Come fly a kite!

September 25, 2007 6:23 AM

Sky Sailshas a new take on an old idea to save on fuel for marine shipping: kite sails. The twist? No new ships required.

Why this is a good idea: marine transport accounts for 4-5% of the world's carbon dioxide emissions. Putting sails on the existing commercial fleet would shave 1-2% off that. Not much? That's the equivalent of grounding at least half of all of the airplanes in the world.

There are a couple of American companies doing this too: Kite for Sail and KiteShip, but neither seem to be as advanced as the Germans.

posted by bonehead (14 comments total)

This is very cool.

I never understood why zeppelins don't have sails. You're already floating in the air, why not use it for propulsion?
posted by Pastabagel at 6:48 AM on September 25, 2007

I think that's a little like asking why fish don't have watersails. Because they want to move independently of the water. (Also, the body of the zeppelin probably has plenty of sail-like action. Look at a hot air balloon.)
posted by DU at 6:57 AM on September 25, 2007

I never understood why zeppelins don't have sails. You're already floating in the air, why not use it for propulsion?

what?! Why would a zepplin need a sail? It's resting speed would be that of the air around it, like a balloon. The only time it would need propulsion is when it wants to move against the wind.
posted by delmoi at 7:01 AM on September 25, 2007

Is this an African or European Zeppelin? Anyway, Whole Lotta Love for wind power.
posted by Mister_A at 7:06 AM on September 25, 2007

I never understood why zeppelins don't have sails. You're already floating in the air, why not use it for propulsion?

The sail you see in the air is only half the story. You need an underwater sail as well (a keel) or the right hull shape. Sails exploit the flow differential in two different fluids. An airship is floating in one fluid (air), so sails will do them very little good.

Sails are fun on recreational boats, but efficient hull-shapes for sailing are not at all similar to efficient hull shapes for cargo carrying.
posted by b1tr0t at 7:15 AM on September 25, 2007

And anyone who thinks these kits are a good idea has never tried to manage a simple spinnaker in rough conditions.
posted by b1tr0t at 7:17 AM on September 25, 2007

These days, b1tr0t, we can see the bad weather coming and pull the sails in, when we = the captain and crew of a large ocean-going freighter. I imagine there's an emergency release to cut the cable too.
posted by Mister_A at 7:26 AM on September 25, 2007

These days, b1tr0t, we can see the bad weather coming and pull the sails in, when we = the captain and crew of a large ocean-going freighter. I imagine there's an emergency release to cut the cable too.

Indeed. I help crew a 19th century schooner (and former cod-fishing vessel), and while it's not especially fun, we can take in the sails when the weather goes bad, even with not much notice. Agreed that there's probably an emergency release (I HOPE anyway!), or at least someone willing to go out on deck with a good pair of clippers and make a release.
posted by kalimac at 7:34 AM on September 25, 2007

b1tr0t, it may be sub-optimal, but the carriers I know about get really excited over the possibility of saving even a few percent on their fuel bill. It's one of shipping's major costs. If the claimed 25% savings on a trans-Atlantic crossing works out, that's huge.
posted by bonehead at 7:45 AM on September 25, 2007

Putting sails on the existing commercial fleet would shave 1-2% off that.

Yeah but the melt of the arctic ice pack and the resulting new shipping lanes will save even more than that.
posted by Keith Talent at 8:27 AM on September 25, 2007

Um, not to be a downer or anything, but those photoshopped sails on freighters beg the question of how a kite at 90 degrees to the direction of travel attached to the bow of a boat would help the boat to go in the direction intended.

Not the balance point.
No keel.
Bad sailor, no spinnaker.
posted by lothar at 9:43 AM on September 25, 2007

Back in the late 70s or early 80s, there were a few Japanese sail-assisted cargo ships built with similar intentions and promises, IIRC. Little came of it.
posted by Western Infidels at 10:09 AM on September 25, 2007

...how a kite at 90 degrees to the direction of travel attached to the bow of a boat would help the boat to go in the direction intended.

From the February 26, 2005 New Scientist article, The New Age of Sail:

SkySail's aerofoil is designed to maximise thrust whatever the wind conditions. It uses a computer autopilot and patented wind sensors coupled to the ship's steering system to calculate the kite's optimum position. Then the autopilot manoeuvres the kite using motors in a control unit suspended beneath it to change the trim of the aerofoil by adjusting the tension in its control lines. The kite can move along a rail around the hull to maximise its towing efficiency and a winch on the ship adjusts the length of the kite's main line to fly it where the wind speed and direction are most favourable.
...
"One surprising result from the trials was the vessel's stability in heavy seas," Wrage says. Unlike conventional sails, the kite tends to stabilise the ship instead of making it heel over. This is partly because it is tethered to a rail close to the vessel's centre of gravity, and partly because the horizontal tug of the kite is counterbalanced by the vertical pull it generates, which tends to hold the vessel upright. "The sail acts like a damper so the ship moves smoothly, which will prevent passengers being sick." This is significant because Wrage sees cruise liners, and the growing number of cargo ships that carry passengers, as important markets for the technology.

However, I think the additional complexity of the sail system, extra crew (and training), installation and refitting costs, maintenance, and the availablity of decent winds in desired trade routes would make cargo ship sailing uneconomical. You're still going to need engines, and they replaced sails because they were faster, more reliable, and more dependable. If your cargo schedules are as fickle as the wind, so are your profits.

WRT to sails on dirigibles, they would certainly give the term 'going aloft' a whole new meaning.
posted by cenoxo at 1:35 PM on September 25, 2007

You're still going to need engines, and they replaced sails because they were faster, more reliable, and more dependable. If your cargo schedules are as fickle as the wind, so are your profits.

The SkySail people have thought about this. Since the ship always has its engines as an option -- the 'sail' is just supplementary -- you never have to worry about being stranded or even behind schedule. The worst-case scenario is that you don't get any free boost. Then they have a weather-prediction system that helps plot routes and tells you when to deploy the sail.

I expect from a captain's perspective it's not that much of a change. You plot your course, and you put the sail up and down when the software tells you to.

I do question the numbers that they're giving on their website, but that's just the usual marketing drivel. My suspicion is that they're basing the numbers off of a trip that lets you use the sail in both directions, while in most merchant routes (which tend to be back-and-forth), it seems like you'd probably only be able to use it part of the time. (Either all the time at reduced efficiency, because the wind is perpendicular to the route, or at max efficiency half the time, with wind parallel to the route.)

It's certainly interesting, and I'm glad that the high costs of fuel are starting to spur some innovation.
posted by Kadin2048 at 11:46 PM on September 25, 2007