A 35-foot vessel caught fire and sank this morning in the Hawaii Kai Marina.  Firefighters were called at 9:13 a.m. and had the flames under control just after 9:30 a.m.  Fire Captain Terry Seelig says the boat was undergoing maintenance work and gasoline vapors and a spark are believed to be the cause of the fire. It's owned by Sea Breeze Parasailing. Workmen set the boat free so it wouldn't endanger the dock at the marina. Damage to the boat was estimated at $60,000.