By Steve Rosenberg BBC News, Bremerhaven, northern Germany

Ms Beluga is now on its way to Guanta in Venezuela Kite in action

Ten thousand tonnes of metal heaving through the water, the ship's giant masts glistening in the winter sun.

But there is something even more magical about being aboard MS Beluga SkySails.

On the face of it, this vessel - which is carrying parts of a timber production line to Venezuela - looks like any other cargo ship.

In recent months, commercial shipping has been criticised for not doing enough to tackle global warming. Of all the CO2 being pumped into the atmosphere today, 4% comes from ships. That's more than the aviation industry, primarily because 90% of global trade is done by sea.

MS Beluga SkySails believes it has a solution. It has set sail on a mission to turn the oceans green.

Once the ship has reached the open sea, it reveals its brand new weapon in the fight against global warming: a kite.

Twisted spaghetti

The 160sq m (1,722sq ft) blue-and-white kite is winched up a mast, strings dangling like twisted spaghetti.

We can demonstrate that you can combine economy and ecology Verena Frank, Beluga Shipping

For half-an-hour or so, it sits there at the top of the mast, not doing a great deal.

Wind power is a wonderful thing, but you do actually need some wind to make it all work - and there is not very much at this particular moment.

Half-an-hour later, though, the wind has picked up and the kite is flying hundreds of metres in the air - and helping to tug the ship along.

Kite power means the ship's engines down below can work on reduced power: and that means fewer carbon emissions.

It also means smaller fuel bills. With the price of shipping fuel having doubled in the past two years, kite power is promising big savings.

MS Beluga SkySails believes its fuel bill will be cut by £800 ($1,560) a day.

"We can demonstrate that you can combine economy and ecology," Verena Frank of Beluga Shipping explains.

"Economy, because you can reduce fuel consumption and fuel costs, and on the ecological side of things, we reduce emissions."

Magic wears off

The kite is controlled by computers. One computer helps it to fly in figures of eight in the sky - maximising the power it produces. Another computer adjusts the kite's direction.

If the project is successful, expect to see even bigger kites soon - some up to 5,000sq m (53,820sq ft) in size pulling ships across the seas and oceans.

After several hours on board the ship, the magic starts to wear off.

The sun has gone down, it is freezing cold. To warm myself up I start thinking of the ship's final destination - Venezuela.

But I will not be seeing the South American sun. By the evening, the ship has returned to chilly Bremerhaven to drop off the journalists, before setting sail - again - on its transatlantic journey.

HOW THE KITE SHIP WORKS The kite sail will help reduce annual fuel costs by 10-35%. Reduced fuel also means fewer harmful carbon emissions The large towing kite resembles a paraglider and is shaped like an aircraft wing, to enable it to take advantage of different wind directions It operates at 100-300m above surface level - much higher than a normal sailing craft - where winds are stronger and more stable The kite can be used in winds of 12-74km/h (7-40 knots) and not just when the wind is blowing directly from behind the ship