Following TCI's guides of having a rescued individual's weight primarily on their own rope, I would say yes. Because obviously, we got into the tree somehow, so our knots have been holding each of our individual 350 lb. weights. There shouldn't be any real difference between the stress on the rope while climbing and being rescued/rescuing. Does that make sense to anyone besides me?

JOsh

Makes sense to me.

Suggests that I pose my original question again:

What is the weight limit for safely descending on a friction hitch with a dynamic climbing system?

Nick's idea of testing this myself may have to suffice as a single point of information, although I would be surprised if I were the first to perform such a test. Suggestions about performing this test welcome; I don't like the idea of using myself (or anyone) as weight for this test, since to find a limit I must produce at least one rapid, uncontrolled descent.

Brad

TCI uses a Rescue Randy to train with rescue techniques. Randy is plastic with articulated joints (used by fire depts.) and weighs 145 pounds. One rescue technique we have practiced in the past is to climb up next to the victim, clip him to our harness, and then cut the bridge which puts his weight full on the climber doing the rescue. We had a ground belay holding the rope on the ground (DRT system). The shock on the climber was less than I thought. The friction hitch held fine (B-53 knot – Blake’s with 5 wraps and 3 tucks). It made for a jerky ride down though. We do not practice this _style_ of rescue anymore. We put a carabiner above the victim with an adjustable knot (pick off strap, lanyard with ascender, or daisy rope) and let our descending weight pull down the victim’s friction knot automatically. It is easier to cradle the victim while descending using this system.

To test for the limit I need to define a "safe, controlled descent", maybe in terms of distance slipped before hitch holds. Is there a common definition for this that I could use? How would you define this for this test?

Brad

Bradley Ford says:

To test for the limit I need to define a "safe, controlled descent", maybe in terms of distance slipped before hitch holds.


My experience with "rescues" both in training with TCUSA and when assisting climbers with disabilitites, is that if the Blake's slips, it is going to keep on slipping. I haven't experienced it sliding for a while, then catching. (Using a 5-3 Blake's). It would seem that you could use a Munter hitch on the down rope to slow yourself even more.


From the original post, it sounds as if you want to know the holding power of a knot if you clipped the other climber to your belt and now had their full weight and your full weight on your knot system. It sounds as if you're trying to prepare in advance for something happening in the tree, which is good. But I'm not sure that you can get a definite weight limit that will work in all circumstances (as you pointed out in your first post). Having a specific TECHNIQUE(s) that would accomodate a myriad of circumstances may provide you with the best (i.e. safest) result.
Maybe you could do some tests in different circumstances (diff knots, diff amounts of wraps on Blakes, diff types of trees, wet vs. dry rope) and then post the results?