are close to the ground or belay you have the potential to generate more force on your protection. Make these placements as bomber as you possibly can. In other words, use longer screws when close to the belay or even equalize two placements if you are unsure of the quality of the ice.
Comments on Ice Quality by Alex Lowe
"Good work on the screw research. Having read it and thought about the mechanics of pulls along the axis of the screw as opposed to loading such that shearing through the ice plays a role, it makes intuitive sense that a screw placed at a positive angle should indeed hold better, but only in ideal ice conditions - that's the big qualifier. Of course determining what constitutes "ideal ice conditions" is the art and essence of placing ice gear. I felt you made this clear in your article. My personal conclusion from your tests is to place screws at a positive angle when I feel the ice is 'very solid'. Obviously some rather ill defined terms in that statement! 'Very solid' will remain an intuitive assessment. But here are some attributes I associate with 'solid' ice.
1. Appearance: Ice that is clear (glassy) in appearance usually contains less air, thus having greater density. Grayish, opaque ice is often shot through with air bubbles and thus is less dense and has less ability to support a screw placed at a positive angle. (At what declining density though does positive angle yield the advantage to zero or negative angle?) The effect your ice tools have had on appearance as you've climbed toward the screw placement is also informative. Pick holes will reveal brittleness, plating and layering and other indicators that affect my assessment of ice quality.
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