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Why wing Sails
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, the effects of the wind, 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 was always the question 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 and don't use wings? 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 a wing's working angle of attack is smaller than the sail angle, and therefore, can point higher?
I found that the answer was technology!! The main problem was not the theory. It was the question of how to make an 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 find a technical solution and to develop such a wing sail.
As usual, development means trade offs and compromises, and there are 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 very aerodynamically efficient, has a better aspect ratio and, very high performance with relatively small sail area. The trade offs are: it has to be a complex structure to enable variable geometry of the wing's camber (flaps), it is not reefable, it can not be taken down and folded, it does not have enough sail area in running down wind, and, it is very expensive. Hard wing sails are very good for extreme speed sailing, for racers and professional sailors, and for other exotic uses. Also, small boats like C class and A class catamarans that have relatively small wings, can benefit from the advantages of hard wing sails.
The second approach is the soft wing sail. This wing sail is made of sail cloth, and if designed properly, it can be hoisted, reefed and folded exactly like a main sail. It is not limited in size, it is easy to handle, simple as any main sail, no complex mechanics, no "tail" rudders, the wing turns and wind vanes spontaneously, simple variable camber (in "Omer" wing sail it is done by changing the angle between the mast and the boom), no hinges, trailing edge twists spontaneously (no need for internal twisting carbon spars), no moving parts, no problems on anchor or in the marina, and, it is relatively inexpensive. The trade offs: Soft wing sails are less aerodynamically efficient than hard wing sails, therefore, they need more sail area (good for down wind), 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.
It is not any more a question of whether wing sails are more efficient than sails. They are!
The questions should be now: what is the right wing sail for a specific use, what is the right wing for a specific sailor, is the wing well designed for it's purpose and, which kind of wing sail is the most cost effective.
Ilan Gonen
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