The U.S. Coast Guard says the sinking of a tugboat working on a new bridge between Portsmouth, N.H., and Kittery, Maine, was due to human error. And the Coast Guard is considering an enforcement action against the operator of the tugboat Benjamin Bailey that sank on Oct. 24, while moored to a barge at the construction site of the Memorial Bridge. No one was injured, but the tug spilled an estimated 225 gallons of diesel fuel into the Piscataqua River. The Coast Guard’s report on the sinking was obtained by Foster’s Daily Democrat. The report says a lack of attention to the mooring position of the boat as the tide dropped was a factor in the sinking. The tug was later raised and taken to shipyard for salvage.