As a former fighter pilot and an enthusiastic sailor for long time, I retired early in order to be able to spend more time sailing. While sailing a lot, I discovered that there are a lot of similarities between flying and sailing, such as driving a machine on fluids, no brakes, windage effects on the bow / stern, the propeller walk, navigation, etc., However, the most and remarkable similarity between airplanes and boats is the use of lift force.
Airplanes use lift force, created on the wing due to the air flow around it, in order to hold the airplane up in the air. Sailing boats use the lift force, created on the sails due to the same airflow around the sails, as their driving force.
There were always the questions of why do we still sail around with inefficient rigs, all bound up with complex rigging and high compression loads? Why do we try to make the sails look like wings rather than using the wing itself? Why do we use sails, although it is very well known that wings have a higher lift/drag ratio than sails, and therefore, can provide more driving force to the boat? Why do we use sails when wing's working angle of attack is smaller than that of a sail, and consequently, enables pointing higher?
I found that the answer to all these questions was not the theory of aerodynamics. It was the availability of the right technology!! There was no efficient wing, with a simple structure, easy to use, reliable, light weight, inexpensive, and good for all sailors in any weather condition. This is where I decided to go into it, and to try to develop a wing sail that meets these demands.
As usual, there are always trade-offs and compromise, as well as several different approaches to solving a problem.
The first approach is the hard (rigid) wing. This type of a wing sail is the closest to aircraft wing. It is aerodynamically efficient, has higher aspect ratio and performance with relatively small sail area. The trade-offs are: it has a complex structure in order to enable variable geometry. It is not reefable. It cannot be folded down. It does not have enough sail area in running down wind, and it is very expensive. Hard wing sails are very efficient for extreme speed sailing, for racers and professional sailors, and for other exotic uses.
The second approach is the soft wing sail. This wing sail is made of sail cloth. It can be hoisted, reefed and folded exactly like a main sail. It is not limited in size. It is easy to handle and is as simple as any main sail, with no complex mechanics and no "tail" rudders. The wing turns and wind vanes spontaneously, uncomplicated variable camber system (done by changing the angle between the mast and the boom), no hinges, trailing edge twists naturally, no moving parts, no problems on anchor or in the marina, and it is relatively inexpensive. The trade- offs are: Soft wing sails are less aerodynamically efficient. They need bigger sail area (good for downwind), and one has to hoist and fold it and to keep on with handling sails and sail cloth.
Soft wing sails are good for cruisers and cruiser / racers, and are suitable and robust for recreational service.
I truly believe that wings (of all kinds) are the next step in the evolution of sails.