Sparky summed it up. Floating buildings are covered in 553.
553.8(D) Grounding Electrode Conductor Connection. The grounding terminal in the service equipment shall be grounded by connection through an insulated grounding electrode conductor to a grounding electrode on shore.
Handbook commentary
Grounding of electrical and nonelectrical parts must be connected to a grounding bus at the building panelboard. An equipment grounding conductor must be included in the feeder supplying the building and connected to the grounding terminal at the service equipment. For conductor sizes 6 AWG and smaller, the equipment grounding conductor must be provided with green insulation or green insulation with a yellow tracer. An insulated grounding electrode conductor must be installed between the service equipment and the grounding electrode on shore.
