Dorus Rijkers
Bremer, Jan.  the chapter: 'Dorus Rijkers (1847-1928); Koning der Blauwe zeeridders' in 'Roeiredders aan het Marsdiep 1824-1923'; Nationaal Reddingmuseum Dorus Rijkers and the Helderse Historische Vereniging, Den Helder; November 1998, . pp. 111–140.  This book forms is volume 9 of the series: Helderse Historische Reeks. (Jan T. Bremer is a well-informed, serious author on especially historical/geographical matters about the Noordkop (the region around Den Helder in The Netherlands).