physics of Half rope method

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Francis

Trad climber
San Francisco
Topic Author's Original Post - Apr 12, 2009 - 09:33am PT
Happy Easter,

I have been obsessing on getting info about double ropes (aka half ropes not twin ropes). I get the reasons to use them and practiced it this last week using my two single ropes which are about 9.8. One is older than the other and is ready to be replaced...

Which leads me to questions about the diameter of half ropes and the logic or physics behind the ratings and fall safety of them. I probably am not going to articulate my question precisely but will try to.

Basically, it centers on why an 8ish rope is acceptable for half ropes. If and when you fall, are you still not falling on one rope, over a single edge? Does the physics of a fall change when you are using the Double rope technique? On your first piece, I am assuming it would be exactly the same as with a single rope as you have only one rope through one piece. If this is the case, then why would you be ok with having less of a fall rating?

Thanks climbing scientists!
Brutus of Wyde

climber
Old Climbers' Home, Oakland CA
Apr 12, 2009 - 09:45am PT
Here is a good place to start:

http://www.tradgirl.com/climbing_faq/advanced.htm#doubles

What I take away from this discussion is that half ropes have their place, and a leader always has the option of clipping both halves into a single, bomber, piece of pro (using separate carabiners) if facing long runouts, or the potential of death if a single-clipped strand would fail (such as your "first piece" scenario). Load limiters (such as Yates Screamers) also have their place in my toolbox of half-rope tricks.

You may take something else entirely from reading it, so I suggest a first-hand look.

Hope this helps.

Brutus
WBraun

climber
Apr 12, 2009 - 09:45am PT
Two 9.8 mm ropes are monsters. By the time you get to the end of a long pitch those ropes will pull you off.

I climb on a single 9.2 mm rope now.

Before that for over 10 years I climbed on a single 8.8 mm.
roy

Social climber
New Zealand -> Santa Barbara
Apr 12, 2009 - 09:56am PT
Hi,

My take as a double roping sometimes climbing engineer/scientist...

It's a trade-off. The fall on an individual rope is probably slightly riskier, but breaking a rope is very rare. Cutting the rope by running it over a sharp edge might happen but in that case you have a second rope waiting to catch your now somewhat slowed fall. If you're a wuss like me and closely space your gear then both ropes will catch you (word of experience here) giving better gear load distribution than a single rope.

The other advantages are: double length rappels; lower drag on wandering routes; being closely protected while pulling up the other rope to clip; backup in case of a damaged rope. The main disadvantage is the greater potential for a cluster and the need for greater belay skills.

Cheers, Roy

Steve Grossman

Trad climber
Seattle, WA
Apr 12, 2009 - 11:02am PT
Worth noting is the elongation under load for skinnier ropes. If you are using the double ropes traditionally to be able to spread apart your protection points with minimal drag then factor in the increased length of falls due to individual rope stretch when only one side of the system is loaded.
tradmanclimbs

Ice climber
Pomfert VT
Apr 12, 2009 - 11:06am PT
Skinny doubble ropes make total sense for multi pitch ice climbing. they make no sense at all for single pitch climbing. I use them for multi pitch rock as well simply because I hate the idea of dragging arround a heavy tag line. I have gotten totally spoiled with the option for full length raps and retrete whenever I feel the need.

The system is a pain in the butt though. easy to cluster, hard to belay properly. Still better than dragging a tag line for most of whAT I climb. If I climbed a lot of splitter cracks I would lead on a single and trail a line off the back of my harness. Doubbles suck in splitters. twice as much rope to get jammed against your feet.

I would say in the 11 years that I have been climbing on doubbles that 85% of the falls were caught on a single line. The other 15% were on both strands running through a single biner. It is nice to be able to place 2 pieces and clip one to each rope for a sketchy move but I have never actually fallen when I have rigged it that way.

