Finding ships is easy. All you need to do is set up an extensive network of buoys, and then triangulate wave patterns.
Yeah right. And you can provide an example of such a network and where it has been tested? For the sake of discussion supposed I mapped out this network of buoys and deployed my own counter buoys to broadcast false data to whatever stations you had in place to gather these wave patterns?
Or suppose I just jammed your data links? Or finally suppose I just sank your buoys every time one was encountered? Soon you would have big gaps in your buoy network.
You can do better than that.