Sailors were particularly superstitious in this regard, often refusing to ship out on a Friday. According to unverified legend (very likely untrue), the British Navy commissioned a ship in the 1800s called H.M.S. Friday, in order to quell the superstition. The navy selected the crew on a Friday, launched the ship on a Friday and even selected a man named James Friday as the ship's captain. Then, one Friday morning, the ship set off on its maiden voyage... and disappeared forever:
http://people.howstuffworks.com/friday-thirteenth1.htm