I often get the question from non-climbers “how do you get down and how do you get all your gear back after you’re done with a climb?”.
Short answer:
On a climb where you don’t top out you will usually find some sort of fixed anchor at the top of the climb. To get down you feed your rope through the anchor until half rope, then with stopper knots in both ends you rappel down both strands at the same time. When you reach the ground you untie the stopper knots and pull your rope back through the anchor leaving behind only the fixed anchor. Now, this method only works if you need to rappel a distance equal to or less than half the length of your rope. For distances greater than that you can tie two ropes together and now rappel twice the distance and still be able to get your rope back.
Then the question comes up, what knot is the best for tying two ropes together.
After some research on the internet and a few different knot books I have, I have found the four most common knots are the double figure 8 fallowed through, the double fisherman’s, the double overhand (European Death Knot) and the square fisherman’s knots. Each of these knots has their advantages and their drawbacks.
Double Figure-8 This knot, the usual way to tie rappel ropes together, is the strongest of the bunch and, if properly tied, will not come undone. It’s also easy to visually check to make sure it is properly tied. It’s usually not difficult to untie after being weighted. This is the best knot to tie ropes of unequal diameters, that is a thin rope and thick rope, together. The knot’s biggest disadvantage is its bulk, so the chances that it might jam in a crack while you’re pulling the rappel ropes are increased.
Double Fisherman’s Knot This is the traditional knot to tie two ropes together but has generally fallen out of favor for other knots. It can be difficult to check visually and is often difficult to untie after being weighted, particularly if the ropes are wet. This knot is best used for tying thin pieces of accessory cord like Spectra together for anchors or slinging nuts like Hexentrics.
Double Overhand Knot This knot, sometimes called the “European Death Knot,” has gained popularity and is often used to tie ropes together. It is the fastest and easiest of these four knots to tie and has the least bulk, which makes it less likely to snag and stick your rope. Do not use this knot with ropes of varying diameters, since at least one fatal accident has occurred from it coming untied. Alternatively you can tie a double figure-8 knot instead of the overhand knot, although testing at Black Diamond’s lab in Salt Lake City indicates that the double overhand is stronger than the double figure-8.
Square Fisherman’s Knot A lot of climbers like this knot because it’s easy to tie and the easiest of these four knots to untie. It’s basically just a square knot backed up with double fisherman’s knots on either side. If you use this knot, always use the backup knots or risk it coming untied. A square knot alone is never a good knot for rappelling or any other climbing purpose.
I also found this interesting article done by the Black Diamond Lab http://www.blackdiamondequipment.com/en-us/journal/climb/all/qc-lab-what-is-the-best-rappel-knot.
One knot you should never use to tie two ropes together is a double figure 8 where both tails come out the same end. Once weighted this knot can easily unwind itself untying the ropes and leaving you unanchored. At least one climber has died because of this knot while rappelling.
gjclimbing 
Posted on August 23, 2012
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