Whakaotihia te rerenga e whai ake nei: I whanau a Cort Sivertsen i Brevik, Norway, te tama a te kaipuke. I te tekau ma rima o ona tau ka uru ia ki te ope moana o Netherlands; i te tau 1639 i whawhai ia i raro i te Lieutenant-Admiral Maarten Tromp i te
Te Pakanga o te Downs. I te tau 1642 ko ia te rangatira tuatahi i runga i te "Grote St. Joris", he kaipuke Dutch i utua e te ope o Venice hei "San Giorgio Grande". I huaina a Sivertsen ko "Adelborst" i tenei wa, he ingoa Dutch te tikanga "cadet". I te tau 1645 ka riro ia hei rangatira mo te "San Giorgio" ka uru ki te ratonga Venetian katoa. I te tau 1650 ka waiho te "San Giorgio" hei rangatira, a ko Sivertsen te rangatira rangatira. I roto i te mahi ki te kaipuke Turiki i te 13 o Mei 1654 tata ki te Dardanelles i pakaru ia me tana kaipuke i te raina o nga galleys Turiki, a ka totohu tekau ma rima o ratou; i te ra i muri mai ka tuku te hoia Tiamana o Tenedos ki a ia. Mo tenei i whakawhiwhia ia ki te Order o Saint Mark; i whakawhiwhia e te senate Venetian ki a ia me te tau 1400 o nga ducats koura. I te tau 1660 ka whakawhiwhia ia ki a Vice-Admiral.