Its nice in theory to speculate that you can provide a better belay by keeping red short while the leader clips blue but in real life it dosen't work that way. A Real fall in that situation would most likly resuly in a fair ammount of rope slippage while the belayer juggles fingers trying to brake the right rope. In reale life practice the belayer is more likly to feed the wrong rope and short you on the one you are trying to clip. then once you do get clipped you stand a decent chance of getting short roped on the other strand when you start climbing again.
System works great on ice where you don't keep the leader as snug as with rock. For hard rock climbing it is much easier to feed a single for fast desperate clips. Shoot out that slac and then reel it in fast when you hear the gate snap or the leader grunts, CLIPPED! If I am on an multi pitch climb and useing the half ropes if I have a line of bolts I will inform my belayer and treat the half ropes as twins and just clip em both to each draw. This is the easiest way to enshuer that you will get a decent belay and not get short roped or dropped.

I have concluded that doubbles are a PITA but I am a big chicken and I like the extra rope for retrete. I also like the rudundancy for cut protection when climbing in sharp nasty places. The price for being a chicken is that I must endure the doubble rope system on multi pitch climbs. If you are NOT a chicken then do yourself a HUGE favor and don't bother ;)

There are a few traverseing climbs arround where the doubbles really make it safe for your 2nd which is nice and a few where the doubbles really do help with the rope drag.

ec

climber
ca
Apr 12, 2009 - 11:35am PT
'practice' using two single ropes as doubles could lead to death as the impact force would most likely exceed what your body/pro could withstand. You might as well fall onto a static rope.
 ec
Brandon Lampley

Mountain climber
Boulder, CO
Apr 12, 2009 - 01:17pm PT
ec, why?

You're taking a fall on the single rope just like you would otherwise. Black Canyon climbers sometimes climb with 9.2 singles using double rope technique.

Now using 9.8's like twins would be NUTS! and I assume that's what you mean.
Tomcat

Trad climber
Chatham N.H.
Apr 12, 2009 - 01:27pm PT
I have clipped both to a single piece before I knew better.This can increase the load on the piece and stress on your body.

I love doubles and have climbed that way for 25 years.

The test weight for the half rope fall is lighter than a single rope weight,but similar to what I weigh.
ec

climber
ca
Apr 12, 2009 - 01:36pm PT
Brandon,
Yes, that's what I meant and this does happen quite often (clipping both ropes to that same piece)...the ropes aren't always alternated; that's when they become one BIG rope.
 ec
tradmanclimbs

Ice climber
Pomfert VT
Apr 12, 2009 - 01:48pm PT
It is perfectly fine to clip both strands of 1/2 ropes to a single piece of gear provideing that the gear is bomber and that you do not have the ropes widely seperated before or after that piece. If you plan on sepertaing the ropes dramaticly it is best to keep them seperate for the whole pitch.

The idea that your ropes will melt in half if both 1/2 ropes are clipped to a single draw or that the fall will be dramaticly harder is just a myth. Falls on 2 strands of half rope running through the same piece of gear feel just as soft and cushy as falls on a single rope. That being said you would be nuts not to take advantage of splitting the ropes if the gear is at all delicate. Additionaly if you had the ropes split by a large distance and twisted them arround each other and clipped them both to the same biner you could create a situation where you see some sheath melting. You would have to try really hard to create that type of situation. I have tryed pretty hard over the years and never managed to melt any sheaths. As long as the rope runs relativly straight and are relativle close to each other you can fall all day on them and it won't matter one tiny little bit that both strands are clipped to the same draw. I have tested this very thouroghly. I believe it was called Hang doggin BITD ;)

Contrary to pop belief the load placed on a single piece of gear clipped to a single strand of 1/2 rope is greater than the same fall on a single rope. (single rope has more material to absorbe energy than 1/2 rope) Where the 1/2 ropes come into plaY with sketch geAR situations is when you place 2 pieces of gear at roughly the same height and clip each seperatly to its own rope. This I believe does increase your safety dramaticly.
Ghost

climber
A long way from where I started
Apr 12, 2009 - 01:59pm PT
Which leads me to questions about the diameter of half ropes and the logic or physics behind the ratings and fall safety of them

No big mystery here. Falling on just one half rope is fine Ė you just canít do it as many times as you can on a single rope. ďFall ratingĒ is a measure of how many major (almost factor 2) falls a rope will hold before it breaks. In the real world, you can fall all day on one of your half ropes. Rope technology has evolved along with everything else, and ropes have become lighter and their diameter has decreased for the same strength.

