Why Two Ropes?

Hi everyone, I’ve been getting into trad climbing as of late, and I’ve noticed (particularly on multi pitches) that many groups will use two ropes to climb with. I’m just curious as to why, and if I should be doing the same? Thanks!

I assume you mean climbing with paired lead ropes in the 7-9MM range for trad or multi-pitch bolted stuff. Yes they are very functional. 

For long routes, particularly something with a large commitment like, a 10+ pitch-long route you're doing in a long day or something in a true mountain setting (CO Rockies, Sierra, Wind River Range), having two ropes in one's possession becomes important for descending or for a contingency retreat. (This is true with OR without bolt anchor stations which big alpine routes will NOT have in which case you're leaving gear to back off the thing.) Also, there is an argument to be made for having two 60-70 meter ropes instead of one 80M or even a 100M single rope because the former better allows un-F*&ing yourself if say, a rope gets stuck on rappel or if a rope gets damaged or if you need no-kidding to do 60 or 70 meter rappels. (The limits of one long rope is an entire separate discussion. Lately, people seem prone to want one cord over two which is often unwise.) Paired ropes are also used in snow/ice conditions for the reasons stated here and because the dry versions seem better at not absorbing water than fatties. With paired skinny ropes it's also defensibly sane to climb something tall with a party of 3 because the the 2nd and 3rd climber can follow pitches simultaneously. This is the only way I would consider multi-pitch climbing with 3 people; otherwise you will go WAY too slow. (That practice is yet another separate discussion; short version is, you probably only want to climb with 3 people on two ropes for easy-ish climbing with solid anchors and only with a "half-rope" or multi-rated half/twin rope NOT a strict pure "twin" rope. My preference.) The alternative to paired ropes is either: 1.) 2 fat lead ropes with one being trailed or carried 2.) 1 fat lead rope plus a thin static line for rigging rappels. Generally, paired ropes are lighter than option #1 and weigh no more than option #2. 

Caution: If you're going to explore paired ropes, read and educate yourself to understand the different types and use-cases. The basic primer below is NOT enough information by itself: (These are the rope type symbols on the package and rope ends which dictate the technique used and rope's UIAA certification by type.)

Left: The standard single 

Center: The "half-rope" (Single strands are clipped in L/R alternation. These are very good for mitigating drag on wandering pitches.)

Right: The "twin rope" (Both strands are clipped in in tandem to EVERY lead protection point and one strand must NOT arrest a fall - ever.)

Multi-rated: Paired ropes may be "half" OR "twin" or both of these simultaneously. There are also triple-rated cords. Multi-rated means that the rope was test-certified in 2 or all 3 modes of use. These are not necessarily more useful than say, a strict half-rope but they are commonly seen nowadays. MOST not all, paired skinny ropes you will find are either dual-rated or triple-rated today. Triple-rated are usually fatter at 8.9mm to 9.1mm while duals are 7.5mm to 8.5mm - approximately. A dual-rated rope IMO is better for trad because that type tends to have lower impact force in test than triple-rated ropes; they're also the lightest. Beal ropes are particularly good IMO. The Beal Cobra 8.6 has been around for 30 years and still very good.

Lastly, it's worth pointing out that using paired ropes is a somewhat more advanced practice. It should involve a belay device that's specifically made a little smaller for skinny ropes and it requires some getting used to for both partners. (Forget Grigris altogether.) The probability of making big rope spaghetti at the belay is high when you are learning.

Again, look it up and read. I recommend owning the current PAPER edition of Freedom of the Hills as a basic textbook. You should also read anything by Andy Kirkpatrick. Defer to either of these over You Tube IMO.

Best. 

PS: This is all just 30-year-experience impressions and my own preference. Read for yourself - and not just on this site for God's sake. Bad information is readily available too.

Please read this entire site:
https://people.bath.ac.uk/dac33/high/

It will answer this particular question and many many others you have not thought of yet.