The single bowline on a bight comes in handy whenever you need an eye in the center of a line. It can be tied quickly, doesn't jam tight, and you don't need an end of the line to tie it. To get your securing lines taut, a single bowline on a bight is a good knot to use for securing equipment or cargo.
Tie the knot well up on the standing part, run the bitter end around a stanchion or through I pad eye and back through the eye of the knot. Heave back on the bitter end in a line between the knot and stanchion or padeye. This gives the same effect as having a block on the line at the knot and, discounting friction, doubles your pull. Heave it taut and secure the end.
