An emergency knot, the jury mast knot can be used to support a jury-rigged mast on a dismasted sailboat.
A. & B. Begin by making three underhand loops, each going under the one before.
C. Following the arrows, pull the inner bights of the outer loops to the side while extending the upper bight of the inner loop to form the knot.
D. Tighten the knot. Pull the rope ends aside.
E. Seize rope ends to the side loops. Temporarily screw or nail wood blocks to the jury mast under the knot to keep the knot from slipping down the mast.
You can support the jury mast knot by bending the stays and shrouds to the three loops with double sheet bends.
Original materials used with thanks to Irene Rodriguez and John Bennett