His public defenders declined to comment as they left the courthouse.
The verdict comes more than four years after the September 2019 tragedy, which prompted changes to maritime regulations, congressional reform and several ongoing civil lawsuits.
Relatives of those killed hugged one another and wept outside the courtroom Monday after the verdict was read.
Clark and Kathleen McIlvain, whose son Charles died aged 44, said they were relieved that there is finally some accountability for their loss.
“We are very happy that the world knows that Jerry Boylan was responsible for this and has been found guilty,” Clark McIlvain said.
The families also applauded and cheered outside the courthouse when the federal prosecutors arrived for a news conference to discuss the case.
“The captain is responsible for everything that happens on the ship, including, most importantly, the safety of everyone on board that ship,” US Attorney Martin Estrada told reporters.
While Estrada said Boylan “failed, utterly failed” in those duties, he declined to comment when asked if the boat’s owners would be charged now that prosecutors have secured a guilty verdict against the captain.
The Conception was anchored off Santa Cruz Island, south of Santa Barbara, when it caught fire before dawn on the final day of a three-day excursion and sank.
Thirty-three passengers and a crew member perished, trapped in a bunkroom below deck. Among the dead were the deckhand, who had landed her dream job; an environmental scientist who did research in Antarctica; a globe-trotting couple; a Singaporean data scientist; and a family of three sisters, their father and his wife.
Boylan was the first to abandon ship and jump overboard. Four crew members who joined him also survived.
Although the exact cause of the blaze remains undetermined, the prosecutors and defence sought to assign blame throughout the trial.
The US Attorney’s Office said Boylan failed to post the required roving night watch and never properly trained his crew in firefighting. The lack of the roving watch meant the fire was able to spread undetected across the 75-foot (23-metre) boat.
Boylan’s lawyers sought to pin blame on boat owner Glen Fritzler, who with his wife owns Truth Aquatics, which operated the Conception and two other scuba dive boats, often around the Channel Islands.
They argued that Fritzler was responsible for failing to train the crew in firefighting and other safety measures, as well as creating a lax seafaring culture they called “the Fritzler way,” in which no captain who worked for him posted a roving watch.
The Fritzlers have not spoken publicly about the tragedy since an interview with a local TV station a few days after the fire. Their lawyers have never responded to requests for comment from Associated Press, including on Monday.
Kendra Chan, 26, was killed on the Conception, along with her father, Raymond “Scott” Chan, 59. Vicki Moore, who was Raymond’s wife and Kendra’s mother, said Monday that justice was served.
“A strong message came through that if you are captain of a boat, you are truly responsible and there are consequences if you don’t follow the law,” Moore said after the verdict.
While the criminal trial is over, several civil lawsuits remain ongoing.
Three days after the blaze, Truth Aquatics filed suit under a pre-Civil War provision of maritime law that allows it to limit its liability to the value of the remains of the boat, which was a total loss.
The time-tested legal manoeuvre has been successfully employed by the owners of the Titanic and other vessels, and requires the Fritzlers to show they were not at fault.
That case is pending, as well as others filed by victims’ families against the coastguard for alleged lax enforcement of the roving watch requirement.
The Channel Islands draw boaters, scuba divers and hikers. Five of the eight Channel Islands comprise the national park and Santa Cruz is the largest within the park at about 249 square kilometres (96 square miles).