A tugboat captain's error caused an articulated tug and barge (ATB) to strike and damage the fending system protecting the Hylebos Bridge in Tacoma, Wash., last October, the National Transportation Safety Board (NTSB) said Tuesday.The tugboat Olympic Scout, operated by Olympic Tug & Barge, was assisting the ATB Montlake/Sodo, also operated by Olympic Tug & Barge