I see there's some confusion regarding the technology.
1. These kites are not "small", unless you think 5000 square metres is "small".
2. These kites fly at altitudes of hundreds of metres, there were ordinary rigs never get; at these altitudes, winds are far more stable and far stronger than at 50 metres altitude
3. Power from a kite increases with surface area and windspeed by the square: at 1000 metres altitude midlatitude winds, a 5000m² kite delivers tremendous power. The bigger skysails will go up to delivering 6,800 HP nominal power. Quite impressive if you ask me.
4. with the kite, there's minimal to no heel (in contrast to ordinary rigs)
5. Courses up to 50degrees to the wind still work with a skysail, never with an ordinary rig
6. The skysail can make the typical "8" movement, as anyone who has ever used a kite knows, this is were you get constant power from. This is impossible with an ordinary rig.
Etc...
Everything works automated, with a neat computer and with careful calculation and prediction of the best routes.
The technology has already been tested on a 25000ton ship (not "small" either), and it worked quite well, reducing fuel consumption by double digit amounts.
Anyway, you can read all about it at the website:
http://www.skysails.info/index.php?id=45&L=1
I see not many people have really looked into it carefully.
But the kite-concept is far more useful and many, many, many times cheaper than ordinary hypermodern rig concepts like this one:
http://www.platinum.matthey.com/media_r ... 88006.html
The above is a zero-emissions solar fuel-cell hydrogen sail ship - but it's just a hobby because it's ridiculously expensive. The skysail costs a fraction of it. It is also real.