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 Post subject: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Thu Nov 29, 2012 7:48 pm 
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I think it is time for the speed kiters amongst us to get back to the drawing board and think about a new way of getting the speed record back. Obviously we need to think about efficiency. 65 knots is super fast!

I think we need to consider board efficiency first. I think this is our biggest obstacle, since edging is simply not efficient. But big fins are only efficient/useful at low speeds. Does anyone know what the top speeds are for guys on race boards with big fins? It must be around 35 knots before the fins cavitate or vibrate or pull in air or whatever it is called (i.e. simply become useless at going faster). So what can we use to create lift that counters the kite downwind force? Sail Rocket proves that a foil/fin/keel can be useful up to 65 knots, but we will need to come up with a new idea to beat that (if we still want to of course. 65 knots is fast and dangerous).

Maybe we could use more than one edge? I've read that speed kite skiers go much faster than speed kite snowboarders, because two edges are more efficient than one. (effectively lengthening the edge). But will that give significant more efficiency to go to 65knots. Unlikely. Control up to 40 knots on one edge is difficult enough.

I think we need to look at a new technique. Cars have sideways resistance, yet little forward resistance because it has wheels. Why not make water wheels? (sounds silly?) What I think we should do is make a fin/wheel that allows the foil to see 20 knots of water speed when we are in fact travelling 60 knots. Just like the bottom part of a tyre of a car sees 0 km/h when the car is going 120km/h. The man who's idea it is has a interesting book (but for a different application) at http://www.amazon.com/dp/B0053NYVMM with a chapter on what is called a wheel keel. In its simplest form you can think of the fin being a wheel, and the wheel rotates like the wheel of a car so that the water flowing over the foil of the fin travels over the foil slower than what the craft speed over the water actually is.

So could we apply this to a kiteboard? I think so. I think if we take a race board, and replace the fins with large air-foiled wheels (with most of the wheel above the board and only about the bottom 1/4 under water) and allow the wheels to turn than we might have a race board with unlimited top speed? The wheels could have small brakes, that allow you to set the tension, so that it allows the wheels to turn like a wheel, but not so fast that the foil part of the wheel goes at the same speed as the water. We do need some water flow over the foil/wheel to get lift to counter the kite, but we just don't want this flow to become too fast that the foil becomes useless.

Obviously a wheel will not allow us to have the best asymmetric high L/D foil under the water, but at low water speeds this should not be too much of a problem. With the wheel we can basically adjust the foil to see at optimum water speed, regardless of the speed we are travelling over the water.

Does it kind of make sense to anyone?


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Thu Nov 29, 2012 8:08 pm 
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Make a water wheels board like you describe that works and goes as fast as a normal board and I will buy you a beer.

Aside from using an unusual hydrofoil, Sailrocket's major design advantages include:
1.a solid wing for less drag and greater control
2. refined aerodynamic design -frontal area described as < 0.75m^2
3. elimination of heeling moment

The kiter himself is the greatest limit at this point!
The human body turned sideways is not as aerodynamic as a fuselage.
The control system requires dealing with heeling forces etc. using the body to control board and kite.
The lines are more of a problem the faster you go, and so on...
Once they get to v3 sailrocket, they may see 80+ knots.
It's very hard to get there!
But kiters can go faster than the current 55.65kts, and will...
How to improve design for this?
Everybody has ideas...
;)


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Thu Nov 29, 2012 8:56 pm 
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the kiteboards use an identical property in their boards as the sailrocket does.

Specifically a surface piercing foil. Exactly the same as a sailrocket does.

Where the sailrocket beats us is in their kite. If you look at their speed run, they look nothing so much as a proa or sailboat but more like a kite held low and edging like hell.

We need a kite without this big thing in the front. The tube thing.

This is all on Cabrinha. They are the masters of racing kites, and need to step it up. Maybe we have to go back to battens, I dunno. Gonna take a lot of R&D on the kite end.

We are ok on the board end.


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Thu Nov 29, 2012 9:11 pm 
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just build the sailrocket without sail in small and stand on it!


