If you want true, active
superstition, look no further than
Britain's
Royal Navy (the "Britain" is a sop to all other
monarchies).
In the RN, the form you have to fill in for any collision or grounding of your ship is Form 232. No-one mentions the number 232, if they have to it is always "231 and a bit". It gets to the point where HMS Lancaster, in sequence of pennant numbers, should have been F232, but on protest it was changed to 229 to avoid making the ship unlucky from birth.
Another example, a friend of mine who does not want to be "tapped" or conscripted as a submariner, touches wood every single time he hears the word submarine or submariner.
Another one heard is a Captain who banned Earl Grey tea from his ship since it caused accidents - apparently the last time the ship had Earl Grey on board, one of the lifebuoys came loose, set off a massive smoke float in the middle of Portsmouth harbour, they had to call up on the Radio to tell the Harbourmaster it wasn't real distress, then try to pick it up, they subsequently lost it after the smoke burned out, and spent several hours hunting. When they finally found it, they had to return to port as a missing lifebuoy is an A1 OPDEF (not allowed to go to sea).
Other things not to mention/have aboard are:
-Finns: Jack perceives Finns to be the root of all storms and evil, and will go out of his way to avoid them
-Eating Fish at sea: for some reason a lot of sailors object to this - they see it as eating their brothers and bad luck to eat them