A duck boat suffered a fire in its engine room at McCovey Cove, California.  The vessel sent out a distress call and the Coast Guard dispatched a rescue boat and the San Francisco Fire Department dispatched a fire boat to the scene.   The Coast Guard rescued the 28 people on board and tranported them to shore.   The Fire Boat extinguished the fire.    No reports of injuries.   The cause of the fire is under investigation.  A report states the fire started after the engine overheated.