A clove hitch is frequently used on boats for securing a line around a rail, post, or other cylindrical structure. It is a secure temporary knot used, for example, to hang fenders to the boat’s rails or lifelines, as shown in this series of photos. Advantages of the clove hitch include that it can easily be adjusted or undone.
Begin tying the clove hitch by bringing the line over the rail as shown here, or around a vertical post. Maintaining some tension in the line helps while you make the knot.