kite for powerboat?

What is commonly wished for is a "skyhook" kite; one which sits where you want it and just pulls. Unless with full automation--far, far too expensive for yachting or small boat use, it does not exist. Kites (and other sails and flying things) have an inverse relation between stability and efficiency. A simple round parachute is very stable, but has a L/D of less than 1. A PL pilot kite has an L/D nearer 1.5, and even it occasionally (once/hour or so) falls in the water. In the meantime, neither kite can pull at anywhere but dead downwind--even a few tens of degrees off dead downwind results in an apparent wind with which such kites cannot cope.

A high performance kite can have an L/D as high as 6, even 8, but will be extremely unstable, requiring careful constant control. We don't notice this intereplay in boats, because we are used to it--we trim our sails almost constantly, if not with sheets, then with the tiller--we use the boat's course to trim the sails. This is also true for any kite efficient enough to sail on useful courses. OutLeader kites are quite specialized--and are one of the most natively stable kites available. They are not "skyhooks" however, and require regular tending, with tiller if not with sheets. This tending is different than what most of us are accustomed to with sails, so seems onerous. It is not.

Another poster questioned the usefulness of kites over sails for boats. The Big Deal is twofold; the kite does not heel the boat--meaning you don't need ballast and become more stable as wind increaseas, not less so. The second is cost--you needlt pay for mast, stays, reingorcing, booms, bulkneads, pullies, hard poinits for stays to attach to, etc, etc. You only need the kite; and can even transfer it from boat to boat as you please. Try this with a normal sailing rig!

Dave

 

thanks for the clarification Dave. I surrender...can't be done.....

 

Maybe what you need is actually a low L/D ratio kite as you wanted to have a type of kite or sail to use with the wind essentially behind you. Even conventional sails work mainly as drag instruments on a downwind run. This might allow a more stable type of kite shape which which would still require trimming and supervision, but probably less so, than the types used by kite-boards.

 

pabble, I thought you were asking for a straight downwind kite. that is why I mentioned the pilot kite. parachute might do it too, maybe even better. With boards surely you can steer some degrees from dead downwind, Dave, even with a singleline like the pilot?

 

downwind would be fine for me because I only need to get within 500 miles of my target, then can use the fuel and engine to the degree necessary. I anticipate being alone or with one other person so couldn't manage tending a kite continuously. And I'm interested in seeing how useful a kite might be in emergencies.

 

With my high performance kite, I can probably sit as long as the wind is reasonably stable without touching it.
The problem is the "high performance" part: it sits almost straight above me. That wouldn't be very useful for being pulled anywhere (except up).
If I were to pull the rear lines, it would increase the angle of attack, increase the lift, increase the drag proportionally more, so that it would pull more, and lower down - but there would be a threshold, where it would suddenly stall and possibly fall to the water. If I added a tail in place of the control lines, with lots of plastic bags, it might be able to keep its low angle of attack, and not stall, while also decreasing the total L/D of the kite so that it flies lower.
So I think frosh is right in that the easiest is low efficiency kite, with lots of drag on its tail, but I don't believe it would have to be trimmed after it is set. But you would have to be pretty consistently going slower downwind than the wind. I wonder if a long, stretchy line would help the kite stay up if you were to surf faster than the wind occasionally. The "lift" would only be needed to hold the kite up - the "drag" would drag you forward.

http://www.dcss.org/speedsl/ST89refs.html

"Dan Eisaman. Dan sails an 8 ft inflatable raft pulled by a 60 ft2 parafoil kite. Dan has crossed 4 of 5 Great Lakes and plans to cross Lake Superior in the summer of '89. He wants to tackle the Atlantic next: 26521 Barrington Rd., Madison Heights, Michigan, USA 48071."

"Ed Gillet. Veteran kayaker and sailor; completed a solo crossing of the Pacific Ocean, Monterey, California to Kauaii, Hawaii, in the Summer of 1987. He paddled/kitesailed a stock Tofino double kayak with a single line Jalbert J-15 parafoil kite. His trip took 64 days: 1310 Rosecrans, San Diego, California, 92106."

http://www.amoka.com/kayak.html
http://www.sit-on-topkayaking.com/Articles/SurfSail/KiteSailing.html
http://alpha2.bmc.uu.se/mark/kayak/kayak_kite.html
http://www.windpowersports.com/kites/single/kayak-kites.html
http://www.dcss.org/speedsl/KI1288.html
"I had a two-legged bridle on the bow and I noticed the boat yawing quite a bit. It wasn't supposed to do that. I fiddled with the bridles for the next hour or so, putting them first in one place, then another. I finally put them on either side a little aft and the boat swapped ends and stopped its yawing. I was crossing Lake Ontario backwards! The skeg was put too far forward. That's what I get for not trying it out first. Well, it didn't make much difference to me which way I went, forwards or backwards, as long as I was going steadily along at about 2 kts; or maybe 3 in a gust."
(Dan Eisaman)

 

It should also be possible to set up a keel/rudder system that will yaw a bit towards the wind when the wind dies or you start to overtake the kite on the face of a wave. this should make it harder for the kite to drop in the water.