Anchor Technique Using a VThread

Since the mid-1970s I've been using an anchor technique called a V-thread, primarily for rappeling to avoid having to leave behind screws or sections of conduit. A V-thread is faster and easier than cutting a bollard, which is also a clean technique. A V-thread is made by placing two screws about six inches apart and angling them so that the holes will meet as far

Plins »N rtrw^i the V (Photo: Ion lmlmsMl

back in the ice as possible. After placing the first screw, back it out most of the way and use it as a sight for placing your second screw. You wilt feel the second screw turn more easily when it intersects the first screw hole. Remove both screws and poke a sling into one hole, using a tool fashioned from a 12-inch length of hanger wire with a carabiner eye in one end and a quarter-inch hook at the other. Then reach into the other hole and hook the end of the sling through.

Clip a carabiner into the two ends of the sling, and you have a very solid anchor for lead protection, belays, or rappels. In solid ice, the V-thread tests to well over 2,000 pounds. A flat sling spreads the force over a larger surface area than a cord would and takes longer to melt through, which is the typical mode of failure. An 8mm or 9mm rope can be passed directly through the V for absolutely clean rappeling, but if there is any melting, freezing, or running water near the hole, use a sling to avoid the rope freezing into the ice.

A «mAincr dipped into the two endi ol the slmg {Photo: Ian Towlinion)

Thin-ice Protection Using Screws in Series

Reliable thin-ice protection can be had by placing screws in series, This is a technique I borrowed from the multiple-stake set-ups used to anchor circus tents in soft, shallow ground, Place two screws, one directly above the other, about 18 inches apart. As soon as the screws bottom out against the rock, stop turning. Back off a partial turn on the lower screw, so the eye is pointing directly up. I carry a five-foot length of 7mm static cord with a six-inch loop tied in one end. Tie off the upper screw using the loop. Run the cord down through a carabiner in the eye of the lower screw and back up through the bottom of the tie-off loop. This achieves a mechanical advantage for pulling tension between the upper and lower screws. Pull quite hard and lock the cord off with a series of trucker's hitches below the tie-off loop. When properly done you will be able to strum the cord like a bass fiddle string. Finally, with a separate sling, tie off the lower screw flush to the ice and clip your climbing rope through a carabiner here,

Since ice screws fail by successively fracturing surface layers of the ice under tension until a shear force is converted primarily to a direct outward pull, screws in series provide a unique advantage. The tension from the upper screw keeps the lower screw from flexing downward and, since the upper screw can withstand a force of several times that which is applied to the eye of the lower screw through its lever arm, in most cases the tip of the lower screw must shear through the ice for this arrangement to fail. Even weak, thin ice is very strong in resisting a shear force. In tests, screws in series resist several times the force of two screws tied off and equalized, The security of the arrangement can be even greater if a force-limiting Air Voyager or Screamer sling is applied between the lower screw and the rope.

Strawi placed in terlei (Photo: Brad Johnson 1

Because longer screws work best in this technique, I seldom carry any screws less than seven or eight inches in length.

Strawi placed in terlei (Photo: Brad Johnson 1

Continue reading here: The Northwest Spur of Mount Hunter Alaska

Was this article helpful?

0 0