[desirableroasted]

You mentioned 600nm... at that far out, even the tiniest deviation will mean you and the target will never meet. And since the contact information is vague ("West" for example, can be a heading of 259 to 281; "Slow" is 4 to 6 knts), deviation is built in from the start. Moreover, the ship will probably change course along the way.

I disregard any contact reports further than 100nm, and even those I think about carefully. If it is a single ship moving away from me, I am not going to burn fuel hoping to overtake it AND find it. If it's a convoy 60 nm away, though, it's worth the effort to overtake.

Of course, stuff moving toward me or laterally is worth investigating.