The recent discussion about the Spider technique to reduce the friction in the Blake's hitch during descending made me think.
I usually climb on a 5-3 Blake's rather than a 4-2. It seems to hold me better without any slipping when I am climbing up. It seems that an extra wrap of the Blake's hitch provides more friction when holding my weight on the rope. Yet, to me, it would seem that while descending, a 5-3 would have less friction per unit surface area in contact with the down rope than would a 4-2 (i.e., 3 wraps provide less friction AT EACH WRAP versus 2 wraps - it spreads out the friction). My weight is the same in either system, so on a 5-3, one third of my weight is on each wrap, with a 4-2, one half of my weight is on each wrap. Thus, you'd have a potentially lower risk for burning out the knot by using a 5-3. It sort of seems like a paradox - a 5-3 gives more friction while going up, but spreads out the friction (and heat) more when going down. Am I thinking of that incorrectly?
It seems like you're thinking no the right track but I don't believe that there is a linear relationship between wraps and friction. Without doing a myriad of tests with different ropes and cords and number of turns it isn;t good to make a statement. Do what works for you. Most pro arbos use a three or four wrap BH.
Originally posted by Tom Dunlap
Without doing a myriad of tests with different ropes and cords and number of turns it isn't good to make a statement. Tom
That makes sense, but is there a generalization that you (or anyone else) would make? Or, to put it another way, would YOU choose a particular way to tie your BH if you knew that you were going to be making a long descent on the BH (and not using a Spider-type descent system)?
(i.e., 3 wraps provide less friction AT EACH WRAP versus 2 wraps - it spreads out the friction).
So in the Blakes the bottom wraps provide the friction? I've been using distals and schwabish assymetrical clove hitch/prussiks, and it seemed to me that the takehome lesson was that for there, the upper wraps hold the friction.
I'm tempted to agree that you theoretically are spreading that heat over more rope, but maybe the dangerpoint of abrasion is always the bottom most point, or the topmost....It may not matter how many wraps there are. You may as well try all the combinations you can think of and maybe let us know your favorite?