When Erik Anfinson set sail Thursday on San Francisco Bay in his 130-foot Alcatraz Clipper with more than 400 passengers aboard, he didn’t expect to end the night a hero.

As the 45-year-old Novato resident departed Alcatraz Island about 8:45 p.m., he heard an alarming broadcast over the marine information system from the Coast Guard. A 31-foot recreational vessel had hit a rock in the water and was about to sink with ten people on board, said Lt. Nicole Emmons with the Coast Guard.

Anfinson, also known as Capt. Tubby, immediately diverted his ship toward the sinking vessel.

“I noticed it was taking on a lot of water very quick,” he said. “I’ve done (rescues) with smaller boats, fewer people, but this was the largest rescue for me.”

Anfinson sidled up to the sinking ship, but he said neither one had a rope long enough to attach the two boats together.

“I maneuvered the boat right up alongside of it,” Anfinson said. “We had the two boats rafted up basically side by side, not tied together.”

With his crew of five, Afinson helped the ten adults that were standing at the bow of the submerging boat with life jackets jump over into the his vessel.

“A decision that I made was to pull them off the boat before they made it into the water,” Anfinson said, adding that the water temperature was about 54 degrees.

As the last person jumped aboard to safety, the 438 other passengers on-board erupted in cheers.

“We had beautiful weather. The conditions were perfect and everything was as smooth as can be. I’m glad it wasn’t eventful,” Anfinson said. “We do drills so we are ready for this kind of stuff. And the crew is always prepared.”

The damaged boat ended up sinking in the bay, Emmons said.

There were no injuries reported as Anfinson brought those rescued back to San Francisco’s Pier 33 safely.

“It was a good thing, (Anfinson) heard our broadcast and went over there and helped them out,” Emmons said.

But for Capt. Tubby, who earned his sailing license at age 19, he was just doing his job.

“People were calling me a hero,” he said, “I just do my job, this is what I get paid for.”

Sarah Ravani is a San Francisco Chronicle staff writer. Email: sravani@sfchronicle.com Twitter: @SarRavani