VT Hitch Anyone?

Is the VT hitch as the backup (installed above the rap device) gaining any traction (he he) with this group? I picked up the Bluewater 8mm VT Prusik cord after reading a related thread last September. It's pretty quick to form (in my experience quicker than a prusik, slower than my go-to autoblock), it's cool the way you can push the VT hitch up the rope to position it to take the load, and the fact that (with practice) you can gradually release it under load and slide down a weighted rope is its special power. This is great for a knot pass, but that's a pretty specialized use case, and for general purposes it hasn't replaced the lower-profile hollow-block my harness. 

The VT hitch knot-pass technique is described on p. 386 (diagram 310) of AK's Down. Elsewhere in the book, he calls the VT hitch "one of the most useful friction hitches in your arsenal" (p. 98). But on p. 227 he says "The only time I use a high [i.e. above rap device] back-up-hitch is when passing a knot, using a VT hitch . . ."

what's its advantage over a klemheist?

If you push down gently on the top of the fully-loaded VT hitch, it will slide down the rope gradually in a controlled manner. I think you have to unweight a fully-loaded klemheist to reposition it, but I haven't actually tried that. 

You'll find that the VT is popular with lots of old-school guys or anyone who came into climbing from a rescue background. Nice piece of kit. Its biggest selling point is that it solves some problems that most mountaineers won't run into, which is likely why it never really found its footing in our scene.

Andy Wiesner wrote:

If you push down gently on the top of the fully-loaded VT hitch, it will slide down the rope gradually in a controlled manner.

That just solves a problem that below-the-device backup does not have. While the biggest problem with above-the-device backup is not solved by the VT hitch. It is less advantageous for the normal rappel backup, and more useful in a scenario where you need to release the load (knot passing, load transfer, etc).

aikibujin wrote:

That just solves a problem that below-the-device backup does not have. While the biggest problem with above-the-device backup is not solved by the VT hitch. It is less advantageous for the normal rappel backup, and more useful in a scenario where you need to release the load (knot passing, load transfer, etc).

yea, this is my take too. doesn't really have an advantage in a standard rap setup...

Larry Penberthy developed the below-device backup in the 1970s,  His focus was a bunch of failures of the above-the-device backups in both caving and climbing and subsequent testing.  The problem was (and presumably still is) that when climbers lost control of a rappel (usually because they let go with the brake hand for some reason), they invariably held on with the upper hand and so kept the above-device backup from ever activating.  Putting the knot below the device and in the brake hand meant that the knot would be released---and so activated---if the brake hand left the rope.  Putting the knot back above the device undoes the original rationale for the below-device method.   Novices and maybe not-so-novices will often grab the rope above them with both hands if they slip or swing, and for them having an above-device knot seems like a really bad idea.  More experienced climbers, who have trained themselves to never release the brake hand, will have to decide for themselves if the above-device failure mode is relevant to them, but should be aware that testing showed that no one suddenly subjected to a failure or complete loss of friction will release an above-device knot so that it can function.

The Valdotain Tresse above the device is useful when the main purpose is to go hands-free a lot, as in cleaning gear on rappel. You can ditch the extension and have everything very compactly on the harness belay loop.  It is not, by the way, ideal as an ascending knot, because of the way it extends to grab, losing some precious upward progress each time the knot is advanced.  

The main advantage of the VT is its releasability under load, a property it shares with the autoblock, so you could put an autoblock above the device too.  I do not know whether one of these knots is significantly better than the other for that application.  The tree guys are fond of a VT as part of a progress capture system in which the VT releases when it collides with a pulley.  It would work well for improvised haul systems in climbing too.  

As for sliding down a tensioned line, I'd be super cautious about using it for that, There was a thread on MP a while back in which someone reported falling the length of the rope after being instructed to descend using a pressured VT. I haven't tried it (and don't intend to), but my guess is that there is a tiny difference in pressure between a controlled slide and complete release. In a climbing emergency that requires a descent of a taut line, I think prusicking down is the only viable alternative,

[Strike this.  See comment by aikibujin  below. Contemporary climbers are, in some cases, defeating the Penberthy rationale even though they are using a below-device knot. This happens with a rappel extension when the climber drags the backup knot down with the non-brake hand. In this case, the system is only slightly better than an above-device configuration (slightly better because the knot doesn't have to hold full body weight).]

rgold wrote:

Contemporary climbers are, in some cases, defeating the Penberthy rationale even though they are using a below-device knot. This happens with a rappel extension when the climber drags the backup knot down with the non-brake hand.

That's just not true. With below-the-device backup, the friction hitch is on the brake strand. Rappel extension or not, whichever hand the climber is using to drag the friction hitch down is also A brake hand. A lot of people who use the below-the-device backup often have both hands on the brake strand, because there is now no need to grab the rope above the device. If you lose control of the brake strand and let go, the friction hitch will lock up; if you death-grip the friction hitch, you're also grabbing the brake strand hard which give you control. It is simply impossible to let go of the brake strand AND death-grip the friction hitch at the same time with a below-the-device backup. But that scenario is possible and potentially deadly for the above-the-device backup. That's why below-the-device backup is more than just "slightly better" than above-the-device backup.

A VT won't work for rapping down a fixed line; that's just not what it's for. They just don't grab the rope uniformly when used with full body weight. I've never tried it above my descender, but on a gut level, I wouldn't trust it. 

The only advantage I can see to it is that you'd be able to rap without extending, but you'd want something to anchor you in when you're doing multiple raps. So maybe it'd be good for rapping single pitch routes? Maybe I'll give it a shot next time I'm using a friends' eye to eye cord.

aikibujin wrote:

That's just not true. With below-the-device backup, the friction hitch is on the brake strand. Rappel extension or not, whichever hand the climber is using to drag the friction hitch down is also A brake hand. A lot of people who use the below-the-device backup often have both hands on the brake strand, because there is now no need to grab the rope above the device. If you lose control of the brake strand and let go, the friction hitch will lock up; if you death-grip the friction hitch, you're also grabbing the brake strand hard which give you control. It is simply impossible to let go of the brake strand AND death-grip the friction hitch at the same time with a below-the-device backup. But that scenario is possible and potentially deadly for the above-the-device backup. That's why below-the-device backup is more than just "slightly better" than above-the-device backup.

Yes, good points!

Modern tree workers are switching to the Michoacán, same easy releasing, but it is more compact and isn’t as dependent on the hitch leg length to work properly. The hitches will release but with multiple loading and unloading cycles they will bind up, the Sticht Hitch being an exception.