Gian Carlo Coppola, 23, of Apple Valley, Calif., suffered massive head injuries and was pronounced dead on arrival at Anne Arundel County General Hospital at 6:20 p.m. Monday, a hospital spokeswoman said.
The Memorial Day accident occurred on the South River, off the shores of Edgewater, a tourist town with numerous marinas.
Police said the only other person aboard the boat was Griffin Patrick O'Neal, 23, son of Ryan O'Neal. Griffin O'Neal suffered a minor shoulder injury but refused treatment, police said.
The two young men were visiting the area because Coppola's father has been shooting a movie, "Gardens of Stone," at Arlington National Cemetery outside Washington.
O'Neal had been arrested in nearby Rosslyn, Va., a Washington suburb, early Friday and charged with reckless driving, driving without a license and carrying a concealed weapon--a 6- to 8-inch ballistic knife, police spokesman Ken Rosenberg said.
O'Neal's relationship with his father made the news in May, 1983, when they got into a fight and Ryan knocked out two of Griffin's teeth. The younger O'Neal called police to their Bel-Air, Calif., home but he later refused to press charges.
Griffin O'Neal also spent a year in a drug-and-delinquency rehabilitation center in Hawaii.