Police inspected the 10-tonne trawler that was towed to the Wat Sang Sonk pier on Friday morning.
The body of trawler captain Uthen Saetan, 39, was found in the boat cabin.
His older sister, Wanthana Saetan, told police that Uthen left for the fishing trip at 4pm on Thursday and never returned. The family heard about the trawler sinking the following morning.
Police suspect that Uthen was in the cabin whose door and windows were closed during the rainstorm and hence couldn’t get away in time when the boat sank. The crew members, who were outside, managed to swim to safety. Uthen’s body was sent for autopsy to the Police General Hospital in Bangkok.