What are the main disadvantages to a kiteboat in terms of long distance bluewater sailing?
A kiteboat is essentially a boat that uses a kite instead of a sail for propulsion. This seems like an intriguing concept, and an interesting alternative to the traditional sailboat designs. As advocates of the sport the website The Kiteboat Project has a big article on the advantages of a kiteboat.
The advantages of a kiteboat over a traditional sailboat are manifold. As a kite pulls a boat, it does not also heel the boat over or pitch it forward as a sail does. This fact means that a kiteboat does not require large counterbalancing forces which, in opposing the heeling and pitching forces of a sail, create drag and present practical problems. The absence of this behavior means that the only limit on kite size is kite control, since increasing the power made by the kite does not require increasing ballast or beam, for example, which are limiting factors on a sailboat. Kites can fly higher than sails, too, which grants them access to stronger, steadier, higher-altitude winds, and kites can be maneuvered through the air to create more apparent wind. This maneuvering generates extra power, which is not possible with a fixed sail on a mast.
Finally, a kite lifts the boat out of the water as it propels it forward, which effectively reduces the displacement and decreases drag. While any boat would benefit from this boost, a hydrofoil benefits especially, because the kite reduces the amount of lift required from (and drag created by) the foils, and the lack of heeling and pitching forces makes reliably maintaining trim and ride height much more practicable. It is not necessary for a kiteboat to be a hydrofoil boat, but for us, this configuration represents a perfect marriage of technology.
Of course this is rather new technology and it would be hard to find support in the form of replacement parts on in an isolated island port. Apart from the maintenance burden that would impose what are the primary drawbacks to adopting this style of boat for long-term bluewater cruising?
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The examples on the site only show inshore sports sailing with a hydrofoil. This does look like fun, and downwind performance can be exceptional. Though I doubt that inshore fleet racing would be possible as the kites would surely get tangled.
As for bluewater sailing, it seems that no-one is arguing that it is practical with current technology.
Masts hold sails up in light air, but a kite is going to fall at times. Even with adequate wind speed they need careful nursing to prevent stalling. Fallen rigs are hard to handle and relaunch can be impossible in difficult conditions. Do you fancy having the kite and rigging under your hull in the Southern Ocean? Or tangled under another boat in congested waters?
With current designs the minimum practical wind-speed is around 10k per hour. At present lighter-than-air kites that would stay aloft in light winds (using helium, for example) aren't seen as workable.
In tight situations such as busy ports or estuaries the kite would also be impractical and probably dangerous. In the demo films they are sometimes flying over other people's masts which seems pretty questionable. And they only just made it under the Golden Gate, so most bridges would be too low.
Another major issue is upwind performance. Current kite designs have a lift-to-drag ratio of around half that of a conventional rig, meaning that they can make less than half the speed upwind. Tacking is tricky, so you are generally restricted to gybing.
You are also restricted to sailing light hulls, as the largest workable kites are still quite small.
Finally, there's the question of handling gusts and squalls. With current kite designs control is cumbersome and there is a real possibility of structural failure, or of the hull being lifted out of the water with catastrophic results.
While there are potential technical solutions to these issues it seems that they are still some way off.
So at first sight this looks like a cool idea with a somewhat limited range of application - at least for the time being.
References:
http://www.peterlynnhimself.com/Kites_For_Yachts.php#top http://www.dcss.org/speedsl/Whykites.html
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I think the distinction of tack vs. gybe is a little hinky when referring to a kite boat moving into the wind since the kite would pass over the boat... something that a sail on a mast will never do. I see no reason why a kiteboat couldn't turn into the wind while the kite passed directly overhead. As for closest approach to the wind with a kiteboat, I have no good idea, but am really curious.
I see a couple big obstacles with kiteboats on the blue water: - Dealing with variable wind conditions. Multiple sized kites? How to bring down a kite that is too big when the wind gets strong? - Putting up a kite on a 100M line when lightning storms are in the area. Having a mast in the air is a little scary when the lightning strikes, but trying to duplicate Ben Franklin seems pretty risky.
Don't get me wrong. I think this is a really cool technology, and I would love to scooting around the world pulled by a big kite, but I think that dream is a few years off.
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There are many disadvantages. The most important of which disqualifies this technology from any serious Blue Water sailing ... you can't tack. because of that you are at the mercy of the wind and that is a cruel teacher. The artificial center of gravity issues are for people that want to minimize heeling which a catamaran or trimaran accomplish.
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