The Coast Guard says the incident happened around 2 p.m. between Richmond and San Rafael.
Steve Fenton, the good Samaritan tells ABC7, the conditions on the water were rough at the time, when he noticed the sinking sailboat and went to help.
MORE: Crews rescue 9 people from sinking sailboat in SF bay
No one was hurt.
It's unknown if the boat is fully submerged.
Nine people were rescued from a sinking sailboat in the San Francisco Bay back on May 24.
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