Single vs. Half Rope
The first distinction I want to make clear is between single and half ropes. Then, later in the article, I clear up the differences between half and twin ropes.
Single Ropes
Single ropes are the simplest and the most common. When you climb with a single rope, you clip all your pieces of gear (whether on a bolted sport climb or a trad climb) into one rope.
Belaying with a single rope is also simple. You can load it into a “single barrel” belay device, like a Petzl Grigri. Or into one of the two slots in a “double-barreled” tube-style device, like the Black Diamond ATC Guide.
For rappelling, you rig the rap at the halfway mark on the rope and rappel on two strands for half the length of the rope, which is most commonly between 30 to 35 meters.
Half Ropes
On the other hand, half ropes are slightly more complicated. When you climb with half ropes, you tie into each rope on either side of your belay loop. Then, when you climb, you clip the half ropes individually into different pieces.
Normally, you clip the rope on the left side of your belay loop to pieces of protection on the left side of your body. Then, the gear you place on the right side of your body is clipped with the other rope on the right side of your belay loop.
When you do this, the ropes should be clipped in alternating order–that way, there is no one section of the route where only one rope is clipped.
Belaying with half ropes requires a double-barrel tube-style device. Then for rappeling, both half ropes can be tied together with a flat overhand knot (or a double fisherman’s knot) so that you can rappel the full length of the two ropes instead of rappelling half of the rope.
Half vs. Twin Ropes
When compared to a half rope system, twin ropes are similar but still different. Like a half rope system, when you climb with twin ropes, you tie into and climb with two ropes.
Here’s the main difference: unlike half ropes, with twin ropes, you must clip every piece of protection with both ropes. That’s because twin ropes are not designed to be used individually.
For belaying, you have to use belay devices that can accommodate two ropes. In the case of twin skinny ropes, it may be advantageous to belay with a belay device designed for skinnier ropes, like the Black Diamond ATC Alpine Guide.
Rappelling with twin ropes is similar to a half rope system. You tie the two twin ropes together to rappel the full length of the two ropes.
However, it is important to mention that the skinny diameter makes rappelling on twin ropes significantly faster (this dynamic is also true for half-rope systems). Therefore, I recommend rappeling with a third-hand backup, like always.
Climbing Scenarios
In most rock climbing scenarios, a single rope is all that you need. For example, I have a selection of single ropes (a skinny 60-meter, a skinny 70-meter, and a thick 60-meter for top roping) that I use for different scenarios.
However, as you get into more niche objectives, you may need to explore the capabilities of twin and half ropes. Below I will share some common climbing scenarios for each type of rope.
Single Rope Climbing Scenarios
Top-rope climbing
A thicker single rope is ideal for setting up top ropes. A thicker rope can withstand the wear and tear that comes with top roping. And in a top rope setting, you are not normally concerned about weight savings.
Single-pitch sport climbing
If you enjoy single-pitch sport climbing, a single rope is all you need. When compared to top roping, thinner and lighter single ropes are preferred for sport climbs because they can be easier to manage and clip. However, if your typical approach is short, and you don’t mind the extra weight, a thicker single rope for sport climbing will last longer.
