Already at the age of ten, in 1652, Cornelis sailed on his father's ship. He became privateer in 1665 during the Second Anglo-Dutch War and was captured by the English on 15 April of that year when his force of two ships was defeated by three English vessels, among them the "Diamond" and the "Yarmouth". His crew had to bodily restrain him to prevent him from blowing up his ship, the "Eendragt" of 32 cannon. Because of his famous father and uncle he was considered worthy of royal interest. During interrogation the brother of the king, "Lord High Admiral" James, the Duke of York, inquired about a bullet hole in the top of Cornelis's hat, asking the captain to excuse the English for having damaged his clothing. Cornelis grumpily answered that he was proud of the hole; only he would have preferred it to have been a bit lower, to now being a prisoner.