As part of a project to extend the Massachusetts Turnpike, respondent Dutra Construction Company dug a trench beneath Boston Harbor using its dredge, the Super Scoop, a floating platform with a bucket that removes silt from the ocean floor and dumps it onto adjacent scows. The Super Scoop has limited means of self-propulsion, but can navigate short distances by manipulating its anchors and cables. When dredging the trench here, it typically moved once every couple of hours. Petitioner, a marine engineer hired by Dutra to maintain the Super Scoop's mechanical systems, was seriously injured while repairing a scow's engine when the Super Scoop and the scow collided. He sued Dutra under the Jones Act, alleging that he was a seaman injured by Dutra's negligence, and under §5(b) of the Longshore and Harbor Workers' Compensation Act (LHWCA), 33 U. S. C. §905(b), which authorizes covered employees to sue a "vessel" owner as a third party for an injury caused by the owner's negligence. The District Court granted Dutra summary judgment on the Jones Act claim, and the First Circuit affirmed. On remand, the District Court granted Dutra summary judgment on the LHWCA claim. In affirming, the First Circuit noted that Dutra had conceded that the Super Scoop was a "vessel" under §905(b), but found that Dutra's alleged negligence had been committed in its capacity as an employer and not as the vessel's owner.

Held: A dredge is a "vessel" under the LHWCA. Pp. 4-15.

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