I guess once people got the idea of fluid movement around restrictions
creating usable pressure differentials, it became just a matter of
experimenting with different shapes and fluids.

When you say "experimenting with different fluids" do you
mean like sulfur dioxide? Does it increase or decrease the
efficiency of sails?




Think of this. The sail has the most power delivered to it when the
residual wind velocity is zero after interacting with the sail.


I think that's a mistaken assumption. The sail has the most
power delivered to it when it is developing max differential
pressure theoretically possible for it's density & initial
velocity.



The most efficient sail design reuses the wind velocity, similar to the
stages on a turbine engine.


True. That's why the America's Cup racers all have to be
limited by rule as for how many masts they can rig. It got
to be a PITA inventing new terms for the fifteenth &
sixteenth mizzen.


The most efficient sail design of all time was developed in Northern
Italy. The design was lost during the early Renaissance, only to be
recently uncovered during and archeological dig in a shallow bay. The
sails reused the wind many times over with each "stage" adjusted for the
reduced wind velocity. The sails are a series of "slats" with multiple
gaps and adjustable angles of attack. They are referred to as Venetian
Sails.


Now that was a very illuminating little essay



Scout wrote:
One would think that the sheer volume of air would make its efficient use a
non-issue. Unless the point is the area of the cross-section of air
available to a given size boat is limited. If that makes any sense.

Congrats, you've re-invented the term "sail area"

Fresh Breezes- Doug King