Ice climbing top rope? Consider a V-thread
Photos from Tim Banfield @timbanfield and article (used with permission) are from Sean Isaac. Sean is an ACMG (Association of Canadian Mountain Guides) certified Alpine guide, a former professional climber, and author of the “Ice Leader Field Handbook” and “How to Ice Climb” (2nd ed.) Follow @seanisaacguiding and @howtoiceclimb for more great tech tips.
From Sean:
“It’s shocking how fast ice screws can melt out on a warm (> 0 C) day especially when under tension in a top-rope context. Even on very cold days, direct solar affect at the critical angle of incidence will loosen ice screws quickly.
I’ve seen top-rope ice screw anchors melt out on -25 C days in January in 30 minutes due to the sun. If warm temperatures or solar exposure is anticipated then melt out should be a concern.
Using bolted or tree anchors is the obvious solution, but if an ice anchor is the only option then mitigate melt out by using V-threads instead of ice screws for one or all anchor points. The nylon cord/webbing does not conduct heat like metal screws so therefore do not melt out as rapidly.
It sometimes can take days for V-threads to melt out. The cord can then be retrieved at the end of the top rope session and a no-thread used to rappel.
Packing snow over the top of ice screws is not a recommended treatment since it does very little to negate melt out”
Some V-thread considerations:
Threads should never be used as a single-point anchor. Make a second point as show here (screw or another thread), and equalize them.
Threads should be made with a 21-22 cm screw.
All angles are 60 degrees making an equilateral triangle that is as deep as it is wide.
Aluminum screws make constructing V-threads easier due to their larger tube diameter.
7mm cord is the minimum recommended diameter. Not because of its strength but because of it’s surface area.
Webbing makes a stronger thread than cord, due to its broad surface area spreading the load at the back of the V.
Horizontal threads test at an average of 11kN in good quality ice.
Vertical threads (A-threads) tests 3kN stronger because most of the force is on the upper hole, placing more total surface area in compression in a single vector.
Remove cord from threads when possible to minimize plastic garbage in the mountains.
V-thread equalized with single screw.
Another option: use a pair of V threads. If you carry a cordelette that's open (a.k.a. untied), you can thread the end through ALL the holes and tie it off. #CraftyRopeTrick!
