A recreational boat that sank in the San Francisco Bay on Tuesday, killing at least one person, was slammed by a wave before it rolled on its side and began to sink, officials said on Wednesday.
Of the 20 people onboard, 16 were rescued on Tuesday, and another three remain unaccounted for. One person, Clifford Joseph Boisa, 79, of Sutter County, Calif., outside Sacramento, was brought to shore in distress and died of his injuries.
Captain Jarod Toczko of the U.S. Coast Guard said at a news conference on Wednesday that the people on the boat “were all close friends and family.” According to the San Francisco Fire Department, the passengers, who were not from the Bay Area, had been spreading the ashes of a loved one in the bay’s waters.
Investigators said they don’t yet know exactly why the three-deck, 49-foot cabin cruiser had sunk to the bottom of the bay. Captain Toczko said the boat, called the Volare, lost stability after being hit by a wave, and several people tumbled overboard as it rolled onto its right side.
The boat then began to take on water, he said. By the time rescue workers arrived, around 3:30 p.m., the two lower levels of the boat were already submerged.
“All indications are that things happened very quickly when the vessel took on a wave over the side,” Captain Toczko said.
He said that the search for the three people still missing would be suspended on Wednesday evening.
Captain Toczko said that rescue crews had not yet been able to find the sunken boat, which went under near Alcatraz Island in a part of the bay that is 130 feet deep with strong currents. He said that the missing passengers could have been inside the boat’s two lower, enclosed compartments when it rolled.
“There is a high possibility that individuals could have been trapped inside the vessel,” he said.
The winds were light across San Francisco and the bay on Tuesday morning and picked up in the afternoon, as they often do in the summer, causing choppy waters. At the time the boat capsized, “it was definitely a little breezier than what it normally would be, but not by a ton,” said Brian Garcia, a meteorologist with the National Weather Service. While there is no instrumentation on the bay that measures wave height, Mr. Garcia said that waves may have reached about four feet high.
At the Wednesday news conference, Captain Toczko noted that rescue crews had searched for nearly 24 hours and covered 950 square nautical miles. When asked if the three missing passengers could still be alive, he said, “We always hold out hope, right? That’s why we’re still searching.”
The authorities did not identify the boat captain, but said he had been brought to a hospital and has since been released.
John Edward Boisa of Stockton, Calif., owns the Volare with his wife, according to registration documents.
Mr. Boisa, a younger brother of Clifford Boisa, has posted on social media about earlier trips on the boat. He did not respond to voice mail messages left on his phone on Wednesday.
The group on the boat had left from San Francisco and visited Angel Island, a scenic state park, before the accident. The boat sank in the narrow passage between Alcatraz and the northern shore of San Francisco, which acts as a bottleneck that quickens the current and generates big waves, said Steve Jones, a local marine surveyor with decades of boating experience.
The area can be “very treacherous for any kind of boat,” he said, particularly now since the Bay Area is experiencing king tides.
Christine Kaplan, who runs a boating fuel center that hosted rescue workers’ emergency operations on Tuesday, said the entire group of survivors was drenched when they were brought ashore. Some had bruises and scrapes on their heads. Others were missing their shoes.
“It was very scary,” said Ms. Kaplan, 72. “Everyone was cold and wet, didn’t look like anybody didn’t get into the water.”
Amy Graff contributed reporting and Kirsten Noyes contributed research.