Moviegoers are likely to be at sea over what to take in at the multiplex this weekend as Ocean's 13 opens against Pirates Of The Caribbean: At World's End. Although Pirates had been expected to dominate the box office during its first weeks in release, it had already been overtaken by the R-rated comedy Knocked Up by its eleventh day. And while Ocean's has a huge all-star cast and brand recognition, it, too, may not be able to overcome the enthusiastic word-of-mouth that Knocked Up has generated. (It was the top film at the box office from Monday through Thursday.) There'll also be counter-programming competition from the horror film Hostel Part II and from the family animated movie Surf's Up, about a surfing penguin.