Dr. De Boer says that "he was a problematic character from beginning to end", and was frequently exchanged in sources with Jacque Forant. He served the Admiralty of Amsterdam. In 1638, he fought with great courage, under Tromp, at Dunkirk. Right after this, he was in trouble with Witte de With, who seemed to have trouble, during this period, with many men. He left the fleet without authorization and then gave untrue reports about his activities. He received a heavy fine and was suspended. At the Battle of the Downs, Robbert Post was in Voorns' ship, the Deventer. In 1645, he worked at the Admiralty of Amsterdam. In 1647, he was assigned to Witte De With's squadron to relieve Brazil, but he died on the voyage on 5 August 1648. He had commanded the Amsterdam ship Huis van Nassau (40 guns). On 15 March 1651, his widow requested payment of pay due to him.