As I recall from training many years ago, the shield is a noise remedy.
It seems it should connect to the vessel's signal ground /
counterpoise through a radio frequency capacitor, to cancel and block
noise from the radio circuits, via the ship's neutral connector. The
transformer case and frame should be connected to shoreside "Earth",
and neutral at the power pole / entrance.

This presumes that the shield is not connected to the frame of the
transformer. If it were, I would try it both sides and disconnected, to
satisfy noise and galvanic requirements while at the dock.