The fire was reported about 1pm, said Pol Lt Col Sornthip Chukaew, an investigating officer at the Tha Chatchai Police Station, reports the Bangkok Post.
Firefighters and civilians helped put out the flames, which spread from the stern to the bow of the 12-metre craft named Jimmy Blue. Only the prow of the vessel remained above water.
There were no people on board when the fire started, and no casualties were reported.
Oil boom barriers had been placed in the water to prevent potential oil spills.
The catamaran can carry up to 17 people ‒ 14 passengers and three crew members. It was permitted to sail in local waters between Ranong and Satun provinces after receiving a licence in 2014.
Following an inspection, officials said the blaze might have originated from an electrical short-circuit.
Further investigation was underway to determine the cause of the fire.