Knots by Grog say:
If you are asked to learn to tie the Sheepshank, please request your
Troop Leader to eliminate this knot and replace it with something safe
and useful, e.g., the Alpine Butterfly Loop is an excellent way of
creating a loop in the middle of a length of rope and can also be
safely used to shorten a rope.
So it sounds like you want an
There are several methods for tying it. We devised the method that is
used in the animation. It is an improvement on other "hand-winding"
methods. It helps locate the loop: the second crossing of your hand is
near your fingertips and away from the other two turns. This helps you
to locate it, pick it up, and wrap it around the other two strands.
Setting the knot usually requires holding the loop in your teeth and
pulling both ends with your hands.
If you need tension then you could also try:
Form a bight in the standing end and use it to tie a Directional
Figure 8 Knot. Pass the tail round the hook below and through the
Directional Figure 8 Loop, and pull tight. Complete the knot with two
Half Hitches below the loop.