I have found that Ahrens families are mostly from the Rostock area of Mecklenberg.
If you are not positive that your ancestor actually resided in Holland, then maybe he migrated across country from Mecklenberg to Holland where he signed on to a ship ?
If you check the German telephone directory You will find a dozen Ahrens, listed under Rostock.
I am researching children or siblings of - Joachim Christoph Ahrens, born about 1800 in Rostock, Mecklenberg area. He had a son: Christoph Johann Heinrich Ahrens Born: 14 September 1835 at Klein Upahl, Schwerin, Mecklenburg. Buried: possibly Tanunda, South Australia
If you see any link to your ancestor, please let me know.