Wind assisted propulsion

Wind assisted propulsion is the practice of decreasing the fuel consumption of a merchant vessel through the use of sails or some other wind capture device. Sails used to be the primary means of propelling ships, but with the advent of the steam engine and the diesel engine, sails came to be used for recreational sailing only. In recent years with increasing fuel costs and an increased focus on reducing emissions, there has been increased interest in harnessing the power of the wind to propel commercial ships.

The mechanical means of converting the kinetic energy of the wind into thrust for a ship is the subject of much recent study. Where early ships designed primarily for sailing were designed around the sails that propelled them, commercial ships are now designed largely around the cargo that they carry, requiring a large clear deck and minimal overhead rigging in order to facilitate cargo handling. Another design consideration in designing a sail propulsion system for a commercial ship is that in order for it to be economically advantageous it cannot require a significantly larger crew to operate and it cannot compromise the stability of the ship. Taking into account these design criteria, three main concepts have emerged as the leading designs for wind assisted propulsion: the “Wing Sail Concept,” the “Kite Sail,” and the “Flettner Rotor.”

As a result of rising oil prices in the 1980s the US government commissioned a study on the economic feasibility of using wind assisted propulsion to reduce the fuel consumption of ships in the US Merchant Marine. This study considered five different designs and concluded that with current technology the design that offered the greatest benefit would be the “Wing Sail Concept.” The "Wing Sail Concept" would largely be an automated system of large rectangular solid sails supported by cylindrical masts. These would be symmetrical sails which would allow a minimal amount of handling to maintain the sail orientation for different wind angles, however this design was at the expense of increased efficiency. A small freighter was outfitted with this system to evaluate its actual fuel gains with the result that it was estimated to save between 15–25% of the vessel's fuel. Despite the positive findings of this study, the "Wing Sail Concept" failed to catch on and is not currently found on any commercial ships.

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