Page 236 - Buck Tilton - Outward Bound Ropes, Knots, and Hitches 2 ed.

Tighten both overhand knots and draw them
together slowly by pulling on the standing parts

of both ropes.

Double Fisherman’s Knot

ONE OF THE SAFEST, MOST SECURE KNOTS FOR

JOINING TWO ROPES OF SIMILAR DIAMETER

As the name implies, the double fisherman’s knot extends
the fisherman’s knot (see page 88), joining two ropes or

lines of similar size in an extremely secure knot. In the
double fisherman’s, two double overhand knots jam against

each other when pressure is applied. It is an excellent
choice when using synthetic cordage, including fishing line.

It works in natural fiber cordage, of course, but it can
become extremely difficult to untie from anything other

than synthetics.