There are many stories why bananas have been thought of as bad luck on boats.  This is only one of the nautical superstitions that I know of and is particularly prevalent amongst watermen.  Many stories have banana oil rubbing off on ones hands and “spooking" the fish; therefore the fish don't bite.  There is always the story of a crew member slipping on the banana peel left on the deck.  Some say that bananas give you the runs so you are always in the marine head and can't catch fish because you are busy "draining the pipes".  Many other stories are told about bad luck and bananas, however the one that I find most plausible is a historical one.

Back in the days of the transatlantic crossings by wooden sailing ships many hazards would befall the captains, crew and passengers. Disease, pirates, shipwrecks, storms, etc., claimed the lives of a good percentage of the captains, crew and passengers attempting the dangerous voyage.  Needless to say, a transatlantic crossing in the 17th and 18th centuries was a very risky endeavor.  Often the vessels would stop along the way in tropical islands to gather provisions such as food and water.  There the passengers and crew would often purchase wooden crates of bananas from the locals and bring them aboard the ship.  These crates would have all manner of critters in them such as bugs, spiders, vermin and snakes.

Watermen are a mysterious lot.  While we are known for our simple pragmatism, we also have many odd quirks.  Superstitions have been prevalent on almost every vessel I have worked on.  I feel that this is due to the nature of a waterman in that he sees the randomness of the world around him juxtaposed with the rhythmic, seasonal flows of nature and then tries to reconcile these observations into some sort of personal and/or environmental order.  As Stevie Wonder (a blind man) pointed out so eloquently: "When you believe in things you can't understand, that's superstition".