+1 sight range.
Before the advent of detailed nautical charts (but after sailors trusted only luck to reach shore safely) a rutter was a mariner's handbook of sailing directions for navigation – termed a periplus ("sailing around" book) by ancient Mediterranean sailors. These were jealously guarded by navigators and pilots throughout the Middle Ages, for they were the personal record of all one knew about the trade routes they had explored or sailed. During the Renaissance, rutters shared among city merchant-traders made the likes of Pisa, Genoa, and Venice incredibly wealthy. The Age of Discovery brought rutters to even more prominence, as they were the nautical record of how to reach those distant places again. Eventually, all this private knowledge got replaced by nautical charts, and sailing became far less adventurous.