You can just hear the pitch for the thriller Deep Rising: ”It’s Alien meets Titanic!” Yes and no. The plot does pit Treat Williams’ renegade against a voracious sea monster lurking in a foundering cruise ship. But its execution by writer-director Stephen Sommers is strictly second-rate. The talented Williams seems a poor man’s Harrison Ford, gamely wisecracking in the face of death, while Famke Janssen’s jewel-thief love interest and Anthony Heald’s double-crossing ship owner are as two-dimensional as paper dolls. Before long you’ll be rooting for the film’s one charismatic presence: the impressively slimy computer-generated serpent. For the actors, have a batch of popcorn ready to throw at the screen. C-