Double Fisherman's Knot for Climbers: How to Tie It and When to Use It

What the knot is

A double fisherman's knot is formed by tying a double overhand wrap (sometimes called a double barrel) with each rope end around the other rope. Each wrap is a small stopper knot, and the two stoppers jam against each other when the ropes are pulled in opposite directions. The result is a symmetrical, compact knot that holds well on cord and rope.

Its strength comes from the way the two halves lock together. That also explains why it tightens down hard after loading and can be a struggle to undo. When you need a loop that will stay closed through lots of use, that is a feature. When you need a knot you can untie easily, it is a drawback.

How to tie it

Lay the two rope ends side by side, pointing in opposite directions with a generous overlap. With one end, wrap it twice around the other rope and tuck the end back through the two wraps, forming a double overhand knot. Pull it snug. Do the same with the other end, wrapping around the first rope, again with two wraps and a tuck.

Pull on the two standing ropes so that the two knots slide toward each other and meet. Dress them so the wraps are neat and parallel, with no crossings. The finished knot should look like two barrels side by side, with tails sticking out of each end. Leave tails long enough to inspect, typically a few inches or more depending on the cord.

Where climbers use it

The most common use is tying cord into a loop for friction hitches like a prusik or an autoblock. A closed loop of cord with a neat double fisherman's knot is a standard piece of kit for rappelling and self-rescue. Climbers also use it to make cordelette-style anchor slings from accessory cord.

Some climbers also use it to join two ropes of similar diameter for a long rappel, since it is compact and less likely to get stuck than some bulkier knots. Others prefer an offset knot like the flat overhand, for the same job. Which knot suits you depends on training and local convention, so follow the guidance of your instructor.

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Strength and limits

The knot reduces the strength of a rope or cord, as all knots do. Do not assume the full rated strength of the cord applies after a knot is tied. Manufacturers and testing bodies publish information about how knots affect rope strength, and your instructor can point you to current guidance.

Another limit is wear. A double fisherman's knot in a loop of cord that is used repeatedly for friction hitches will glaze and stiffen. Inspect the knot for fuzzing, hard spots, discoloration and cuts, and retire any loop that looks suspect. Cord is cheap compared with the consequences of a failure.

Inspecting and dressing

After tying, check that each half of the knot has the correct number of wraps, that the wraps lie side by side without crossing, and that the tails are on the outside of the knot. Look at both sides. A mirror-image of the knot on the back is a sign you tied it correctly.

Cinch the knot hard before using it, tugging on all four strands. A knot that shifts or creeps when tightened was not dressed properly. Retie it. A knot that looks neat on the table might behave differently once it is loaded, so test it at the ground before trusting it overhead.

Alternatives and practice

There are other ways to close a loop of cord, including a flat overhand bend, a triple fisherman's knot for slippery or thin cord, and sewn loops sold by gear makers. Each has trade-offs, mostly about size, strength and how easy the knot is to inspect or untie. Your course material will often state which to use.

Practice the knot on a length of waste cord until you can produce it consistently. Then ask an instructor or experienced partner to check it. Learning rope work in person, with gear that matches what you will use, is the dependable route.

Care, inspection and retirement

Any knot that has been loaded repeatedly deserves a close look. The double fisherman's knot can become very tight and difficult to inspect after hard use, and the cord inside it may be crushed or glazed. If you cannot see all the wraps clearly, or the knot will not loosen at all, consider cutting the loop and replacing it with a fresh one.

Store cord loops out of sun and away from chemicals such as fuel, solvents or battery acid, which can damage nylon. Note when you bought or tied each loop, and replace them on a regular schedule or whenever they look worn. Your cord manufacturer's guidance is the best source on service life.