Adjustable bridge length using Hitchclimber pulley

[Burnham]

I'm again facilitating at this year's USFS R6 climbing instructor workshop, this week in fact. Yesterday I saw this new-to-me method of deploying a Hitchclimber, providing instantly adjustable split tail bridge length.

The only downside I see right off the bat is the tight radius bend of the climb line through the harness attachment point...probably not ever going to cause a problem, but it really isn't right either.

Seems like I recall having seen a similar setup using a mickey mouse pulley sometime in the past, but I might be mistaken.

Pics.

 

[Old Monkey]

Its not really an adjustable bridge so much as a system for adjusting the distance to the friction hitch for switching ove from ascending to descending mode. Its interesting but I don't see using that. That bend is tight but not much tighter than a knot on a biner. The VT looks funny too.

 

[CurSedVoyce]

Good eye Darin.. It looks like she skipped a braid.
Interesting, but my next HC pulley is going to be right on my rope bridge for extra connection points.

 

[Treepreacher51]

I have seen that, but a Ropeman cammed, micro ascender was used in place of the prussik and wire gare beaner. As Darin said, not an adjustable bridge, but a neat and quick transition from hand over hand body thrust/ascent to working or descent.


Was that climber a guy or a gal? Pat?

 

[DMc]

You have a great job, Burnham. Nothing like young eager minds to keep you on your toes. The system you showed is actually best suited for using the Hitchclimber on lines with no eye splice. A termination knot located below the HC will not interfere with the hitch functions. I am not a splice guy but I have heard that when the configuration you showed is in the close-to-saddle position, the eye splice is being,or can be loaded very badly for its health.

Dave

 

[Brocky]

I've seen this called an O Rigging System because it forms a contiuous circle from the climber to the TIP. With a self tending friction hitch this system seems to complicate things unless you like the idea of having your hands below your hitch. Mostly knuckle dragging knot pushers (like myself) tend to use adjustable bridges.

To get a better bend radius a pulley can be added to the harness attchment carabiner. A larger pulley, like a prusik minder, needs to be used so that the spliced eye of the climb line can easily pulled through it if the line needs to be advanced.

The system I use has the friction hitch on the right side (as in the pictures) that is clipped to a 24 inch long double eye cord that goes through a pulley on the harness attachment carabiner that then is clipped to the climb line eye. A second friction hitch is tied on the 24 inch cord on the left side of the pulley. This hitch stops the climb line from rotating as it is pulled to hip thrust. To advance the climb line I just have to unclip the eye.

 

[canadianclimber]

Saw this on youtube. Never tried it. Similar, with a little more gear.

http://www.youtube.com/user/Tr33Climb3r#p/u/3/5IxODdIUiWo

 

[Burnham]

Its not really an adjustable bridge so much as a system for adjusting the distance to the friction hitch for switching over from ascending to descending mode. Its interesting but I don't see using that. That bend is tight but not much tighter than a knot on a biner. The VT looks funny too.

I would have thought that "a system for adjusting the distance to the friction hitch for switching over from ascending to descending mode" describes an "adjustable bridge". I guess not, so can you educate me in the difference?

 

[cory]

B, I'm surprised you mentioned the bend radius- isn't it identical to the radius in an eye splice or in a scaffold/fisherman's noose knot on a biner, which are both ubiquitous in the industry?

 

[Burnham]

It's also ubiquitous in the industry to consider a rope bend radius of less than 4:1 to be too tight for retaining full breaking strength of a rope....I don't know the answer to your question, but your points are well taken, Cory.

 

[Old Monkey]

In my mind a bridge is a rope or sling that goes from one side of your saddle to the other, not simply extending from a fixed point on your saddle to your friction hitch. I could be wrong.

 

[Burnham]

Ahhh...agreed, that's a term we use for that part of a saddle. But we also refer to the split tail (or hitch tail in a trad system) between the saddle attachment and the friction hitch itself as the bridge, as well. Confusing.

 

[Burnham]

You have a great job, Burnham. Nothing like young eager minds to keep you on your toes. The system you showed is actually best suited for using the Hitchclimber on lines with no eye splice. A termination knot located below the HC will not interfere with the hitch functions. I am not a splice guy but I have heard that when the configuration you showed is in the close-to-saddle position, the eye splice is being,or can be loaded very badly for its health.

Dave

Your point about the knot termination makes a lot of sense, David...and it was noted at the workshop by the person showing this arrangement that the system should not be shortend onto the bury of the splice.

 

[cory]

Yes, the 4:1 ratio seems to be fully ignored when it comes to one's lifeline. That always bothered me and I was forever messing around with thimbles and various knots which afforded a better bend radius. But eventually I gave in and joined the crowd and don't worry about it now, suscribing to the conventional wisdom that the poor bend radius is basically irrelevant to safety given the relatively small amount of weight the climbline holds.

 

[Brocky]

Maybe these should be called adjustable friction hitch bridges to tell them apart?

The bend radius on this system has the rope running through it while an eye is stationary on the carabiner which makes a difference.

 

[DMc]

Yes, the 4:1 ratio seems to be fully ignored when it comes to one's lifeline.

I am not positive that I am right but the 4:1 min. would be more applicable when there is movement at the point of bend. A choked off termination knot has many other forces in play besides just the bend ratio.

Dave

 

[Burnham]

Agreed.

 

[wiley_p]

Was that climber a guy or a gal? Pat?

 

[OTGBOSTON]

I got slammed for posting a pic of that setup a few years back...I believe Nate called it (paraphrasing) "fine for rec climbers, but not practical if you have to swith tie in points often"

 

[cory]

I am not positive that I am right but the 4:1 min. would be more applicable when there is movement at the point of bend. A choked off termination knot has many other forces in play besides just the bend ratio.

Dave

That is interesting to me, can you elaborate?

 

[DMc]

That is interesting to me, can you elaborate?

Strength of a termination is dependent on consistent and measurable characteristics such as fiber type, construction type and binding method. Just add up the numbers and you will know what you are dealing with. Knots have pretty well documented strength loss ratios as do eye splices. A small, tight Grizzly splice retains most of the rope's strength even on a carabiner.(?) (I put a question mark there because I have not seen proof of this.)
However, when you add movement, you introduce a cycles-to-failure component where the bend ratio is very important and harder to measure. Each bend, at a sharp angle, creates wear or fiber damage. So how many times did that one section of rope move across the pulley or biner? This is why block manufacturers are so adamant on open-angled bend ratios. Movement on a bridge ring is not only below the recommended ratio but quantifying the number of times the movement occurred is going to be more than difficult.

Dave

 

[Peter]

I had a true adjustable length bridge on my TreeMotion, using a Ropeman 2 as the adjuster.

Remove the original bridge, replace with long bridge (I had about 1.5 metres) and put Ropeman just behind one of the dee rings, with a biner through it.

Hope that makes sense, if not I can probably find a pic somewhere.

Stopped using that and the O rig setup as I just don't find them that useful for the type of climbing I do.

 

[Peter]

It's also ubiquitous in the industry to consider a rope bend radius of less than 4:1 to be too tight for retaining full breaking strength of a rope....I don't know the answer to your question, but your points are well taken, Cory.

A Petzl Ultragear pulley on the bridge biner could help eliminate bend radius issues.

 

[Brocky]

I' ve found that when using just the Petzl plastic sheave in this way the rope has a tendancy to slip dff due to the twisting of the rope. A micropulley works much better.

 

[Peter]

Did wonder about that, a micropulley obviously adds unwanted length to the system, but does the job perfectly.