For hundreds of years before the dawn of steam power in the mid-1800s, ships moved across the world's oceans by wind power. Today, engineers in Germany are harnessing the wind again, combining age-old propulsion principles with 21st century technology.

The Beluga Group (Bremen, Germany) is in the process of equipping a new cargo ship with a large kite that will act as an environmentally friendly propulsion system. The SkySail consists of a large towing kite similar to a paraglider that is navigated by a fully automatic control pod and connected to the ship by a tow rope. It will be used offshore, when wind conditions allow, in addition to the ship's traditional engine.

"Using this new technology, ships can save on fuel costs and at the same time avoid extraordinarily high amounts of climate-damaging emissions," says Niels Stolbergs, managing partner of the Beluga Group. With the rising cost of oil, "the technology is ready at exactly at the right time," he points out. "Furthermore, significantly tightened emission regulations, through which increasing costs will accrue, are being put into place.

"Offshore wind energy is an unbeatable, cost-effective propulsion source available in large quantities, and we expect to gain a considerable competitive advantage by using the SkySail system," adds Stolbergs. "The system will revolutionize the shipping industry."

SkySails (Hamburg) spent 5 years developing the wind-powered system, which is expected to enter service next year. According to SkySails managing partner Stephan Wrage, virtually any cargo ship can be retrofitted with the technology. Depending on wind conditions, annual average fuel costs can be lowered 10 percent to 35 percent per ship. "Under optimal wind conditions, fuel consumption can be reduced up to 50 percent," he points out.

The towing kite will be manufactured with high-strength, weatherproof textiles. Sizes will range from 160 square meters to 5,000 square meters. "The profile of the kite is designed so that optimal aerodynamic efficiency can be achieved at any wind speed," explains Wrage.

The mechanical control actuators, as well as the electrical system, are installed inside the control pod, which forms the physical link between the kite and the tow rope. The control pod operates like the autopilot system of an airplane. Throughout takeoff, flight and landing, the autopilot controls the kite and a winch located at the bow of a ship. Data is collected via sensors and processed by software that sends control orders.

"Operating the control pod is similar to piloting a paraglider," claims Wrage. "It ‘pulls' to the left and right of the control chords. The aerodynamic profile of the towing kite is thereby modified and has an impact on the flight path."

The kite will be able to operate at altitudes of 100 to 500 meters, where strong, stable winds prevail. "At an altitude of 100 meters, the average wind speed is 10 percent to 20 percent higher than at an altitude of 10 meters, due to the absence of resistance from the surfaces of earth and water," says Wrage.