Nautical Folklore

Sailors from time immemorial have had their own brand of folklore. Much of it is borrowed from that of landlubbers, Norse Mythology and Greek Mythology, for instance, but sailors have had their own unique twists. These types of tales are what they sang to each other during long, boring voyages. They included tales of great deeds, quirky superstitions, fantastic creatures and day-to-day life on the sea. Sailor lore also has such things as haunted islands and accursed ships. Sometimes sailor tales were sung rather than told, especially as sea chanties provided rhythm to help with their work.

There are a few fairly good compendiums of nautical folklore. Two of them include Folklore and the Sea by Horace Beck and Seafaring Lore and Legend by Peter Jeans. By fortunate coincidence the photo of Horace Beck looks exactly like the sort of Father Neptune that would be telling these stories.

Tropes from nautical folklore include

 * Blood Magic: In some parts of the West Indies, at least until recently, it was common to use animal blood to christen a fishing boat. Most of the Western World however is satisfied with Champagne.
 * Born Unlucky: If the bottle fails to break during the christening of a ship.
 * Case in point—the Costa Concordia which struck a reef and capsized in shallow water on 13 January 2012. Allegedly, the Champagne bottle didn't break at its christening in 2006.
 * Cats Are Magic: Having a cat aboard was thought of as bad luck, or good luck, depending on whom you ask. Also, in some Caribbean myths, mer-people can transform into cats.
 * Do Not Taunt Cthulhu: Numerous variations. Don't set out on Friday. Frey is in charge of the Valkeries and you naturally do not want her to arrive early. Don't set out on Thursday, either: That is Thor's day and you don't want to offend the guy in charge of storms. Oddly enough though, Odin is apparently in a good mood in this instance for if you set out on Wednesday(Wodensday) you get good luck.
 * Do not take a murderer, a debtor or a woman aboard: It's bad luck. Don't build a ship out of black walnut, either. No one is sure why not. Just don't.
 * Also don't rename a ship. And never name a ship after a vessel that had bad luck(which is why nobody names their ship Titanic).
 * Heck, just stay on shore.
 * Due to the Dead: US Midshipmen place coins in the grave of John Paul Jones. Presumably he will reward them with a due share of Badassery.
 * The Drunken Sailor: Generally the cause of the folklore to start with. A Tall Tale of tall ships over a tall draught of rum.
 * Eldritch Abomination: The whole ocean, just to start with.
 * Ethnic Magician: supposedly all Finns are Wizards.
 * Hubris: Do not give a merchantman a grandiose name. That is Tempting Fate. Passenger liners and clipper ships were often an exception to this, having names like Lightning, or even Sovereign of the Seas. Though the clipper that lasted longest was just named Cutty Sark(Which means short skirt because of a Scottish legend that one man who was being chased by witches noticed one of them wearing a "cutty sark" and...) rather then something grandiose.
 * Executives for the White Star Line said of the Titanic that God Himself could not sink the ship. In Titanic, Cal Hockley (Billy Zane) parrots the company line before boarding.
 * The executives of the White Star Line seemed to learn their lesson after the Titanic sank. The Titanic was the second ship of four planned ships in the Olympic-class. The third ship was scheduled to be christened the Gigantic, but was renamed the Britannic. (The Olympic had collided with a Royal Navy cruiser in 1911.) The renaming was for naught—during World War I, the Britanic (which was in service as a Royal Navy hospital ship) struck a mine off the coast of Greece and sank. The fourth Olympic-class was cancelled.
 * Warship names, on the other hand, invoke this; many were (and still are) given grandiose and ferocious-sounding names like Victory, Warrior, or even truly fate-tempting ones like Invincible and Indefatigable.
 * I Owe You My Life: According to one story a Mermaid was stranded on a beach and found by a kindly Scottish boatbuilder. She offered him a wish and his wish was that no boat he ever built would ever sink. According to the story, his descendants are still building boats and are still famed for their craftsmanship.
 * Kraken and Leviathan
 * Father Neptune: Who else is fit to be The Storyteller?
 * Flying Dutchman: And several other ghost ships.
 * MacGuffin: Amongst seafaring cultures, it was common belief that a child born "in the caul" (that is, with the amniotic sac still attached and covering his/her head), is lucky and cannot drown. In fact, these membranes were sometimes preserved and sold to sailors for a small fortune, because the sailors would carry them for luck and protection at sea. Now a Forgotten Trope in much of the world, as many times the amniotic sac is ruptured artificially by the doctor or midwife.
 * Not quite forgotten- still a popular folklore in the South and among the homebirth crowd. Also has some justification in that a labor and birth with a nice squishy layer of water cushioning the contractions is usually MUCH easier than one without, especially in the case of artificially rupturing the membranes.
 * The expression "born in the shirt" (about the same situation) is a general characteristic of a lucky person in Russia.
 * Mer Tropes
 * Names to Run Away From Really Fast: An Accursed Person is a "Jonah". You don't want him aboard.
 * Our Ghosts Are Different: Dolphins and albatrosses are the reincarnated souls of dead sailors. Do not kill either of them.
 * Pirate Booty: Often with a curse on it, naturally enough.
 * Red Sky, Take Warning
 * Sea Monster
 * Selkies and Wereseals
 * Shapeshifting Lover: Mermaids and Selkies (seal people) often do this.
 * Tropes At Sea
 * Turtle Island
 * Wooden Ships and Iron Men
 * ~You Can't Fight Fate~: If a sailor is pulled overboard by a wave, that's a sign that "the sea will have its own".
 * In fact, learning to swim was considered Tempting Fate.
 * The superstition still lives and even branched into a different medium: many flyboys absolutely hate skydiving, as it's believed that learning the skill means that you'd need it later.