SCUBA divers have launched an appeal to find relatives of a Cardiff crew member who was killed when their ship was torpedoed by a U-boat in the First World War.   Members of the Severnside branch of the British Sub-Aqua Club (BSAC) have been exploring and investigating the remains of the SS Baygitano for the last three years and recently won an award for their archaeological efforts.   The huge vessel was sunk by U-boat UC-77 during the First…