Four hundred convicts and mental patients -- "the worst element" in Cuba, according to authorities who threatened the captain with a firing squad if he refused to take them -- arrived today in Key West aboard a single boat, the America.

Not a single relative of the Cuban-Americans who chartered the America was on board the 100-foot-long catamaran, which carried 700 refugees, the largest group to arrive on the biggest day of the exodus.

"They told us we are in Cuba now, under Cuba regulation. And that we'd take what they gave us or they'd take the boat," said Tom O'Toole, captain of the America.

And that may be only the beginning. The same authorities threatened to send "8,000 scum" to the United States.

Two who came on the America went berserk during the trip and had to be lashed to the boat's railings, according to a beleaguered Carey Cole, who served as skipper for this trip.

"One of the men they tied up tried to kill people. He tried to strangle them," said Rick Mena, a Miamian who accompanied the America to Mariel, near Havana.

Michael Cabreja, a Behamian crewman aboard the America, said the other man "was just a little crazy. He wanted to jump overboard. He kept screaming."

The America was so overloaded that the U.S. Coast Guard had to take 200 of the refugees off the boat in the middle of the Florida Straits and bring them to shore aboard the cutter Dauntless. The America came in at 4:30 a.m. t

Cole, who waited 16 days in Mariel harbor, was furious over the passengers he'd been forced to bring to Key West. He told Cuban authorities his boat could safely hold only 350 people. "I protested them coming aboard," Cole said.

"I said I didn't come down here to pick up these people. They said if I didn't take them, they would seize my boat, name it the Fidel and put me before a firing squad.

"One of the Cubans said the America was going to lead a present to the U.S. of 8,000 scum. They wanted to put 8,000 people into Key West in one day to inundate Customs."