ISAF vs KITE Sailing

I see you modified your reply. Seeing as how I'm currently challenging the local establishment in my own way, I'm not quite a fit for what you originally wrote.

You've been making some pretty aggressive statements here. Your ideas might be earth shaking, maybe not. You haven't provided any real data yet, and you don't seem to like to answer questions head on. As Dr. Deming used to say, "There are no opinions, there is only data."

Let's see your tech in the crucible before we make any judgement.

 

im not going to straight out say that i dont believe in kites, because that would be unfair to those who sail with them and know more about them than i do. I think that off the wind, they are usefull, and the OUTLEADER kites are a good idea that shouldnt be banned by rating rules. However, I still question the idea of a boat being able to sail upwind faster with a kite than without. Does anyone know what would happen if you gave an IACC boat an upwind kite. This would all be theoretical, of course. Right now, those boats can achieve at least 13 knots hard on the wind, and some are rumored to have slightly faster than that. So say that you give an 85 footer a large upwind kite, will it be able to go at least 13 knots? Off the wind, an Outleader type kite should murder a conventional spinnaker, and that is what they are designed to do, as they are spinnaker replacement kites. Does anyone have an ideas on this?
thanks-
-usa2

 

My view would be that future kite designs may well achieve better windward performance than is possible with conventional sails but current kite designs will not achieve this. The lift to drag ratio of the rig (using the aerodynamisist's meaning for the term lift) is crucial to optimum windward performance and from a discussion with pioneer kite sailor Cory Rosseler a couple of years back I understand that the lift to drag ratio of typical kite sailing kites is in the region of 3:1, including line drag. This is a poor lift to drag ratio compared with that which can be achieved with wing masted rigs and solid wing sails. However I believe that the potential exists for much higher lift to drag ratio 'kites', which could for example have ridgid aerofoils and automatic (electronic) controls to allow flight control without multiple tethering lines. Such 'kites' may or may not prove to be practical for general purpose sailing but I think the potential must exist for speed sailing and record setting over both short and long distances.

If one were to optimise a kite powered craft for upwind performance I dont think an america's cup yacht would be a good starting point. One of the big advantages of kite rigs is that they do not necessarily impart any heeling moment on the craft they are attached to, and can indeed be arranged to stabilise a craft in heel. Hence a ballast keel is not needed on a kite craft, and would be just unecessary weight.

 

I have assumed that kite boards must be able to go upwind somewhat, at least a close reach. Am I wrong about this? Otherwise how do they get off the beach during an on-shore, and back to the beach with an off-shore?

So wouldn't those same type of kites be able to sail "upwind" on bigger boats? Anyone know how close winded you can get on a kite board (tacking angle)?

VMG is more to the point than discussing ultimate speed. ACC boats might go 13 knots upwind as stated by USA2, but it's the VMG that is more important. They tack in less than 70 degrees, so they are really putting that speed in the right direction.

 

How is the drag distributed thoughout the rig? I would expect the structural members to be lighter & thinner without any heeling moment, so that leaves the line?

 

Hi John,

It's been awhile. How are you doing? You make some excellent points.

Kites have improved a good deal; on short lines, the best regularly manage 5:1 to 6:1, including lines. This is on a par with a good soft sail rig, including the mast plus standing/running rigging, but not as good as a wingsail, of course.

There are far more weatherly kites than those currently used for kitesurfing, which are specialized for power, not efficiency. However, putting high efficiency kites on boats has a fundamental physics problem--an efficient kite can dive, across the wind window, at 3-4 times wind speed. In doing so, the energy they extract from the wind increases by a factor of 9-16 times(!) It is this wide max/min ratio which is hard to deal with. Fine for kitesurfers; not so fun for the family cruiser. Still, there are solutions, some of which are nearing the market.

Dave

 

so, like as Paul B said, IACCs tack through about 70 degrees. I think the apparent wind angle they sail to upwind is some ridiculously small number like 30 degrees...maybe a even a little less than that. And they do 13 knots. Could a well designed and built upwind kite be able to produce that kind of efficiency going to weather? I think the kites are obviously the answer for outright speed records, but typical racing sailors, whats the use of a kite if its illegal. Also, if say an upwind kite really did work, how does one tack the boat?

 

It's some of both, Skip. An inflated kite on the end of a string--which CANNOT weigh more than perhaps 5-10 pounds--cannot typically maintain as efficient a shape as a rigid wingsail weighing 20-40 times as much.

