In the mid-1940s, an innovation called “hang glider” was developed in the United States to improve the flight stability of small aircraft. A flap mounted at the end of a long lever that extended rearward behind the wing, maintained the angle of the wing during flight. The hang glider concept can be adapted to sailboats powered by an aero sail or aero style wing in place of a more traditional fabric sail.
Using traditional sails to propel a boat requires that each crew member be highly skilled to quickly readjust the sails in response to changing wind conditions and changes in the sailing direction of the vessel. Adding wind propulsion to modern ships offers potential reductions in fuel costs and ship exhaust emissions. Modern ship wind propulsion must provide high propulsive effort and be easy to operate, perhaps even without the ropes used to readjust the angles of the sails of ships. The requirement calls for a different design of the sail controlled by a different operating system.
Using wind power to maintain and adjust the angle of a wing-sail to the ship’s hull reduces the need for ropes and cables. Resetting the wing-to-sail angle to the hull requires the use of large, powerful electric motors to drive large worm gear mechanisms to reset the wing-to-sail angle. Using one or more smaller downstream wing-sails mounted on an extended length lever to adjust the angle between the hull and the upstream propulsion mainsail would require smaller electric (or hydraulic) motors. resulting in smaller worm gear mechanisms. Readjusting the hull / wing-sail angle would require less energy.
Sails and ships
Ships designed to carry different types of cargo would require different types of sails. A container ship needs the maximum available deck space to carry a payload, leaving the bow area installed and retractable kite sails as a possible option to aid propulsion along parallel sections of travel. with the prevailing trade winds. Due to the nature of the payload that needs to be carried below deck, bulk carriers can use the combination of bow mounted retractable kite sails as well as deck mounted masts for sail technology or for vertical axis wind turbines such as Magnus Rotors driving electric generators.
Increased propulsive force
The option of installing sail sails on masts that extend skyward from the deck can also allow a hybrid sail-to-sail configuration. On an aircraft accelerating along a runway, the upper wing profile allows the air to simultaneously accelerate to a higher speed while reducing the upper air pressure well below the surrounding air pressure. The difference between higher dynamic air pressure below and lower above produces lift. Likewise with a wing canopy installed above the deck of a sailing vessel, the difference between the higher dynamic air pressure on the upstream side and the lower side of the shade generates the propulsion.
Airplane wings will only develop lift under certain flight conditions and at certain flight speeds, otherwise the wing will stall with an increase in the upper dynamic air pressure of the wing. Likewise, depending on the design and angle of the wing, the shaded side of the wing may also experience a stall. Due to the flexibility of the weight of the wing on a ship’s deck, it becomes possible to incorporate a pair of vertical axis and counter-rotating rotors near the leading edge. On the downwind wing-sail side or shade side, the rotor boundary layer effect would direct rapid airflow into that area and maintain extremely low dynamic air pressure.
Designing wing sails to include rotating rotors at the leading edge allows the boundary layer effect of each rotor to redirect the wind flow through a severe angle. It is possible to install a small vertical axis wind turbine above each rotor to initiate the rotation, after which the wind-induced boundary layer effect would maintain the rotation of the rotor. A dual rotor system can allow extreme width at the leading edge of the wing-wing, placing its shadow or downstream side at such an extreme angle that only the rotating rotors could produce the necessary boundary layer contact and extremely low dynamic air pressure on the shadow side.
The wide leading edge of the wing sail combined with larger diameter rotors would allow the installation of extreme diameter main masts capable of withstanding extreme dynamic wind-induced shear load. Such installations would be compatible for freight vessels which require a high level of propulsive force and relatively low sailing speeds, compared to smaller passenger and pleasure sailing vessels which would navigate at higher speeds. For high speed wind sailing, a narrower leading edge with small diameter rotors would allow an optimal different wing sail angle to produce the required propulsive force at higher sailing speed.
Parallel sails downstream
When installing upper and lower wing flaps downstream behind the main flight wing of a free-wing aircraft, the versatility offered by the vertical-axis free-wing sail installed on a ship’s deck allows the application of downstream parallel wing flaps installed on the extension levers behind the main propulsion sails. In the neutral setting, the widely spaced placement of the parallel downstream wing flaps would extend beyond the width of the counter-rotating rollers, allowing them to operate in the wind current. When the steering mechanism is activated, a downstream wing flap would stay in the current of the wind.
To optimize the main propulsion wing angle setting, independent steering control would allow each of the downstream wing flaps to be set at a different angle, relative to the main propulsion wing. The widely spaced placement of the wing flaps downstream behind the main canopy would reduce obstacles to a rapid flow of air leaving the trailing edge of the propelling wing-wing and flowing behind it.
Here is a video showing how a free-wing canopy can propel a blow-kart along a beach:
The trade winds under sail
Sailing parallel to the trade winds, the retractable airborne kite sail would pick up the propellant energy of the more powerful winds that blow at a higher altitude over the ocean. The winged sails mounted on the deck would capture the propellant energy of the powerful cross winds that blow towards the ship at angles between 20 degrees and 120 degrees to the bow. Beyond 90 degrees from the bow, the airborne kite sails would assist the winged sails mounted on the deck and would do so exclusively when the wind direction moves beyond 120 degrees from the bow (60 degrees to the stern).
Free sail submerged
The combination of an available market for transportation service, high fuel cost, environmental considerations, proper water flow through narrow channels, and suitable locations to secure retaining cables for guide kinetic ferry ships. Such technology has long provided services on inland waterways. Further development of technology could introduce kinetic ferries to suitable, comparatively narrow inter-island ocean channels where the water current flows sufficiently quickly. Submerged free-wing sails could be developed to provide high propulsive force at low speeds for freight service or faster navigation with reduced propulsive force for passenger service.
There are several potentially suitable channels located internationally where further assessment is needed. Off the coast of the United Kingdom, narrow and shallow candidate canals can be found in the Outer Hebrides, Orkney Islands, Shetland Islands, Isles of Scilly and the Faroe Islands. There are a few narrow, shallow channels between the Philippine Islands where the current may be sufficient to maintain kinetic ferry service. At the southern end of South America, the ocean current sustains rapid waters between neighboring islands where a kinetic ferry service can be considered. In the Caribbean, the canal between Saint Kitts and Nevis would be a possible candidate.
While the idea of the hang glider has its origins in the aviation industry, the hang glider concept has the potential to be adapted to maritime sails, using aero sails in place of traditional fabric sails. The concept may even be applicable to wing sails which incorporate counter-rotating cylinders installed just behind the leading edge. It is said to have an overwater application on the decks of wind-powered ships, also under the hull to propel kinetic ferries driven by the water current. Modern wind-powered ships would sail with a variety of wind-powered technologies that will include airborne kite sail to navigate parallel to the trade winds.
The opinions expressed here are those of the author and not necessarily those of The Maritime Executive.