I suspect a reasonably good sonar package could detect a standard cruising surface ship at distances up to and over 50 nm. A modern Mk48 is good for about 25-30nm. It would never be fired at the maximum range as a ship would hear the torpedo as soon as it was launched and high tail it the other way. To effectively be in the no escape zone, a ship needs to be about 10-15 nm away at most. A torpedo is still a close in weapon.
Ghost shark style drones will never be used to follow a ship, they will be positioned to intercept, mostly from information passed to them from another source, potentially several days beforehand. Ghost Shark manages its slow speed via large numbers prepositioned in an operational area
The Anduril Copperhead torpedo operates a little different to the Mk48. It is in effect a small loitering drone. It can be sent out on independent recon, and then activate in torpedo mode a substantial distance/time from the Ghost Shark itself. A Ghost Shark could send one or multiple out ahead of an intercept point, which then wait in silence and go live when the target is close.
