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cracklover
Feb 27, 2005, 7:02 PM
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In another thread, smearhound brought up this point, which was news to me at least.
In reply to: This, from the 2004 Metolius catalog: “Many climbers do not realize that pear-shaped carabiners should only be used in belay-rappel situations. A wide, pear shape is ideal for use in conjunction with a plate-style device. . . or a Munter hitch. . . . If the carabiner is loaded on the spine side of the major axis, it will meet the major axis rated strength. But, if the carabiner is loaded on the gate side of the major axis, you can expect it to fail at half the rated strength. We have tested all major brands and none of the pear-shaped carabiners will even come close to meeting their rated strength when tested on the gate side of the major axis. These carabiners were designed to be used only in conjunction with a plate-style belay device. . . or with a Munter hitch. For clipping into belay station and building anchors, always use a ‘D’ style carabiner. . . . The ‘D’ shape makes loading the gate side of the major axis almost impossible.”
This has little impact (pardon the pun) on the thread in which it was posted (toproping, beginner's forum), but if it's true, this is *very* important for anyone who leads multipitch.
The implications of the above are that a serious leader fall has the potential to break a single locker if that locker is a pear shaped biner.
Here are a couple of examples:
1 - Let's say I'm a couple pitches up, belaying a leader directly off my harness, using a grigri on a locking biner. If the leader were to fall before placing the first piece, they'd fall directly on my grigri. The resulting factor two fall could put something approaching 10kN of force on the biner. And if the grigri were somehow to catch on the gate side of the major axis, according to the above article, that would be approaching the breaking point of the biner.
2 - Again I'm belaying the leader, a couple pitches up, but this time I'm redirecting the rope through a locking biner on the anchor. Let's say the redirect biner is a meter above my grigri, and the climber is five meters above that when he falls. The climber falls ten meters on six meters of rope, for a fall factor of 1.67. The force of the rope is on the order of 5 to 7kN, and the pulley effect of the rope running over the biner means that the peak force felt by that one locking biner is now on the order of 8 to 12 kN. Again, this is enough to approach the breaking point for a pear biner if the rope were running over the gate side of the major axis.
GO
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gunksgoer
Feb 27, 2005, 7:15 PM
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ive heard that biners levered on the nose can break at as little as a few hundred pounds. with this in mind im not suprised that a paer loaded next to the gait would be significantly weaker than if it was loaded near the spine. i use Ds for everything but belaying with an atc/reverso, so im not to worried.
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jt512
Feb 27, 2005, 7:20 PM
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In reply to: ive heard that biners levered on the nose can break at as little as a few hundred pounds. with this in mind im not suprised that a paer loaded next to the gait would be significantly weaker than if it was loaded near the spine.
One really has nothing to do with the other.
-Jay
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cjstudent
Feb 27, 2005, 8:24 PM
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possible i suppose.
Just to add in what i usually do.
- When belaying a 2nd, usually i always belay them up on a munter hitch, off of a well equalized multi-point anchor. The munter hitch in this case is on one biner, a BD Airlock i believe. This is about the only point in time where i rely on one piece of gear, that biner. (and the rope)
- when i am belaying a leader i have a power point on my multi-point anchor, with two carabiners. usually a locker and a non, and both are usually D's. this way, if the said climber was to take a fall directly on the anchor, the force would be put on the anchor, which everything (including the power point biners) being doubled. and i suppose if the power point were to break, the force would go onto me, which i am belaying through an ATC on a Omega Jake biner. (also im attached to the anchor through my rope and daisy)
Thats the way I, and most of the people i climb with do things. I only use one pear type biner and thats for the munter hitch. (which i love the BD Airlock because of the "flatness" at the base of the pear.
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gunksgoer
Feb 27, 2005, 8:25 PM
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In reply to: In reply to: ive heard that biners levered on the nose can break at as little as a few hundred pounds. with this in mind im not suprised that a paer loaded next to the gait would be significantly weaker than if it was loaded near the spine. One really has nothing to do with the other. -Jay
in both situations, the biner is being loaded in its weaker area; away from the spine. its the same leverage in both scenarios
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jt512
Feb 27, 2005, 8:48 PM
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In reply to: In reply to: In reply to: ive heard that biners levered on the nose can break at as little as a few hundred pounds. with this in mind im not suprised that a paer loaded next to the gait would be significantly weaker than if it was loaded near the spine. One really has nothing to do with the other. -Jay in both situations, the biner is being loaded in its weaker area; away from the spine. its the same leverage in both scenarios
Sorry, but it's a ridiculous comparison. One has to do with the weakness of the locking sleave itself; the other, doesn't.
-Jay
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cadaverchris
Feb 28, 2005, 8:10 PM
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i think a few people may be confused about the description of this carabiner weakness.
the original metolius quote is talking about a pear shaped carabiner being loaded on its major axis (that is the long axis). this is strongest way to load any carabiner (as we all know). the weakness comes in when the load is somehow kept away from the spine of the carabiner - the biner is still loaded along the major axis but at the wide part of the pear, the load is applied nearer the gate side of the pear end, rather than the spine.
this is particularly important when rigging munter hitches and clove hitches on a pear shaped carabiner. the load strand of the munter must be closest to the spine (not the break strand). and the loaded strand of a clove hitch must be the closest to the spine. my literature from a AMGA course says that a clove hitch rigged incorrectly will decrease the strength of the carabiner by 25%.
a side note: the point of the D-shaped biner is to force the load to be transferred to the spine of the carabiner. which is how we can safely fall on wire gates.
i hope this helped clear up any confusion in this post
edit for spelling
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adamwvt
Feb 28, 2005, 8:32 PM
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Speaking of pear shaped carabiners, which one of you tech weenies can tell me what HMS stands for, and what does it mean?
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