Chuck wrote:
"If the water path from the surface of the Dynaplate is vertical (four
feet) does that mean return currents must travel along four additional
feet of seawater (at the hull-water interface)---?

Maybe, but there is a lot of area in that path. The hull-water interface
includes the entire submerged surface of the hull. It has been assumed
in this thread that the sail-boat hull is fiberglass, an insulator. The
impedance of fiberglass is vastly different from that of seawater.

The great mismatch between fiberglass and seawater means a radio wave
traveling along one of the surfaces won`t be readily absorbed into the
other.

Dynaplate is a name given copperfoil on a roll. Dynaplate is also a name
given a copper plate which has been etched to increase surface area
thereby increasing its contact area with water.

The surface of seawater contacting a boat hull is continuous with the
horizontal surface of the sea.

Vertical polarization is effective over seawater. Horizontal
polarization is ineffective. The sea short-circuits the voltage wave.

A horizontal wire can produce vertically polarized radiation. The
Beverage antenna works over poor soil. On page 720 of Kraus` 3rd
edition of "Antennas" is the "Flush Disc" antenna which produces
vertically polarized radiation over a highly conductive surface. It`s a
radiator in a pit and should be useful in a vessel.

Best regards, Richard Harrison, KB5WZI