What's the best knot for turning a piece of cord into a loop? The cord would then be used for a prusik so needs to be very secure and load bearing.
I believe the conventional way is to use a double (triple) fisherman's bend. This has the advantage of being and relatively compact. The main disadvantage is that it can be hard to undo if you need to.
Other options include the figure of 8 bend which is bulkier than the fisherman's but easier to untie.
You could also use a (double) sheet bend or even a reef knot but these definitely fall into the less secure category.
1Oh, I don't like the look of a sheet bend. A couple of meters up and it'll probably look worse!– user2766Jul 17, 2014 at 9:08
2Yes I wouldn't use it for climbing. If you want a loop to hang a bag from its ok though. Easy to tie and undo.– nivagJul 17, 2014 at 9:30
@nivag Great link Jul 17, 2014 at 14:41
3My Prussik loops are tied with a triple fishermen's bend, as is the loops of everyone I know, including the instructors on the Intermediate Snowcraft Course I attended a few years ago. As an aside, the instructor recommended the loose ends of the knot be tidied away with non-adhesive heat shrink tubing. Jul 18, 2014 at 2:36
1This answer could be improved by cutting the last paragraph. A reef knot is not a secure enough knot for this purpose.– user2169Aug 7, 2014 at 14:48
I use the (double) Fisherman's knot for such cases. It's easy to tie and has a clear and concise form (easy to check if done right). As already mentioned in nivag's answer, it can be hard to untie if it was heavily loaded.
One of its drawbacks is that it is not applicable for webbing as it is not possible to tighten it there to be stable. Here the waterman knot comes in handy.
Coming from a climbing and industrial rope access background, the double fisherman's is the recommended way to make a loop using rope/cord.
Undoing the knot was never part of the question, however under body weight loading even this shouldn't be too difficult.
The figure of eight would work equally as well, I'd use it more for joining ropes for long abseils where undoing it afterwards is essential. Once you've made your prussik loops though there should be little reason to alter them.
Stay away from the sheet bend, this is not really for climbing.
Reef knots again, not really for climbing. Use with caution and back them up with a stopper hitch to stop slippage.
Re the figure eight, it's important not to use the offset (flat) form as a bend, because it capsizes very easily and has been implicated in a number of accidents: user.xmission.com/~tmoyer/testing/EDK.html– user2169Aug 7, 2014 at 19:41
@BenCrowell To clarify, the Fig 8 knot I was referring to involves first of all tying a single fig 8 in one rope then threading the second rope though and around the knot in reverse, creating a very linear knot (similar to when you're tying in). This can't capsize and in the link you attached, fails when the rope breaks.– RogerBAug 8, 2014 at 15:05
Right, I just wanted to make sure that was clear to other people reading your answer.– user2169Aug 8, 2014 at 20:02
I alternate between the double fisherman's (which everyone has already talked about) and the flat overhand. Lately I've been leaning towards the flat overhand.
The benefit of the flat overhand is that it's much easier to tie, inspect, and (most importantly) untie after it's been loaded. When properly tied and dressed, the flat overhand has been shown to be more than adequate for joining two ropes together (or creating a loop) in climbing applications.
Being able to untie a loop can be very useful and provide more flexibility. For example, you can turn a long cordelette into bail gear during a descent, or use the cord for an application where it would otherwise be too short.
1The flat overhand is also known as an offset overhand or EDK (Euro death knot). I was going to suggest the same knot. I've been told to leave long tails, and to tighten each strand against each of the other strands on the opposite side.– user2169Jul 17, 2014 at 20:29
1I'm not a big fan of that alternative name because of the connotations it brings :). Agreed, dressing it well (pulling on each pair of strands) is key.– FelixJul 18, 2014 at 13:26
How about a Figure 8 Bend?
Easy to untie even under heavy load. We use them all the time in rock climbing.
1-1. A square knot isn't very secure, and its correct application isn't as a bend.– user2169Aug 7, 2014 at 19:46
1I just noticed this was for a prussik, which of critical, so I removed the square knot. Aug 8, 2014 at 19:59