And rather than having to choose between single, double, and twin, you can now have it both ways. Petzl is selling a rope (in North America, at least) which it claims is acceptable for use as either, and although I donít know for sure, I expect other companies are as well. Petzlís Dragonfly is an 8.2 mm rope (availabe in both 60m and 70m lengths) rated for 6 UIAA falls. Donít know what the fall rating is when used as a twin is Ė probably over 20. Iíve been using them for two seasons now and have nothing but good things to say about them. We generally use them as twins, but if a pitch wanders we split them as doubles.

As to belaying and rope management, thatís just a matter of practice. Youíll suffer through a few clusterfuks in the beginning, but it soon becomes second nature.

Biggest drawback is weight Ė two skinny ropes are heavier than one fat rope, and create more drag -- and at the end of a long pitch, youíll feel the difference. On the other hand, cutting your rappels by half is pretty nice. And thereís always the fact that if one rope gets cut, youíre not gonna die (well, unless you're rappeling at the time).
tradmanclimbs

Ice climber
Pomfert VT
Apr 12, 2009 - 02:06pm PT
Gohst, All 1/2 ropes are rated as twins. Read the directions next time you buy a new set. They even have little pictures that show it is OK. what they don't want you to do is seperate the ropes by a several meters and then stuff them both back through the same biner as this could cause the ropes to rub against each other at diferent speeds durring a fall possibly causeing heat damage to the ropes.

The big deal with the new Petzle and Sterling ropes is that they are rated as Doubbles, Twins and SINGLE.
ec

climber
ca
Apr 12, 2009 - 02:22pm PT
tradmanclimbs,
...of course, I was referring to the first post of using two single ropes in this manner...much different results than using halfs or twins...

 ec
Ghost

climber
A long way from where I started
Apr 12, 2009 - 02:24pm PT
tradmanclimbs: My bad. That's what I meant to say (as evidenced by the six-fall rating).

I'll go back and correct my post.

Thanks
tradmanclimbs

Ice climber
Pomfert VT
Apr 12, 2009 - 02:55pm PT
No worries... Its good to bring this stuff up as there seems to be a bit of myth associated with the doubble rope system. One of the biggest myths is that single strand of 1/2 rope has a lower impact force than a normal single rope. According to Sterling ropes this is NOT TRUE. A single rope has a lower impact force than a 1/2 rope because there is more material in the single rope to absorb energy. The skinny 1/2 rope can not dissapate as much energy and therfore transfers that energy to the pro. belay device and falling climber.
Tomcat

Trad climber
Chatham N.H.
Apr 12, 2009 - 03:20pm PT
The impact forces are similar.The melting is a myth.You don't clip them both to one piece because it increases the impact force felt by both the climber and the piece.That's not a myth.
Ghost

climber
A long way from where I started
Apr 12, 2009 - 03:24pm PT
Falls on 2 strands of half rope running through the same piece of gear feel just as soft and cushy as falls on a single rope

As someone who took repeated 50-footers onto a pair of half ropes running as twins (I had to do it. My country's future was at stake. Just ask Tami) (Well, that and there was a fairly large paycheck involved) I can confirm that you're not gonna die if you do this. I would say it was higher impact than a similar fall on a fat single, but I didn't get broken in half or anything.
Tomcat

Trad climber
Chatham N.H.
Apr 12, 2009 - 03:37pm PT
Right,and since the impact force is higher,and the protection experiences twice the impact force,it's not adviseable to clip them both.Most of the time it's not an issue because people tend to use doubles,or halfs,as intended,and split them,so what actually takes place is imperfect equalization,even when you get wiggy and clip them both to that piece at the crux.
Francis

Trad climber
San Francisco
Topic Author's Reply - Apr 12, 2009 - 07:10pm PT
Cool all very informative, thank you

...I just went on to the Uiaa sight and consulted their drop tests... they have them in written form and in picture form.

I must have a thick scull because I still cannot figure out why they would drop a lighter weight for the half ropes. You know I am going to the source and email them and see if I can get an answer from the horses mouth.

I will let you all know if I find anything of interest.

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