Hello, Brad--

I don't have an answer for you, but I do have some questions/thoughts:

1--Could moisture/humidity have anything to do with it? Has that been different?

2--How much did it slip? I assume that you grabbed the rope to stop the descent--did that take much work on your part?

3--Is it that the knot would hold you in place until you "pushed" on the top of it (to begin your descent), and then it didn't catch and hold once you took your hand off the knot?

4--How much do you and your gear weigh? And that prompts the thought, are you carrying more weight aloft now?

If #3 is true, then the answer from the engineering and physics worlds is that the dynamic coefficient of friction of the knot is too low to hold you, whereas the static coefficient of friction is high enough to hold you. What that refers to is that the frictional force may be enough to hold you *until* it begins slipping, but once the slipping has begun, it ain't gonna stop. I'm sure you've experienced that when pushing a heavy _object_ across a floor: you have to push with a certain amount of force to get it started moving, but once it is moving, you don't have to push as hard to *keep* it moving; and once it has stopped, you have to push harder again to get it going.

Of what value is that to you in your situation? Probably none, but you did get a free physics lesson. The next time it slips, instead of screaming and grabbing for the rope, you can calmly say, "Dear me--the dynamic coefficient of my Blake's hitch is too low."

Seriously, the knot does need more friction. Why now and not before? Beats me.

You commented that you were uncertain as to how tight it should be; I snug mine down pretty tightly--no slack.

I'm looking forward to hear what some who have experience with XTC, and others with a ton more experience than I have, might have to say.

Good luck!

Jim