Kite power for progressive freight transport

At first glance the freighter belonging to the Beluga shipping company moored in Bremen harbor looks just like any other vessel. The next stop for the "Beluga SkySails" is Venezuela. To help get it there it has special equipment on board. The ships' bow conceals a clever new propulsion system which only springs into action once out on the open seas.

After reaching the open waters, a 14-meter-long telescopic pole extends with a massive sail attached to the end. The 160 square meters towing kite quickly unfurls before soaring skywards, a procedure which takes between 10 and 20 minutes. The energy source which helps the kite reduce the freighter's diesel consumption by up to 35 percent per year is free and found in abundance on the high seas: wind.

Maiden commercial voyage

For six years engineers at the SkySails company, headquartered in Hamburg, have been busy developing the system which is now ready for commercial use. DHL Global Forwarding is also involved in the project. The logistics company has chartered "Beluga SkySails" to transport parts of a chipboard factory to South America.

The heart of the system has little in common with a traditional sail, even though both use wind power. The towing kite is more like a gigantic paraglider or parachute. The surface area covers up to 600 square meters, making it more than 100 times the size of a traditional parachute. The large size is necessary to pull a gigantic cargo ship weighing several tons.

A computer as pilot

The towing kite is made from weatherproof and highly robust textiles and is built to double thickness. Ropes attached to the kite merge into the control pod positioned immediately below it. The yellow watertight case is part of the control system and is fitted with a whole range of high-tech equipment, including the pod computer which processes signals from various sensors and controls a number of small motors also housed in the case.

With the help of these motors the pod is able to perform the same function as that of a paragliding pilot: It controls the kite. The length of the ropes to the left and right of the kite are adjusted, enabling it to be flown dynamically. This means that it can perform flight maneuvers such as a figure eight and so increase the tractive force of the kite.

High-tech tether

A tear-proof plastic tether leads down from the control pod to the winch and the so-called force transmission point. Both are mounted securely on the cargo ship. The winch acts as a rope memory device and regulates the length of the towing rope. The force transmission point is the point at which the tether is connected to the ship. Here the tractive force of the kite is transmitted to the vessel.

The interior of the tether also houses a special cable used to supply power to the control pod and transmit data to the second element of the control system, the SkySails-computer on the ships bridge.

Autopilot and weather routing

The computer has a graphical user interface and an autopilot which allows the towing kite to track the wind. The status of the advanced propulsion system can be checked on the computer at any time and flight, start and landing maneuvers can be introduced manually.

SkySails also offers optional weather routing for the system. The software is able to calculate the best route with the greatest cost saving based on meteorological data and shipping company's details (such as arrival time). The captain receives the recommended route translated into waypoints and can then steer accordingly.

The SkySails system offers a number of advantages. Hybrid cargo ships, such as the "Beluga SkySails" reduce the load on the main engine, which increases its operational life. They also use less fuel. Between 10 and 35 percent can be saved each year depending on prevailing wind conditions. Where less diesel is consumed, there are also fewer emissions, thus reducing the carbon footprint.

Good for the environment, the coffers and the crew

In comparison to the traditional sail the towing kite system uses stronger and more constant wind since it operates at heights of between 100 and 300 meters. The crew also does not have to contend with the boat tilting in high winds, or "heeling" as it is known in shipping parlance: there is no mast, which for a traditional sail acts as the lifting arm. And the "Beluga SkySails" team has something else to be thankful for: the kite smooths the hull's passage as it rides the waves. This also makes for greater ship stability at sea.

It pays for itself

The investment needed to convert a ship - and just about any cargo ship could be fitted with the system - pays for itself within three to five years. SkySails so far offers three systems which provide effective tractive power (at a speed of ten knots, 25 knots wind speed, dynamic flight and a wind direction of 130 degrees) of eight to 32 tons. Depending on the ship, the effective tractive power of eight tons corresponds, for example, to some 600 to 1000 kilowatts of engine output.

By 2010 the company also plans to offer systems with 64 tons of effective tractive power. Such a system would be capable of moving cruise ships across the seas.