There's 2 different things being described in this thread.
One thing is the simultaneous turning that enemy ships do in SH4 when your sub is spotted. It lasts from the split second of detection to 20-30 minutes after the moment of last contact. It's AI controlled behavior that is the same in SH4 as it was in SH3, altho in SH4 it appears to be somewhat bugged. Having followed mod developments very closely for SH3, I've never seen anything about this AI routine that can be player modded, although in SH3 some of its more frustrating side effects (like ships bunching up and stopping) could be lessened a little bit by increasing the column distance in Random Groups.
The other thing that's being discussed in this thread is what the original poster asked about
: zigzagging, as it is known in naval doctrine, in which ships make somewhat minor course changes every so often (like, every half hour) while remaining on a base course toward their destination, staying in in column formation. This was SOP for pretty much every WWII navy.
There is no provision in the SH3 AI for zigzagging, as it's defined in the preceding paragraph. I've seen nothing in SH4 to make me think it's in there either, since under the hood they're 99% the same.
However...you can script zigzagging with waypoints. Lots and lots and lots of waypoints. It would work fine for creating a single mission, but for creating a campaign, it would make your brain explode. But don't let that stop anyone from trying
