It was traditionally used by sailors to tie a line to the bottom of a square sail.

The square sail was efficient in a following wind.

It had a single tall mast and a flat, square sail.

Even the addition of square sails and oars was found to be too slow.

The ships have a single mast with a square sail.

Then the square sail dropped, and the oars fell deep into the water.

On a square sail, however, this part is an edge rather than a corner.

You can't beat the square sail for an ocean passage.

The yard exists to allow square sails to be set to drive the ship.

The big square sail bellied out, full of a following wind.