Kite rig
Wind propulsion using kites flown from control lines.
A kite rig is a wind-assisted propulsion system for vehicles, using kites flown from control lines rather than masts. It differs from conventional sails by drawing power from a kite that can be adjusted relative to the wind. Kite rigs are used for both recreational and commercial purposes on water, land, and snow.
Structure
Current kite rigs can be sailed within 50 degrees of the wind, enabling upwind travel by tacking. A power kite is held at an angle to the wind via control lines, generating lift and drag that pulls the vessel. The kite's pull combines with forces from the vehicle—such as water resistance or wheel friction—to move it. Windspeed increases with height, giving kites more thrust per unit area than conventional sails, with steadier, less turbulent winds aloft. Kites can be adjusted manually or automatically, but cannot stay aloft without wind and must be re-launched.
Applications
Kite rigs power recreational conveyances on water and land. On water, they drive surfboard-like boards in kitesurfing and boats in kiteboating. On land, kite landboarding uses similar power for skateboard-like boards. Over snow, kites propel snowboards or skis in snowkiting. Traction kites for solo sports typically have an area of 1-16 square meters; kites over about 5 square meters require expertise. Ship-pulling kites, reaching hundreds of square meters, need special attachment points, a launch and recovery system, and fly-by-wire controls. The SkySails propulsion system uses a large foil kite, an electronic control system, and an automatic retraction system. This kite, though 1-2 orders of magnitude larger, resembles arc kites used in kitesurfing but is inflatable rather than ram-air. A control pod replaces direct tension on multiple lines; only one line runs from ship to kite, with bridle lines from kite to pod. Power and commands travel via cables embedded in that line. Launch and recovery use an animated mast that grips the kite's leading edge, also inflating and deflating it; when not in use, mast and deflated kite fold away. The commercial cargo ship MS Beluga Skysails, launched in 2007, supplemented conventional propulsion with a kite rig. A European Union-funded four-year study using that ship reported 5% overall fuel savings, translating to 530 t of CO2 per typical year. The study estimated that 25,000 similarly equipped ships could reduce fuel consumption by 5.6-8.1 Mt and save 170-25 Mt of CO2 and 45-65 kt of NOx. On its maiden voyage, the ship saved 10-15% fuel, $1,000 to $1,500 per day while the kite was used. The fishing trawler Maartje Theadora was retrofitted with a kite rig in 2010.
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