"Bob Crantz" wrote in message
news
The mooring is tied to a conducting chain which is anchored into the
earth.

But the boat is insulated from the chain by a rope painter. Fresh water is
moderately conductive, but not nearly as much as brine. If you have a
ground "shoe" on the outside of the hull below the waterline, the current
will be directed through it into the water and then to the Earth.

A dock boat is usually tied with insulating lines to a wooden dock.

See above.

It's easier to pump excess charge by electrostatic induction to the moored
boat as the earth has virtually unlimited available charge and there is a
conduction path to the mast or boat. The docked boat can only redistribute
the charge available on the hull or polarize to the external field.

See above. Most boats are grounded to the water. Or they should be.

Max