Whatever knot you chose remember you must put the thicker rope through the anchor/rap ring. Especially if you simulrap.

There is a reason to thread the thicker rope. With two ropes of unequal diameter, the higher stretch of the thinner rope (together with the thinness) will typically cause it to run through the rappel device faster than the thick rope. The point of threading the thick rope is to allow the knot to jam up against the rap rings and so prevent unequal running of the strands.

If this happens with the thin rope threaded, then the knot, which is on the thick rope side, will be pulled down as the rappeller descends, with the result that the ends may be very uneven at the bottom. Without knots in the ends of the rope, uneven ends seem to be the primary cause of fatal rappelling accidents. So climbers who thread the thinner rope for the pulling advantages that method confers also have to be extra vigilent about unequal ends. One way around this is to stabilize the two strands at the anchor by clipping them together with a quickdraw for everyone but the last person down. The party below can manage the ropes in a fireman's belay for the last person, although the tug of war that might ensue could make it hard for them to descend...

It is also possible to rappel without the ends becoming uneven---the rappeller has to feed the rappel rope hand-over-hand into the device, rather than allowing the strands to slip through the brake hand.

Well it depends on the situation. If there is enough rope left I can simply relead the pitch.
...
But I guess the largest problem would be determining if there is enough rope left to reach the problem site

I don't think you've got a big enough difference. 10mm and 7.5mm and you'll see it plain as day.

If there is not enough rope left to do a normal free climb lead I can do a roped solo lead with two locking biners and a clove hitch. If both ends of the rope are still at the belay station I can ascend the line with cordlet tied in a prussic or slings with a climbheist. If there is not enough rope to relead the pitch normally, I can also use a prussic or GriGri to climb the rope in a roped solo mode as opposed to the double carabiner and clove hitch method (assuming the other end of the rope can be tied down and assuming the rope is still running through the rap ring).

But we are specifically talking about Dark Shadows, right?

What am I missing in these scenarios?

a) Could you explain why a roped solo lead requires less rope than a normal free climb lead??

c) If "both ends are at the belay station" and you have a partner, why would you ascend the lines with a prussik or klemheist? Why wouldn't you just run one (if one of the ropes is snagged off to the side and you're short on additional rope) or both ropes through your ATC or similar device (you haven't lost that or ditched it in favor of a gri-gri have you?) and have your partner give you a fireman's belay?

Knowledge of how to rope solo and ascend a fixed line, apparently.


Because for a belayed lead, the climber ties into the end of the rope and the belayer runs a bight of rope through his belay device. There has to be enough slack in the rope so that the rope will be able to run from the stuck point down to the belayer and back up to the stuck point.

When you rope solo, you anchor one end of the rope, tie into the middle of the rope, and move up your tie-in point as you ascend, so you can rope solo the route with very little slack in the rope.


To ascend a rope you use prusiks. A belay device is not necessary or useful, nor is a fireman's belay. There is no such thing as "up-rappelling."

Jay

Thanks for clarification.

Re. a) If I'm understanding right, you're proposing that he'd rope-solo the stuck end of the rope, just needing enough slack for the clove hitches and any backup knots?

I use a square knot backed up by a double fisherman, 9.8lead, and 6mm static tag for weigh and less friction when pulling.

So elegant, so simple, so... knotty. I've never used it for rapping (I just use it to secure my chalkbag belt), but with a double fisherman backup, I bet it's as good as anything else out there. The sharp bends that "weaken" it is the big argument against it, I gather, ...

So ... --what?!
So ill-suited to different-nature (size, stiffness, ...) ropes!
And backed up with Strangle knots, which are the component
halves of a Dlb.Fish./Grapevine.

Aside from poor performance w/mis-matched ropes, the Square
knot w/back-ups is much more bulky and difficult to pull over
a surface than the Offset knots previously cited. (And well
longer to tie/untie, though simple enough.)

It might be noted here that the back-up, Strangle knots in this
case are only as tight as one sets them; in contrast
to the simple Overhand back-up for the Offset Ring Bend (EDK),
which will be tensioned further by loading (if it is set properly
snug to the ORB body). Indeed, some might prefer the Thief
knot (Square form, but loaded on catercorner ends) precisely
so that in slippage it will bring the Strangle back-ups into some
tension. (But that doesn't help with flow over a surface.)

*kN*

I certainly agree about a square knot not being safe for ropes of different diameters. Sailors discovered this quite some time ago. In situations with differing ropes, there is another knot that is superior. But, I wouldn't use it for rappel. One of the dangers of the square knot is that, with ropes of differing stiffness, it can transfer into a girth hitch around one strand. Basically like a one wrap prussik. In fact, this transformation is where the other name of the square knot is derived from - the reef knot. It was used to reef sails (bundle them up for less area in the wind) because it could be shaken out by pulling on one strand. Not something I would trust without back-ups.
The EDK is much better suited for rappelling applications.

I stopped reading at "Sailors". Did I miss anything?

i understand the concept and theory behind this, but to be honest, i've never experienced it myself- and i regularly alternate which rope gets pulled, but i have never experienced noticeable rope creep with my two lines (9.8mm & 8.4mm). thats not to say it doesnt happen in other instances, i'm just posting an observation.