On Sep 30, 1:24*pm, Clive George wrote:

Trouble is it needs the connection to the ground that a boat doesn't
have, so having a sailing background will naturally confuse things.

I disagree. Whether the vehicle is a boat or land vehicle it exploits
the energy available at the wind/surface interface. In the case of a
boat the keel just acts as a wing underwater while the sail acts as a
wing sticking up in the air. We know there are sailboats that can
tack their way downwind much faster than the wind, so all we need to
do is connect two such boats side-by-side with a long telescoping
pole. Now they can go downwind staying on alternate tacks and the
whole contraption constitutes a "boat" that goes directly downwind
faster than the wind.