Mariners do best when they avoid the edges of the sea – the shoals, rocks, and other hard spots. Coming into contact with the edges of the sea at other than a slow walking speed can ruin an otherwise pleasant voyage. Unfortunately, though, vessels have been making hard contact with the edges since Noah’s Ark grounded on Mount Ararat, rendering the Ark unseaworthy. For a while, it was thought that the leadline would reduce groundings, but one can’t be swinging the leadline constantly. Lighthouses were another early means of identifying hard spots by means other than direct contact.