The clove hitch. One line, one rail, four steps.

1. Take the line over the rail and bring it around, crossing over the standing part.
2. Take the working end around the rail again to make a second turn.
3. Pass the working end underneath the crossing you just made.
4. Pull both ends to tighten.

It is a simple, versatile knot for tying a line to a rail or post. It is quick to tie and easy to adjust. It can slip if the load is not steady, so use it for light jobs like fenders, or add a second knot.