once the transformer is installed, and the output PE connected to the anodes (Zincs), that couples the transformer output PE to the dockside PE THROUGH the CONDUCTIVITY of the water.
The input PE is connected to a terminal block, but that is not connected to anything else. It merely provides a secure anchor for the PE cable. it MAY, if a JUMPER is installed, be coupled to the output PE for when the yacht is hauled out. This should only be done by a qualified electrician, and removed before the yacht is re-launched. With the GFI’s in the circuit, this is an optional step that prevents potential shocks should someone touch the hull / anodes at the same time as an internal electrical fault occurs (extreme low probability).
Having 360V on the yacht is no big deal, as it is only accessible inside the protective case of the transformer. We had 415V 3 phase on our small 48’ yacht with no issues.