During cruise MSM41 of the German research vessel Maria S. Merian in April 2015 a visual ship based survey was conducted on the composition and density of natural and anthropogenic flotsam in the Sargasso Sea (subtropical NW Atlantic). On transits between the regular stations of the cruise, flotsam was quantified on transects of 10 m width and lengths of 9.1 - 25.5 km. Start and end coordinates were determined from a handheld GPS. This dataset summarizes the metadata of this survey, including the time, coordinates of start and end point of the transects, as well as distance and area covered. Additionally, results are presented as densities of floating marine debris and pelagic Sargassum given in total numbers per transect and standardized to items km-2. The speed of the vessel was recorded from the handheld GPS for 2-7 times per transect in irregular intervals to estimate the average vessel speed during the observations.