Warning: Long Post with several images... some depict what not to do (IMHO).
I've been forming an opinion about different ways of locking off with a closed frame micro rack that has a single hyperbar. I'm wondering if any of you would like to weigh in as well. Basically, I'm trying to decide on what I feel most comfortable with in terms of both full and soft locks. All of these locks are described in the literature, the instructions that came with my rack (a BMS) or were shown to me/observed in use by some other caver. I've hung on all of them (a foot or two from the deck). I'll go through them in order giving my thoughts on them, but like I said, I'm hoping for some input.
BMS refers to this as a "Soft Lock" in the paperwork that comes with their micro-rack. This paperwork can be found here. Here is a photograph of the same thing:
I've seen a variation on this one as well. The difference is to bring the tail over the top bar between the bolts first and then bring a bight through the rack frame (under the bars) and then loop it with a twist over the hyperbar.
It looks like this:
Of these, I think I prefer the first because your rope will always end up in the high friction position over the hyperbar as you are unlocking it. It ends up between the bolts with the second version.
Question. BMS calls this a soft lock. It seems kind of like a full lock to me. Is there more you should do if you want to lock off more securely than this? The only thing I can think of would be to tie off afterwards by bringing a bight to the top of the frame and tying it around the rope. This is in some ways similar to the full lock off pictured in "On Rope" on page 123 (figure 5-54 B).
In any case it would look like this:
Is it overkill, or is it necessary?
Other Variations: These come from "Alpine Caving Techniques" (more or less) from the discussion on locking off with a hyperbar on pages 146-147. Please note that their description seems to be tailored more to a j-frame rack with a hyperbar. Start with a soft lock like this:
And then fiinish by passing a bight in the tail around the back of the rack, through the frame (under the bars), and then loop it over the hyperbar with a half twist. It should look like this:
This seems ok, but I was able to partially unlatch one of the bars when practicing a changeover using this lock. It happened where the bight passes around the left side of the rack before coming back through the frame and over the hyperbar. I noticed it after placing the rack on the rope, removing the croll, and partially weighting the rack. It only happened once, and I have not been able to reproduce it.
I was shown a variation on this lock that involves passing the bight of rope through the locking carabiner instead of the rack frame. It looks like this:
One thing I noticed about this lock is that while it seems to work ok when you are already on rappel and the rope is loaded, it strikes me as a really awkward one to use during a changeover. This is because you are not weighting the rack when you are installing it on the rope. This makes it possible for the carabiner to get bunched up with the bars when you install the rack and lock off. It looks like this:
Two things I don't like about it: (1) you could be running a little risk of cross-loading your carabiner if you aren't careful (2) When you weight the rack, the carabiner has to pull the rope back down to the bottom of the rack frame. Sometimes, this isn't a very smooth motion. For this reason, I'm hesitant to use this lock with a micro-rack.
So I guess my tentative preference would be to use the BMS "soft-lock". What about tying it off? Is this ever necessary? What would you use?