You can assume "halved" crew numbers if the ship serves only policing duties and no combat role, partially due to different shift concepts. In return these ships tend to have rapid crew rotations, e.g. every two months for the Knud Rasmussens.
That gets you to crew numbers in the 40-70 range for these patrol ships, a bit dependent on armament and auxiliary equipment. For older ships, in particular before the mid-90s, you then also have to add a factor of up to around x2 for lack of automatisation.