Wind power is not a new concept. Windmills have been around for centuries, and wind-powered sailboats have been around for even longer -- since 3200 bce, or even earlier. The advent of engine-powered shipping relegated wind-powered boats to hobbyists, tourists and adventurers. But if the German company SkySails is right, we may soon see a return to shipping powered by the wind.

The notion is straightforward: a large parasail-type kite on a tow cable can add significant power to a standard diesel engine ship when lofted to 500 meters or so in the air. How much power? SkySails claims that a cargo ship can increase speed for a given fuel consumption by at least 10%, and often more; conversely, a sail-enabled ship can run at its standard speed but cut fuel consumption by as much as one-half. The technology is more efficient at capturing wind power than standard sails, takes up less shipboard space, and supposedly does not require additional crew. Navigational software linked to real-time weather data routes for optimal wind speed and travel time. The design has won a number of German innovation awards, but has not yet been field-tested in its full configuration (at least as far as I can tell); SkySails proposes that the design would work not just for commercial vessels, but for ships of all types.

If SkySails works, the benefits are more than reduced fuel cost or shipping time. The SkySails site claims that "the toxic emission volume of the world trade fleet equals that of the United States." A system (such as SkySails) which can cut fuel consumption and reduce travel time would in turn reduce those emissions.

While there is something superficially absurd about massive cargo ships being pulled along by kites, upon reflection the notion makes sense. It's a novel form of "hybrid" power, taking advantage of strengths of diverse propulsion systems: the consistency of diesel engines and the free availability and startling strength of wind power. While SkySails still needs to demonstrate that their system works as claimed, we will undoubtedly see more of these "situational hybrid" power generation systems in years to come.

This looks like a neat re-use of an old concept. A quick look at their website suggests they have run successful tests with smaller prototypes ( http://skysails.info/index.php?id=10&tx_mininews_pi1[showUid]=50&cHash=625fa68cc5 ).
Still, I'm not sure if this technology will catch on with major shipping companies, since shipping is quite a risk averse business sector.
And still, their ambitions are quite small (supplying 1% of the global cargo fleet by 2010), so in the end, the contribution to emissions reduction won't be that spectacular. But then, a drop in the ocean is still a drop.

Posted by: Lorenzo on December 8, 2004 11:15 AM

For this to work well, hulls would have to be redesigned with keels. Essentially the artists depiction is inaccurate - if the sail was at that angle the boat would no longer be moving straight through the water, which is what it was designed for.

I admit I didn't look at the whole site. But I see it only being useful to go almost straight downwind. Which is still worthwhile perhaps.

Posted by: Eric on December 8, 2004 4:37 PM

OK I dug around the site and the function is described here:

http://skysails.info/index.php?id=128

For this to happen the kite would need a full-on autopilot capable of maintaining the correct moment.

That's a very advanced kite, needing lots of sensors and lots of controls. Remember it has to pull in exactly one direction, relative to the wind and the water. Finding that stable state in anything except straight downwind is pretty difficult I think. I'd be impressed if it worked.

Posted by: Eric on December 8, 2004 4:55 PM

Eric, I think the artists impression shows the kite making an "8" movement. It's designed to do that. (Anyone who's ever flown a kite knows the movement). And that's how the thing maintains the correct moment.

Posted by: Lorenzo on December 8, 2004 5:05 PM

I doubt that the lack of a keel on the ship would pose a huge problem.  Even if the kite cannot be made to pull directly in the direction of travel, a bit of leeway can be compensated for by aiming the ship slightly upwind.

Yes, I have no doubt that ships deal with drift all the time; how do you think they compensate for ocean currents?  The same GPS autopilot that keeps the boat on course through the eddies and gyres and crosswinds will handle off-axis pull from a kite just fine.

Posted by: Engineer-Poet on December 9, 2004 6:28 AM