 In 1972–73, he began working as a researcher with the Nederlandse Organisatie voor Zuiver Wetenschappelijk Onderzoek on Dutch-Asiatic Shipping.In 1973–74, he taught history in Haarlem, then in March 1974, the University of Leiden appointed him as a university docent.In 2004, he succeeded Jaap R. Bruijn, as Professor of Maritime History.