One way pulley

Howdy!

I'm not a climber -- I come from a completely different sport (freediving) and I have a question which I think the climbing community would be uniquely suited to answer. I'm trying to devise a safety system which allows one to move bi-directionally on a rope with the least amount of friction until a switch or such on the device is engaged, and then only move uni directionally with the device clamping onto the rope when something tries to move it in the opposite direction. A very key thing would be that it moves with very little friction on the rope when its moving, and not require a lot of force to move around (considering we'll be moving this around on breath-hold hundreds of feet under the water). Maybe something like an ascender?

I'm guessing something like this has been already invented in the climbing world, and I figured I'd ask here.

Thanks!

petzl.com/en/outdoor/self-j…

Welcome!
I used to freedive years ago (hence where my username came from) but have given it up. I wouldn't want anything that is currently made hooked to me and a rope at those depths though. The drag and friction on the rope would be prohibitive. Microtraxion is the most likely product that would work for what you want, but the mechanism that holds the one way capture teeth open is pretty small to be used at those depths and to dis-engage mid dive if it were to get bumped from free flow mode to capture mode.
A lanyard from the weight belt to the device would be the easiest for what you are saying though and could allow retrieval of the diver in a shallow water blackout if the one way action was already engaged. Good luck finding something that will work for what you are trying.
BTW are you talking sled no limits type diving!

The micro traxion might work, but it is designed to have the rope slide in one direction only, ( with very little friction). It has a very small release trigger that really needs to held down at all times to allow the rope to slide both directions. Also the Traxion has to be totally un-weighted for the trigger to work. If you release the trigger, it will side both directions, however any jostling or bumping will cause the device to go back into a single direction mode. It would be sketchy at best to try to operate this thing in the dark, underwater, and with gloves.
If I am thinking correctly of what you trying to do, I don't believe an ascender would work, as they are typically camming devices that require to be weighted to hold the rope. So, if you were in some sort of neutral buoyancy unconscious state, the rope might just slide right through it during the rescue.

The Micro and Mini Traxions sound right.

They can both be locked open so that they slide freely in either direction, or made to slide easily up, but lock when pulled down (by disengaging the lock that holds them open. I forget how it works on the Mini, but on the Micro a push of a button unlocks the cam teeth).

The Micro is especially effortless on the rope.

I have two Micro Traxions and they are awesome. Not sure how being submerged would affect them..,

A Gri Gri maybe? It's bi directional, but wouldn't feed through very smoothly

DrApnea wrote:Welcome! I used to freedive years ago (hence where my username came from) but have given it up. I wouldn't want anything that is currently made hooked to me and a rope at those depths though. The drag and friction on the rope would be prohibitive. Microtraxion is the most likely product that would work for what you want, but the mechanism that holds the one way capture teeth open is pretty small to be used at those depths and to dis-engage mid dive if it were to get bumped from free flow mode to capture mode. A lanyard from the weight belt to the device would be the easiest for what you are saying though and could allow retrieval of the diver in a shallow water blackout if the one way action was already engaged. Good luck finding something that will work for what you are trying. BTW are you talking sled no limits type diving!

Hey DrApnea!

This device would only be used in constant-ballast dives, not sled ones because with sled ones the diver is normally hooked up to the sled, and the safety systems there are completely different.

The way constant-ballast competitive freedives currently work, in terms of safety, is a counter-ballast system. There's the dive line on one side with some weight (usually 10-20 kilos) to keep the line taut, and a bunch of weight on the other end of the dive line (around 40-50 kilos). The line goes across a rig, with a braking system in between. The dive line can be set to any depth (assuming the line is long enough), and then the brake is engaged. The dive line has a plate at the bottom, which is around 12 inches in diameter. The diver is hooked on to the line using a large carabiner. The carabiner attaches to a lanyard, which is attached to some part on the diver (weight belt/arm/leg). For example: divestock.com/breatheology-…. In the event the diver blacks out at depth (we have safety divers, but they only go to 25M-30M usually, so they're not very useful in a deep blackout situation), he will sink to the bottom of the dive line, where a plate will catch the carabiner. While the diver is sinking, someone on the surface will release the brake, and simple physics (weight on one side being much heavier than the other side) will bring the diver up.

The problem with this system is if the diver blacks out at around 40-50M, on say a 100M dive. He gets down to 100M, turns back around, comes back up to 40-50M, starts having trouble, and blacks out.. the counter ballast will be activated, but the diver is already sinking down because he's negatively buoyant. The diver could sink back down to 80-90M before the plate catches his carabiner and starts bringing him back up, which can cause quite a bit of injury to him. If we had some way of locking the diver in place, so that he wouldn't sink back down once he blacks out, it minimizes the amount of injury greatly. The problem is obviously that if there's a lot of friction caused by this device on the line, the diver has to swim with that much extra force, which obviously uses up extra oxygen/generate extra co2 etc in order to counter-act it, which makes the safety system more dangerous than anything (since it'll end up causing even more blackouts).

I'm looking into the micro Traxion right now. One thing I forgot to mention is that the line that this will be attached to will always be held taut (because of the weight at the bottom), which I think makes this slightly easier.

If the device can be attached without feeding one end of the line to it (I think the word I'm looking for is midline), that'd be very useful. But it's not a requirement.

Let me know what you guys think!

I think the way you described it a microtraxion will work. BTW it is designed to be put on the rope at any point (ie midline). Engage the capture teeth at any point on the deep point turn around or during the ascent and if the diver stop it will not allow them to sink below their high point (other than the lanyard length). It will work with ropes 8-11mm diameter per Petzl guidelines. Pulling the ascent rope upward will pull the diver with the engaged device upward as well. If the system is tight, the device should have minimal friction on the rope but will likely be a little bit more than your carabiner lanyard setup. You can pick one up for under $100 new and replace clip it at the carabiner location in your current setup. Not sure how durable it will be with saltwater though. I'd say buy one and give it a try, play with the mechanism, see if water drag is too much, and if it all works at shallower depths decide if the benefits outweigh the risks. Other freedivers will appreciate your testing and feedback for what could be a safer way to dive deep. Also ensure you have a way to remove yourself from the system (like the velcro strap in the link you posted or by removing the weight belt) should it get stuck for any odd/unforeseen reason. Let us know how it goes.

The Micro and Mini Traxion open up, and "wrap" onto the rope, so you don't need to feed an end into them. They can be secured on a line that is fixed at both ends.

In theory, they migh work in your application, but you'd need to test them out and see if the theory bears any resemblance to practice.

The are pretty effortless in moving along the rope when I climb with them, but I don't know how that would translate to diving. And as mentioned above, the locking mechanism that changes thme from locked open (slide up and down) to closed (only slide up, not down) is kind of small. It might be hard to engage in the dark under water.

Yep the Petzl Micro traction is your best bet especially since you are not going to be shock loading it at all or in any awkward way. No need to look any further. You have to use rope for it to work and if it's too thick like maybe 12mm then you will have issues closing the device and will have too much friction etc... Be safe!

Matt