Gian Carlo Coppola and his friend Griffin Patrick O'Neal, in Washington to work on a movie, took a break from the shooting last weekend and rented a small motorboat so they could spend the Memorial Day holiday enjoying the sunshine on the South River near Annapolis.

Three hours after they rented a 14-foot craft, Coppola, the son of movie director Francis Ford Coppola, was killed in a freak accident on a popular stretch of the river. O'Neal, the son of actor Ryan O'Neal, received a minor shoulder injury.

Coppola, 23, suffered massive head injuries after he was struck by a towline connecting two larger boats, according to Ernie Mosby, a spokesman for the Maryland Natural Resources Police.

One of the larger vessels was towing the other to a marina when Coppola's 14-foot rented boat ran into the towline. Coppola, at the helm of the smaller boat, was pitched backward by the force of the blow and struck his head on the deck.

The accident occurred at 5:15 p.m. about three miles south of the popular Pier 7 marina on the South River in Edgewater, according to Mosby.

Emergency medical teams took Coppola ashore and tried to revive him. He was taken to Anne Arundel General Hospital where he was pronounced dead about 6:20 p.m., Mosby said.

O'Neal, 21, a passenger in the boat, suffered a shoulder injury in the accident but refused treatment, Mosby said.

Mosby said that the boat was traveling about 15 to 20 knots when the accident occurred and that alcohol was not a factor. The names of those aboard the other boats have not been released, and an investigation is continuing, Mosby said.

Coppola and O'Neal were working on a film, "Gardens of Stone," that is being directed by Coppola's father and is being shot at Arlington National Cemetery.

Lynn Hale, a publicist for Tri-Star Pictures, which is producing the movie, said Coppola's son was a videotape camera operator and O'Neal, the brother of actress Tatum O'Neal, has a small acting role.

In an earlier, unrelated development, Arlington County police said O'Neal had been arrested Friday and charged with carrying a concealed weapon -- a knife -- and with traffic violations after a sports car he was driving was stopped in Rosslyn.

O'Neal's agent, Barbara Lawrence, said she did not know why O'Neal was carrying a weapon.

Lawrence said O'Neal and Coppola met while working on the movie and had decided to spend the day boating because of a break in the shooting for the holiday.

Hale said the Coppolas had worked on several movies together, including "Cotton Club," "Rumble Fish" and "The Outsiders."

The older Coppola is best known for his work on the Academy Award-winning movie, "The Godfather," and the Vietnam War epic, "Apocalypse Now."

Hale said Coppola was "devastated" by the news of his son's death and described their relationship as "very, very close."

Lawrence said she had spoken with the younger O'Neal since the accident and that he was was "very shaken," but was expected to resume his work in the film.