This is to paraphrase anothe skipper who imparted this advise in another thread.
Draw a 40nm radius circle around your mission area with the star at the centre, patrol within there for atleast 48hrs. it was suggested that the max rangeis 50nm so leave teh outer 10nm for chasing strays that may escape from any attacks that you prosecute.
Hope this helps, good luck and happy hunting.
PS kudos to the skipper whom I am paraphrasing