Unit 1 was traveling south on the ICW. Operator noticed the fire alarm going off. He turned over control to subject. Operator went to the engine room to investigate the smoke was overwhelming at that time the vessel was shut off and both men got in the life raft and contacted the Coast Guard. After the office spoke we the fire investigator from Traveler's Insurance the cause of the fire on the "True Lady" seems to have come from the exhaust. The Fire investigator's opinion was that the raw water intake hose failed on the port engine which caused the exhaust to over heat because it was not getting cool water to it. That in turn started the fire which spread throughout the vessel.