If you’re at all like me, at some point you’ll go down the dark rabbit hole of watching rock climbing videos ad nauseam on YouTube. During this voyage, you’ll cross a high degree of alpine, ice, and British rock climbing videos. Looking closely, you may notice that in many videos, the climbers are using two ropes. Some so skinny they resemble dental floss …

So why would a rock climber sometimes use two ropes?

Here we’ll discuss both twin-ropes and half-ropes. The history of their use and where this technique is headed now.

Half rope twin rope markings metolius
Image courtesy of Metolius. See the full rope instructions here.

Twin ropes

When shopping for ropes, twin ropes can be identified by two overlapping circles—a symbol that resembles a simple Venn diagram. Typically, only seven to eight millimeters in diameter, twin ropes are very skinny. With twin ropes, a climber ties into two separate cords, one on each side of their belay loop. As they climb, they clip both ropes into the same piece.

Why use two climbing ropes?

Twin ropes add a couple of benefits over climbing with just a regular, fat single rope.

First off, twin ropes allow climbers to rappel the full length of their rope. If you climb on a single sixty-meter rope, you are only able to rappel thirty meters. With twin ropes, however, you’ll be able to rappel the full sixty meters. If you’re hiking deep into the alpine, carrying two skinny ropes weighs less than carrying two single ropes.

Additionally, if there is a risk of the rope being damaged from extremely sharp rock or ice climbing (with all those medieval tools attached to you) then there is the benefit of the redundancy provided by using two ropes. Furthermore, these skinny twin ropes are uber stretchy which reduces the amount of force placed on your gear during a fall.

This sounds great! Why not always rock climb with twin ropes?

Well, there are a few reasons …

1. Tangles

As many rock climbers have experienced with just one climbing rope, rope management isn’t always as easy as you would expect. Tangles and knots seem to appear out of nowhere when managing climbing rope and it is a pain to detangle a rope. Since skinnier ropes are more susceptible to getting tangled, having two skinny ropes to manage can be a strong lesson in patience.

2. Cost

In addition to having to buy two ropes despite being skinny, twin ropes still cost a pretty penny.

3. Rope drag

Pulling two 7 mm ropes through numerous carabiners, 50 meters up a long wandering route can add up to some pretty horrific rope drag.

4. Multi-pitch limited to 2 climbers

You can only rock climb with yourself and your partner. You cannot multi-pitch climb with a party of three, because the followers cannot tie in independently to single strands of twin ropes.

How to use twin ropes

Belaying with twin ropes is fairly straightforward. You need to use a belay device with two tubes for belaying, like an ATC. Belay devices that can only accept a single rope, like the ATC Sport or Petzl GriGri can not be used with twin ropes.

Giving and taking slack is exactly like belaying a single rope. However, you do need to make sure that your belay device is approved for use with skinny ropes. Some have a minimum diameter of 9mm meaning you won’t be able to safely belay with twin ropes. Devices like the Edelrid MegaJul do a much better job at catching falls. The assisted braking of these devices adds a higher likelihood that your dental-floss sized twin ropes won’t be ripped out of your hands when your partner falls.

ice climbing with twin ropes

Twin ropes are most commonly used when ice climbing. Sharp ice creates a risk of damaging rope so redundancy of the second rope is important. Climbs typically don’t meander much so rope drag is less of a concern. The routes are generally longer than your typical rock climbing pitch so the extra length is useful for belaying.

These days, outside of ice climbing, twin ropes are not used very often.

Related Post: 10 Best Climbing Ropes

How to use half ropes

Compared to twin ropes, half ropes are slightly more complicated …

Just like twin ropes, half ropes require climbing on two ropes. You still tie in with one rope on each side of your belay loop of your harness. But, contrary to twin ropes, half ropes are not clipped into the same piece of protection. They are clipped individually to different pieces.

A climber will clip the rope to the left of her belay loop into pieces placed on the left side of their body. Gear placed on the right side will be clipped with the right rope. Ideally, these ropes are clipped in an alternating fashion. There should not be a long section of a route where only one rope is clipped.

This is an extremely important distinction. Confusing which type of rope gets clipped, which way can be fatal.

To reiterate, half ropes are clipped independently from each other.

Half ropes generally have a diameter of 7.5 – 8.5mm (some as skinny at 7.1mm) and do not have the same strength of a single rope.

This begs the question; can a climber fall on a single half rope?

The answer is a very timid yes, quickly followed by a heavy NO.

Half ropes are not designed to take individual falls. While they are tested individually for strength, a 55-kg mass is used, not an 80-kg mass. If the rope can withstand five 1.7 factor falls (see here to read more about fall factors) with a 55kg mass, it is considered safe. Doing the same test with an 80-kilogram mass, most half ropes fail at one or two falls. This means there is potential that it could catch a climber, but you don’t want to be the one betting that it will. Do not fall on a single half rope!

The reason that half ropes can be tested with a smaller mass is that the theory behind half ropes is they will share the fall. While one-half rope will take the bulk of the fall, the second rope will absorb some of the force as well. By sharing this force between two ropes, they can be rated to a lower amount.

Related Post: Everything You Need to Know About Climbing Ropes

What is the point of half ropes then and how do they differ in application than twins?

1. Rope drag

By clipping alternatively, the rope drag on wander-y routes can be significantly reduced. Instead of having a single rope or twin ropes zig-zagging across a route, clipping the left pieces with the left rope and right pieces with the right rope eliminates bends in the rope and therefore decreases rope drag.

