The Petchthara 7 was on its way back from the popular Koh Larn - also known as Koh Lan - where the tourists from Buriram province had spent the day on Tawaen beach.
Ferry captain Kamtan Tungtaisong, 47, noticed his vessel was going under around 3pm and managed to call other boats to assist in getting the passengers off safely, said Colonel Sakatat Pumpanmuang, of Pattaya Police Station.
Officers will investigate the cause of the sinking, the colonel said.
A severely overloaded vessel sank between Koh Larn and the mainland Pattaya Pier on November 3, 2013, with the loss of seven tourists.
The victims were a Russian boy, a Polish couple, a man from Hong Kong and three Thai passengers.
A ferry, the Ao Nang Princess 5, caught fire and sank on April 8 this year travelling between Krabi and Phuket with passengers and crew forced to jump into the sea to escape the flames.
Israeli Shani Maril, 12, was killed. Most passengers lost all their possessions and have not been compensated.