Motor Minesweeper = raumboot, but there was no 15 and 18 R-Flottillen. Text must say 15 and 18 M-bootflottilen. They really have fishing vessels.
Mine-detonating vessel = Sperrbrecher
It seems like only ships of 13 and 18 MS-Flottilen worked in sea. Boats M.1801-1805, M.1807, M.1304 and 5 others ships. They reported only: 15.34, 4 Hampdens flies by one kurs E. Our place is qu. 6989. Coordinates of minesweeping was ca. from 53.42.3 east to 53.43,2 east along 72 grad north.
Kommandant im Abschnitt Helgoland reported 5 various planes detected near island in 15.26-18.20. Last one was perhaps german fighter from Wangerooge.