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Thu Nov 29, 2012 9:33 pm 
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i can see someone vacuum bagging a solid kite wing for this to get a predictable foil profile, and trying out new fin ideas with lift


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Thu Nov 29, 2012 9:48 pm 
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Good to see some thinking outside the box, I think the comment about the solid wing makes a lot of sense, I find that in strong gusty winds my LE distorts no matter which kites I've used or how much air I've forced in, there is a limit to how hard we can safely pump the LE without stressing the stitching. As speed riding only takes place in bigger winds would some extra material and weight on the LE really matter if it meant we could put more pressure in? or do we need an absolute speed specific kite as suggested with a form of batten, problem is who is going to put money into R&D into such a small part of the whole kite industry. Speed must have the smallest number of participants of all kite disciplines. I'm not sure much more can be changed with boards that will give more than a few knots extra but I think on one of Tillmans videos where he is riding what is essentially a lump of ply "no offence meant" it looks like it's a double decker? If so does he have something there? what if once a decent speed is reached the main board rises up to let a slimmer board take over with less resistance, only downside I see to this is stability at speed and more depth needed. Back to the kite, the fastest kites any of us will have ever seen are trick Delta kites so do we go way back to the original kites like used by Corey on his water skis?
On a side note this year I've been introduced to mono skiing and now have my own, just a few more tows behind my boat and I'm going to give it a go on a kite, I will either get hurt or discover something, who knows.


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Thu Nov 29, 2012 9:57 pm 
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Well realizing that one needs specialized gear is number one...

Remember the kitewing? Well it would seem that could be attached to lines and lifted up. I mean these speed runs are in relatively controlled areas, and it would certainly be an option to fix the wing better.
I would think the board could be a race type board, but with different fins. Maybe more shallow and longer to make it go in shallower water to minimize the chop affecting the board....

At some point there will be problems holding on to the power because of the increased drag in water and power needed to increase speed. This is not a linear function as far as I can see. Could we make a board with an outrigger?


http://www.dailymotion.com/video/x4jbc8_kitewing-kite-wing-2006_sport


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Thu Nov 29, 2012 11:02 pm 
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tautologies wrote:
At some point there will be problems holding on to the power because of the increased drag in water and power needed to increase speed. This is not a linear function as far as I can see. Could we make a board with an outrigger?


If the limit is how much power you can edge against, then going at a more downwind angle in higher windspeeds might be the way to go.

ChristoffM wrote:
Does anyone know what the top speeds are for guys on race boards with big fins?


I remember reading that on one of the lighter days of the recent North American Speed Sailing Championships, they were riding race boards down the course and getting very high speeds. Did they break 40 on the race boards?


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Thu Nov 29, 2012 11:30 pm 
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To come up with a better design than Sailrocket?
It was designed from a blank sheet of paper with a high budget and very very few design restrictions. Its only purpose is to be the fastest wind powered thing on the water.

It has a fusilage which points not in the direction of travel, but directly into the apparent wind. That is the equivalent of a streamlined kiter on an outrigger, lying horizontally on his side.

The board might work better with a bottom curve that turns down into a vertical edge. This has already been done on speed kiteboards and obviously didn't work well enough, but it might still be worth looking at as it may become more relevant for higher speeds.

When racing downwind in light winds, they go faster by looping the kite - that again may be something that would be relevant if going deep enough downwind.

The windsurf sails are pretty efficient now. In strong wind, the weight of the kite is less important. It may be that you could take two Neil Pryde Evo V windsurf sails and join the masts together at the base to get a relatively cheap solid enough wing.


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Fri Nov 30, 2012 2:44 am 
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Maybe I’m missing something here…. but I can’t see how the SailRocket can sail on the other tack. (Please correct me if I’m wrong on that. If I am wrong, then most of what follows is, too.) Its success has been built on optimising it for one tack only. Which is losing the plot in my opinion.

It got them the record, which is what they were chasing, so good on them. They achieved their goal.

Prioritising one aspect of performance (ie speed) is always going to necessitate compromises on other aspects. Just as there are kites and boards to suit different styles of riding. But compromising to the point where only one direction is possible??? It’s a step too far for me.

Kiters may be forced into similar undesirable compromises if they really want the record back.

My design concepts would include:
1. Attaching the centre lines to the board rather than the rider to virtually eliminate heeling;
2. Using a shroud for the rider to reduce drag.

In other words... use a boat, not a board.

But then the real compromises…
3. Use an outrigger. (This wouldn't necessarily be as bad as the SailRocket’s compromise, because the power could be transferred through the main hull, so it could still sail on both tacks – just better on one than the other.)
4. The kite could be optimised for a single tack with the foil and angle of attack varying with the height above the water. (Obviously need some serious engineering to get that right, but I think it could help.)

In the end, I think the result would be something that is so far removed from the sport that we know and love as to no longer be worthwhile.

When windsurfers and, later, kitesurfers held the record, their equipment was specialised, but still very recognizable to the weekend warrior. The technology played a part, (probably even feeding back into the development of recreational equipment) but the main difference between the record holders and the rest of us was the skill level. And so the record had aspirational value. I think the SailRocket changed that.


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