Essential Knots

Water Knot
Also known as a "ring bend" or a "retraced overhand." This is the preferred knot for webbing. It allows the flat material to lie without folding. It's symmetrical and strong, yet not very secure unless tightened carefully. Check water knots in webbing frequently, and be sure to leave at least an inch of "tail" after tightening. Such a knot works in rope as well, but it isn't as secure as the double fisherman's.

Double Fisherman's
Also known as a "grapevine" knot, this works graphically by having two knots block on each other: The result is a symmetrical double-X design, easy to inspect. It is the most secure way you can join two ropes or ends of cords for slings. But once loaded, it's hard to untie. Prusik cords tied with a double fisherman's will be more or less "welded" in place after a few uses. Rappel lines tied with this knot can be worked loose with a little effort once you're safely on the ground. Keep the X's lined up for symmetry. One half of the double fisherman's makes the best backup knot to use in conjunction with other climbing knots.

Clove Hitch
The beauty of this variation is that it allows easy adjustment without your having to dismantle the knot. When at a belay, for example, the leader who uses a clove hitch to fix his rope to the anchor carabiners can readily adjust his positioning so that he can belay most effectively. If he had tied a figure-8 on a bight, he would have a harder time adjusting and might be tempted to belay without the exact anchor length needed to do the best job.

The clove hitch is, however, very fickle. If it isn't cinched down tight, it can ride up the carabiner gate and open the 'biner. Not good. Note also how it loads the carabiner. If it is backwards, the strength of the carabiner will be compromised because it is being loaded out away from the "elbow" of the 'biner: Use doubled, opposed carabiners to eliminate this danger. The clove hitch works well to link several anchor points, but you'd still be wise to include a "hard knot" like a figure-8 or overhand as part of any anchor system using clove hitches.