Witnesses said the 90-foot yacht flipped as it was being launched at about 9 p.m. Sunday.
It was a chaotic scene as rescuers rushed in to pull the six people aboard out of the water. There were eyewitness reports that crews had to use axes to reach people near the engine compartment.
Two of the rescued people were taken to the hospital to be checked out, said Petty Officer Jordan Akiyama of the U.S. Coast Guard.
One of the crew members, Wade Benda, said he still doesn't know what went wrong, but he's glad he got out alive.
"To see it all in the water like that it's kind of tough," he said.
Benda, the yacht's mechanic, is part of the team that spent two and a half years building the multi-million dollar vessel.
The yacht rolled without warning, leaving Benda and four other crew members trapped inside.
"I'm relieved that I'm here on the ground and I just want to thank the good Lord above that, I'm here it was just a scary moment," Benda said.
Benda said he thinks the boat's starboard stabilizer hit some rocks when it initially rolled near the boat ramp. He said they tried to "thrust" the boat back into deeper water. Shortly after that they got into deeper trouble
"We just braced ourselves," Benda said. "I have no idea what went wrong."
A team has been sent in to assess pollution from fuel aboard the vessel. So far, no sheen has been observed, but the yacht has been boomed off as a precaution.
An investigation is pending as to why the yacht sank, Akiyama said.