As the Sea Venture approaches the shore of the Devil’s Isles, the boatswain takes soundings, measurements of the depth of the sea by dropping a weighted rope over the side that is knotted every six feet. Each knot is a fathom, and the boatswain counts the knots as he lets out the line. First it is thirteen fathoms, then seven fathoms, then four fathoms. Finally everyone knows why the islands are uninhabited and feared, as no ship has ever landed or anchored safely in these waters because of a massive reef encircling the islands. There are the remains of many ships wrecked on the reef.