Plus the lines are pure drag--no lift. (Interestingly, I am just now in the California desert doing some research for the Army into kite line drag and how to reduce it practically. OK, they call 'em "parachutes" but we see kites. ;-)

It's physically (well, theoretically) possible to make kites better than the best boat wings, but it's not likely to come to pass, for cost and safety considerations (think hard-wing kites falling on your head), though guys have achieved 12-15:1 with experimental kites. These kites look suspiciously like large model sailplanes, tethered to the ground and flown as kites.

In the meantime, kites can out-pull any sail of the same size (increased wind at altitude; ability to "work" the kite, keeping it always moving faster than the boat), can lighten the boat by 50-70% by eliminating ballast, beam, strength in the ends of the boat (kites only attach amidships), and reserve buoyancy, which kite boats do not need. They also can pull non-sailboats, such as power vessels, ships, oil rigs and icebergs. Since they are self-supporting and self-deploying, they make dandy "get home" devices, for self-rescue and even for finishing races without the rig. We've got an article on our website about our trip from the Caribbean to the Upper Chesapeake last May with a dismasted racing tri.

BTW, I'm talking about kites in general, not about OutLeader kites, for the trolls listening in. ;-)

Dave

 

USA2; NOTHING can beat an IACC boat to windward, short of the best C-cats. They don't tack through 70, but more like 50 degrees. They sail within 15-18 degrees of apparent wind. (You may know that we developed the OutLeader kite for BMW Oracle Racing, for the 2003 America's Cup. Not an upwind kite, but we spent a good bit of time aboard these boats. They are AMAZING boats.) In anything under about 10-11 kts, an IACC boat can make good either dead to windward OR dead to leeward (VMG), better than the true wind speed. Nothing short of C-cats (and maybe A's), land sailers and iceboats can equal this.

Kites aren't going to beat $100 million world-class raceboats. They CAN beat whatever you sail, though. ;-)

Kites are not illegal in sailboat racing, with a very few exceptions. The issue (the reason for this thread) is the ISAF's not recognizing outright speed records under kites--they have ALWAYS recognized kite boat speeds.

Kites do not tack, they wear. It will be many years before a pure kite boat can beat even good boats around the cans--which is why my company is focusing on downwind courses anly at present, where kites have their greatest advantage. (Yeah, including downwind courses around the cans)

Dave

 

Not Quite.

Watching the last couple of LVCs and ACs you could track all the boats tacking through about about 65 degrees. At a TWA of 32, TWS 15, Speed 12, you have an AWA of about 18.

If you try a TWA of 25 (tacking through 50) at the same wind and boatspeed you get an AWA <14. Maybe they can punch up to that for short periods, but they don't sustain that.

 

There, see, you CAN post without trolling. I'll concede your numbers, they sound good; though have been aboard AC's short-tacking through +/- 50 degrees. Pro'lly short-time stuff, as you suggest.

Dave

 

AC boats cant sail 13 knots while tacking through 50 degrees. They can sail that high, but in that case, the wind is lighter and the apparent wind is the same...Which i believe is about 25 degrees off the wind. In all the Cup races i have seen, the boats dont tend to point any higher than 25 degrees, or so i have noticed. As the wind picks up, they will start tacking wider angles, but the apparent wind remains the same. So in anything under 10 knots the boats will be tacking through about 50 degrees, but I was referring to when the boats are traveling at full speed upwind, which is 13 knots in about 20+ knots of wind. The only time they will start pointing that high while the wind is strong enough to have them going 13 knots is if they are low on a layline and need to get above the mark. If the wind is moderate, then on average they will tack through about 65 degrees.

 

Many decades ago someone asked the AYRS (Amateur Yacht Research Society) in England what would be the most "efficent" sail boat.

The response was a submerged boat towed by a kite,

Looks like were half way there!

FAST FRED

 

I think you must be mixing apples and oranges at times, regarding TWA and AWA. The boats do not sail within 25 degrees TWA in light air, then drop off 7 or more degrees to 32+ when "the wind picks up." They may sail as low as 25 degrees AWA in really light stuff, but that sounds too low unless they are accelerating out of a tack. Can you cite your reference for the numbers you're claiming?

In fact, in light air as the boatspeed approaches the TWS the AWA moves Forward. In light air monohull boats in displacement mode normally sail lower angles than they do as the wind fills. Not only are you working against the TWA/AWA shift, but in light air your sails are fuller.

Of course, if the chop increases with the TWS increase the boats may need to foot a bit to get to targets.

Also, if you are talking about a planing boat (NOT an ACC) it can be beneficial to foot to transition to planing.

 

I'm guessing you saw this in Scientific American magazine. Theo Schmidt has done a good bit of work on efficient boats; and first (to my knowledge) suggested submerging the hull (to abvoid surface waves) connected to a kite (to avoid all the drag issues associated with heeling). Of course, he didn't adress the issue of the flying lines--both above and below the water.

Dave