Cargo ships propelled by giant kites

German company SkySails are developing wind propulsion systems for modern shipping. These systems are large kites similar to those you see powering kite surfers. Their target market includes cargo ships and large motor yachts.

The advantages of the kite system are that it can be flown in clean air well above the surface of the water and because it is tethered to the deck of the ship it doesn’t produce the leaning moment that would be experienced with a similar size sail on a mast.
The planned product range contains towing kite propulsion systems with a of up to 5,000 kW (about 6,800 HP). On annual average fuel costs can be lowered between 10-35% depending on actual wind conditions and actual time deployed. Under optimal wind conditions, fuel consumptions can temporarily be reduced up to 50%.

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6 Responses

  1. An interesting article on the sailing ships of the past in the Sydney Morning Herald:
    http://www.smh.com.au/news/national/the-future-is-just-plain-sailing/2007/05/04/1177788404539.html
    Sailing ships may once again ply their trade around the world.

  2. The kite idea is fine for tail winds but nowhere have I found any comment or article on just how far off from dead astern the wind can be and still provide useful forward motion to the ship. The closest was a general comment that it will work with winds coming from the side but there was no attempt to quantify what ‘coming from the side’ means. My guess is that the useful wind direction range is no more than 30º either side of the ship’s centreline.
    Some thoughts anyone?

  3. Peter,

    My sailing experience tells me that this would work from a fine reach to straight downwind. i.e. the wind is blowing anywhere from slightly forward of the ships beam to over the stern. Best performance, similar to sailing should occur when the wind is at about 90 degrees to the direction of travel (reach).

    The idea will be to control the kite so it forms an aerofoil that pulls the ship forward. To do this I suspect they rotate the kite so it forms the aerofoil when the wind is coming side on and the kite naturally positions itself for best efficiency by always trying to swing around in front of the ship.

    The result will be a thrust vector that has one component in the direction of ship travel and another, hopefully much smaller component, at 90 degrees to the ship centerline. There will be some pull sideways but if they’ve designed it well that will be small compared to the pull forward.

    Maybe there are some kite surfers out there that can provide more insight.

    Luke

  4. Luke,

    In principle I agree with what you say however from some basic arithmentic I’ve done concerning kite theory and applying it to the shipping application, I’m of the opinion that even though it will work with the wind abeam, despite this being probably the most flight efficient situation from the kite’s point of view, the useful forward acting force is really quite low and from the ship’s point of view, probably not worthwhile. If you are interested I could send you my workings but would have to know your email address.

    With regard to kite surfers, from having watched them in action I have to conclude their useage is not comparable with that of a ship. A tongue in cheek observation;- kite surfers don’t really want to go anywhere. Even the best of them seem unable to actually make any headway into the wind and gradually lose ground. There’s little fun in just running with the wind and besides, having done so requires a long walk back to the starting point. Because of this they tend mainly to concentrate on alternate reaching from side to side with only a short walk/swim back to base after a half hour’s sailing.

    I stand to be corrected.

    Peter.

  5. Hope will be a giant leap towards sustainable development. Huge amount of Fuel will be saved.

    Vaibhav Satpute
    India

  6. Regarding windsurfers, I have seen a few in action too. On one occasion, at a kite festival. The commentator at one point mentioned that the windsurfers needed another 5 knots of wind speed to make progress upwind. However, these guys were some of the best in town (Adelaide, SA) so perhaps average windsurfers struggle in this area!

    Regarding ships, my feeling is that even a very small percentage of full kite thrust would still equate to significant $ saving, due to the large $ involved…

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