Probably the single most common ballad is the sailor-returning type. Sweet Young Woman is moping around town, and is approached by Strange Man. Were this a Nick Cave ballad, it'd all start to go to hell at this point, and we'd be treated to a lyrical description of Strange Man bashing her head in with a rock, but fortunately for Sweet Young Woman, traditionally Strange Man just asks her about her sweetheart. (I quite like Nick Cave, but then, I'm a weirdo.) Since everyone loves to tell their tale of woe, Sweet Young Woman recounts how her one true love went to sea seven years ago (it's always seven years--this appears to be set in stone.) and has been lost at sea. Being a soppy romantic of the sort beloved by ballads, (and apparently independantly wealthy) Sweet Young Woman will never take another sweetheart in honor of his memory. Convinced of her faithfulness, Strange Man brings out the ring that was the token of their love, and lo and behold, it's the Sweetheart, come home at last, and it's been so long that she didn't recognize him. She swoons, they get married, and the last verse is spent moralizing about how young women should stay faithful to their sweethearts when they're at sea.
This is so formulaic and reoccurs so often that one gets the impression a matrimony-minded sailor in days of yore could just pick up any old gold ring and stroll inland until he finds a particularly nearsighted Sweet Young Woman moping about.
My personal favorite is a variant on this called "Willie Taylor" wherein the Sweetheart is impressed as a sailor against his will just as he and Sweet Young Thing are about to be married. Sweet Young Thing, being a bit more bloody-minded, pulls in that other archetype beloved of Shakespeare and folksongs alike, dresses up as a boy and goes to sea in pursuit of him. Eventually the improbably noble captain of her ship realizes that his cabin boy's got cleavage and rather than avail himself of this fact, helps Sweet Young Thing find her Sweetheart. But wait! That rat bastard's gone and gotten married someone else! Jerk. So, having learned a trick or two as a cabin boy, our nameless Sweet Young Thing shoots him in front of his bride and storms off into the sunset. There may be a moral to this story, other than "Don't mess with chicks who learned to fire a cannon in the Navy," but I choose to ignore it, probably because the version I've got has a very entertaining "Uuuuugughh...thump!" sound at the shooting bit that cracks me up. Yes, I'm easily amused.