So I was reading wikipedia about paradoxes and eventually got to the part about time travelling. Among the list were various examples of paradoxes involving time travelling, and a movie I saw came to mind. I can remember most of the movie, but I can't remember a single name of any character.
It starts out with a woman walking on a dock towards a ship looking very tired. A friend of hers asks her what's wrong, and she responds that she didn't get much sleep. So she boards the boat with about four other people, and their ship is destroyed by a rogue wave or something. They find a ship that looks kind of like the titanic (it isn't) ad decide to explore. Not a soul is found on board, but some strange things start happening.
The main character finds various articles of hers that she didn't bring with her on the ship. Throughout the movie, there are scenes where, for example, she drops a locket. She looks down through the grates and finds a huge pile of those lockets at the bottom.
There also appears to be a murderer onboard, because everyone dies except the main character. About halfway through the movie, the original group reappears on board the ship, totally unharmed and with another version of herself. We find out that she is actually the murderer, who is hellbent on killing the other version of herself.
I also remember a scene involving a woman with short red hair and she's crawling away from the main character into a huge pile of her own bodies.
Somewhere near the end, the main character gets off the boat and back to civilisation. She finds her son in her house with herself, who hits her son. She then kills the other self inside the house and takes her son, but ends up killing him. Apparently the whole event erases her memory, because she stumbles to the dock from the beginning of the movie where her friend asks her what's wrong, and the whole event begins anew.
Sorry for the vague description, but this is bugging the hell out of me. Any suggestions on what this movie might be are greatly welcomed.