Can 2 single ropes be used as doubles/twins?

As doubles, yes. But not as twins.

I'd do whatever the rope was rated for. Falling on two singles at once isn't going to stretch as intended.

Eli Buzzell wrote: I'd do whatever the rope was rated for. Falling on two singles at once isn't going to stretch as intended.

Agree with using what the rope is rated for.

However for doubles (not twins) the rope will "stretch as intended" if all the force of a fall is taken on one rope rather than shared between the two. That is always true before the second clip and may often be the case higher up, especially if the highest clip on one rope is a long way from the highest clip on the other.

I always thought double and twin is the same. Aren't the BD skinny ropes all rated as half and double? If so I would guess you could use one as a half rope paired with a single, but it seems weird to me. You definitely cannot use it as a double with a single though, that generates too much force on a fall. Easy solution is to just use it as a tag line.

For those that don't know the difference:

Double ropes (aka half): Each piece of protection only gets clipped with one rope (pieces off to the left get clipped with the red rope, pieces off to the right get clipped with the blue rope as an example).  

Twin ropes: Every piece of protection gets BOTH ropes clipped through it.

Nick Niebuhr wrote: I always thought double and twin is the same. 

No they are most definitely not.

Nick Niebuhr wrote: I always thought double and twin is the same. 

Doubles and halves are the same. Doubles and twins are not.

FrankPS wrote:

Doubles and halves are the same. Doubles and twins are not.

There's actually no such thing as double. It's a generic term used to describe climbing with 2 ropes i.e. double rope technique. It's a useful term to google for anyone needing to get up to speed on the various practices, but UIAA only recognizes twin and half in addition to single.

Sam Skovgaard wrote: For those that don't know the difference:

Double ropes (aka half): Each piece of protection only gets clipped with one rope (pieces off to the left get clipped woth the red rope, pieces off to the right get clipped with the blue rope as a ln example).  

Twin ropes: Every piece of protection gets BOTH ropes clipped through it.  

Red is always on the right. Unless you're a communist.

Types of double ropes:

• twin ropes
• half ropes

• isosceles
• scalene

YDGD! 

When I first started clinbing, the Scottish climbers I met were using a 11mm single with a 9mm half and climbing double rope style. They said it was the sharp rock where they lived that made them want a little extra cut protection. We also had an 11 and a 9 but the 9 was just a rap rope. Came to find out double rope style sometimes was the way forward for winding routes.

Beal has some triple rated ropes if you truly desire https://sport.beal-planet.com/index.php?id_product=1587&controller=product&id_lang=1
joker 9.1
I was using someone else’s 8.5 operas triple rated ice climbing last weekend 

i shore wrote:

Agree with using what the rope is rated for.

However for doubles (not twins) the rope will "stretch as intended" if all the force of a fall is taken on one rope rather than shared between the two. That is always true before the second clip and may often be the case higher up, especially if the highest clip on one rope is a long way from the highest clip on the other.

Thinking some more about this it MAY be OK to use differently rated ropes as half ropes (I certainly used to do so), but I'm not knowledgeable enough and am aware that that seems to ignore the UIAA single rope rating. Hopefully someone else will give a properly informed  opinion. Presumably a main reason for not using a single rated rope as a half rope is that, if the force of a leader fall is shared between two ropes, the impact might be too high (particularly if BOTH ropes were so rated, ie NOT as in the OP). Here are some further musings.

 As one gets higher up the pitch any falls are LIKELY to be of lower impact force since there is more rope in the system compared to the length of any fall (ie lower fall factor) so there will be increasingly less impact force if the force of fall is shared between two ropes and thus less importance if one rope is only rated as a single. Of course this may not be the case if runners fail, or if the load of a fall is shared between both ropes near the start of the pitch, or if all runners fail and there is maximum impact force. It would presumably usually be best to clip the true half rope first, as the more rope out at the earliest clip of the "single" rope the lower the impact.

Some Sticht plates used to be made with a wide slot for an 11mm single rope and a narrower slot for a 9mm half rope, so presumably in the 1970s Salewa thought it safe to use that rope combination for a half rope system as envisaged in the OP. However modern tube devices are a "one size fits many ropes" design rather than fitting two specific sizes which might have an influence (possibly in reducing impact force). I believe the UIAA rating tests are quite demanding and don't allow any rope slippage, so using a plate/tube device could mean the OPs suggestion was safe, since slippage would reduce impact in a severe fall.

It has been said its harder to arrest a fall with two different diameter ropes in the hand, but I don't know the evidence for this.

"It would presumably usually be best to clip the true half rope first, as the more rope out at the earliest clip of the "single" rope the lower the impact."

This is assuming a half rope gives a softer catch than a single. They are rated using different body weights so are not directly comparable.

Dave Olsen wrote: "It would presumably usually be best to clip the true half rope first, as the more rope out at the earliest clip of the "single" rope the lower the impact."

This is assuming a half rope gives a softer catch than a single. They are rated using different body weights so are not directly comparable.

Thanks. I seem to remember reading that the half rope UIAA ratings were a sort of compromise as they assume the load is shared between the ropes, which is certainly not always true. Also manufacturers may not always test their ropes for multiple uses. If a single rope  has a UIAA impact force of 8.5kN (UIAA max 12kN, 80 kg load), eg Mammut Galaxy, could one extrapolate that it would be below the 8kN maximum impact force of a half rope rated using 55kg?

The OP says they would be buying a new single so, as others have said, the obvious answer is to get a rope rated as single and half. 

After taking a lead fall on the first bolt with half ropes both clipped to the draw, I found it painful enough I don't clip like that anymore until I am higher on the pitch.

rocknice2 wrote:

Red is always on the right. Unless you're a communist.

Doesn’t red come first in the American flag? 

Dave Olsen wrote: After taking a lead fall on the first bolt with half ropes both clipped to the draw, I found it painful enough I don't clip like that anymore until I am higher on the pitch.

Good point. That was using the half ropes as twins at the first bolt (for which they weren't rated).

Even for rated half ropes I suppose it follows that low on the pitch a fall could be painful if the top clips on both half ropes are at roughly the same height, eg in parallel cracks. This would be almost equivalent to using them as twin ropes in relation to the impact on the leader (but not on the protection).

Here's an example of using the doubles incorrectly from the technical standpoint (increasing the impact force on the pro by being clipped as twins.) I also screwed myself strategically. The main reason I took doubles in the first place was in the hope that I could hang a runner over that horn up right and clip the second rope to it, but the directional pull because that cord was through the lower gear pulled the sling off. So things got serious, after a thin wire at the start of the seam that's it until you're all the way across to a good crack you can't see. Stoopid me.