Chao Chen, 73, and his son, Jun Chen, 48, of San Diego died after the 26-foot sailboat flipped over in the San Diego Bay. They were declared dead at the scene.
A woman remains in intensive care for hypothermia, and seven others were also injured, including several children.
Of those injured, no one suffered life-threatening injuries.
Among them were two young adults with undisclosed special needs, and a 10-year-old girl and an 11-year-old boy who were wearing life jackets, authorities said.
Most of those on board were members of an Asian family, and investigators had to bring in interpreters to speak to them, San Diego Fire-Rescue spokesman Maurice Luque said. He did not know what language they spoke. No victims' names were immediately released.
Investigators were trying to determine why the boat flipped over then sank near Shelter Island.
There was speculation that the boat's keel was not deployed, allowing for winds to push the vessel over, according to Luque.
The Associated Press and City News Service contributed to this report.