Taut-line hitch

The taut-line hitch is an adjustable loop — slide it up the line to tighten, and it holds. It's the knot that keeps a tarp drum-tight all night.

When to use it

tarps      hold tension as the fabric stretches
clotheslines  tighten without retying
guy lines   adjust for wind or sag

The trick

Two wraps inside the loop, one outside. Load it, and it locks; slide it, and it moves.