2. Lower fall force

Because the ropes are clipped independently, but both share the fall force, the force on pieces placed is reduced. Questionable placements that may not hold to the entire load of a fall now can share some of that load-bearing with the gear holding the other half rope.

3. Rappel distance

Like twin ropes, you can rappel further with half ropes than if you brought one single rope.

4. Weight

They are light while still adding durability and redundancy by rock climbing on two ropes.

rock climbing with half ropes

Half ropes were appropriate on this wandering climbing which ended in a 55m rappel.

This sounds great! Why not always rock climb with half ropes?

I can personally attest to some of the downsides to using half ropes.

1. Belaying requires practice

A lot of practice! The learning curve on how to safely give slack on one rope while taking in slack on the other rope is not quick. A belay device like Edelrid’s MegaJul makes this significantly easier and safer and should be considered when belaying with half ropes.

2. Which side to clip?

Half ropes require a lot of thought. While some routes may be straightforward with which rope gets clipped to which piece, many are not so black and white. Zach Attack, a multi-pitch mixed climb in Hyalite Canyon, is a great example of this.

The first pitch is roughly seventy meters and starts heavily to the left, trends right, and then heads sharply back to the left. While I thought I was clipping properly down low, I quickly learned fifty meters up that I made a mistake by clipping my right rope too far left thirty meters before, and had to struggle through heinous rope drag through the final bit of the climb.

3. Highly elastic rope

Party of three? Maybe. Technically, it is ok if two climbers follow on independent strands of half ropes. However, the elongation of half ropes is significantly higher than single ropes. Early in my climbing career, I was following a steep ice climb in Hyalite when the mushroom I was on broke. Despite being twenty-five feet off the ground, with the stretch of the half rope I ended up hitting a ledge hard. While I was okay, it is a strong reminder to consider whether half ropes are appropriate for a climb if it is extremely ledge-y.

4. Durability

If there are sharp arêtes and your follower falls around a corner, it will not take nearly as much force to sever the rope as a typical single climbing rope.

5. Cost

Like twin ropes, half ropes are not cheap. And again, like twin ropes, you are stuck buying two ropes.

rock climbing half rope belay

Twice the number of ropes, twice as much time spent managing your ropes.

Considering what diameter half rope is used also matters. The skinniest half rope is 7.1mm, however, I wouldn’t use that on rock due to lower durability. An ice climb with a bit of rock would be great for such a rope, but on alpine granite climbs something closer to 8-8.5mm would provide more assurance of not getting cut and it would last longer.

Other considerations for twin and half ropes

1. Buy ropes of different colors

Nothing complicates rappelling or clipping strands independently like looking down and seeing a bunch of ropes that look the same.

2. 60 or 70-meter length?

Default towards the 60 meter half rope. Unlike single ropes, having more rope is not always helpful with half ropes. Generally, you won’t be climbing for the full seventy meters, and the twenty extra meters of rope is extra weight and extra time spent flaking and managing tangles.

3. Technology has progressed in the climbing rope world

Many half ropes are available as skinny seven-millimeter cords and still safe to clip independently. Many half ropes are now also rated as twin ropes. These ropes, called “double rated ropes,” give climbers the ability use different methods depending on the type of route they are climbing.

If doing a wander-y alpine route, clip the ropes independently; if doing a straightforward ice route, clip the ropes as twins. Double rated ropes are much more versatile than strictly rated twin or half ropes. Twin ropes were never very common in America but with the development of double rated ropes, twin ropes are fading into obscurity.

ice climbers with twin ropes

Which should I use? Twin rope or half rope?

Considering when to use these ropes as twins or halves is very route dependent. Rock climbing in the Verdon Gorge in Southern France is one example where climbing with twin ropes is easier. In the Verdon, many climbs start with a rappel into the gorge. Then long, straight pitches lead out of the Gorge.

However, in most cases, half ropes, (alternating which rope is clipped) is more beneficial. Climbing with half ropes rather than twin ropes has the benefits of reduced rope drag and better distribution of forces across more pieces of gear during a fall. A win-win choice for most climbing situations.

Rappelling

When rappelling I always recommend using a backup. But when it comes to twin ropes or half ropes this becomes even more important. The likelihood of losing control of the ropes is significantly higher with skinny ropes.

The first time I used the Beal Gully, a 7.3mm half rope, I rappelled without a backup. Breaking one of my own rules! It was a gripping rappel. And I felt out of control the entire time. The next three rappels after that, I added a prusik. It is worth the ten seconds to tie a prusik to be in control; you’ll still rappel plenty fast on skinny cords.

rock climbing rappel with two ropes

Guide for selecting your twin ropes and half ropes

1. Diameter and sheath percentage

Are you strictly ice climbing, where you can get away with skinnier cords? A higher sheath percentage equates to a more durable rope, which may or may not be necessary.

2. Dry treatment

Just like your single rope, if you’re going to be in the alpine or out ice climbing, get the dry treatment.

3. Length

Unless you’re looking at specific climbs needing longer ropes, sixty meters is more than enough for both half ropes and twin ropes.

4. Weight

Lighter does not always equal better. if you have to sacrifice durability and safety for a couple less ounces to climb with.

5. Color

Make sure the ropes are different colors or leading and rappelling will be annoying.

6. Rating

Is it just a twin rope, just a half rope, or is the rope double rated?

As always, consult a professional guide to learn the deep ins and outs for belaying with both twin and half ropes!


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