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Speedboard Design PDF Print E-mail
Written by Basil Cambanis   
Sunday, 25 July 2010 05:24

This content was sparked by Christoff Muller, to which I've added my thoughts and ideas. 


The speedboard and kite designs seem to have stagnated over the past couple of years, and this means the chance of big advances in speed are unlikely unless some out the box thinking gets put into action.

Here are some ideas to get more out of the current boards (new approaches discussed below) :
 

  • The biggest hand brake on speed is friction, so to counteract this we should try to emulate Shark Skin, as is has proven low drag properties. It's so effective that swimsuits of this material have been banned at the Olympics.  There is a new product on the market which does just this, and we should use it on the bottom deck to aid water release.
  • Speed kiters need to counteract tremendous lateral forces from the kite, and they do this mainly by edging hard; but this results in more drag and counters the path of least resistance. That's why kiters are fastest at a broad angle off the wind; but this also means more chop and swell, and less use of apparent wind. So adding a few small steps in the hull will encourage early water-release and provide better lateral resistance. They'll also result in less wetted area when at high speed as the water will spray off a step and have less surface contact with the board.
  • Adding a small progressive lip on the heelside rail will also counteract the lateral forces, and aid in better tracking and quicker stopping time (which is always and issue).
  • Hard rails by tail progressing to beveled rails towards the nose will also aid in water release. But this needs to be weighed up against the water state. However, a softer rail will give you better control (more speed) in choppy conditions.
  • I prefer a longer board (155+ cm) as I'm tall (6'2") and find that a longer board is less prone to bitting into chop (less drag). It's not pleasant when going broad over swell, but that's not the domain for speed anyway.
  • Rocker plays a vital role, and I believe it should be fairly flat by the tail and progress to more rocker towards the nose. But rocker should never be excessive, and it must be continuous. I'm in 2 minds about having micro steps laterally, but it'll require some testing.
  • Flex plays a vital role, and should progress from moderate to little or none by the nose. This allows the board to soak up chop, store energy and release it when appropriate. It gives the rider far greater control which results in fast speeds.
  • We could speak about cloth Layups for a while. Carbon is usually the most desirable as it's stiff and light, BUT it might not be the best materialin this case as it results in a board that's too stiff and eventually fails due to the rigors the chop subjects the board to at high speed.
  • This is one of the few occasions where adding Weight in the right places can help. Kiters are going over 100 km per hour which equates to a lot of wind force; this coupled with the chop means the board is prone to literally flying out the water. Carefully placed lead weight on the board will counteract this and allow the board to drive through chop/swell better (more momentum). Weight should be placed midway forward, never by the tail. This can be done crudely by bolting weight on, but this presents a danger when you wipe out; or it can be done internally using channels beneath the deck.
  • Due to the high loads placed on the footstraps, I recommend the inserts be made as bullet-proof as possible, as if they fail it'll ruin the board. I've had a strap pull out at 90+ km per hour before, and besides the obvious hard wipe out that ensued, I almost had my other foot twisted off in the process.

 Speed auxiliaries I recommend :

  • Back protection is a must if you plan on pushing the limits. I know of 3 kites who have broken their back during wipe outs. The pro's recommend Dainese who specialise in snowboard safety equipment. Think of it as an insurance policy you hope you'll never need.
  • Having an accurate waterproof GPS is a must. It needs to be highly visible so you know how you're faring in your approach, during and after your run. I use the GT-31 in an Aquapac. I'm trying to organise a waterproof housing for better display.
  • Normal twintip fins will work, but it's advisable to try and source dedicated speed fins. This is easier said than done. Microfin in France seem to be the leader in this regard, but I haven't got a web address or contact details for them yet.
  • A kite repair kit is a must, as the fabled speed spots tend to be far from civilisation (e.g. Luderitz), and one hard wipe out can result in breakages. It should have various sizes of bladder patches, glue, valve stoppers, scissors, spare kite line, thread and needle and some dacron.
  • I have not worn these in the past, but I'm strongly considering wearing shin guards, as I whacked them many times and nearly broken a shin on one occasion when I slammed into the rail of my board during a wipe. 

 

 Crystal Ball gazing :

  • I believe that hydrofoils hold the key to us to reaching 60+ knots on a regular basis; the high-speed control issues will be resolved (Hydroptere solved it). They'll allow us to kite squarer to the wind which means better use of apparent wind, and they'll take chop out of the equation.
  • We need a wing-type design of kite to get better efficiency in less wind. We also need to perform better in squarish wind. A double layer canopy might be the answer. It's been prototyped in the past but never made it into production, due to high cost of manufacture, water filling the void and other issues.
  • We should heed of the lessons learnt by the windsurfers and try using a windsurfing type speed fin, just much smaller (8-10cm ?).This will give us great efficiency squarer to the wind, which I believe is the key to us reaching faster sustained speeds.

 

Martin's fin
Speed fin of Martin van Meurs who is the fastest Dutch sailor

 
Speed sailing is mostly waiting, training and timing; and then a brief burst of action. 
But those few seconds of pure magic are imprinted in your brain for life.

 

 

Here's the mail from Christoff Muller that sparked the debate : 


I've been thinking of speed board designs, and have a number of ideas that I think are worth considering :

 

1) Hydrofoils - have you seen the twintip hydrofoil ?

http://www.synapsekitesurfing.co.uk/products_hf.htm 
The guys say its get out of control at high speeds : http://www.kiteforum.com/viewtopic.php?t=2361561&p=659401.
I don't think any hydrofoil will work in the near future. At +50knots the thickness of the hydrofoil will have to be so thin that I can't imagine it being controllable.

 

2) Board surface friction.

2a) creating straiter rail edges. The curve at the trailing edge just before one' rear foot looks a bit suspect to me. I don't know whether the curve actually causes more drag since its off the water mostly, but I would guess that straight edges at the back might be more streamline. One way that we could implement a narrower more streamline water contact surface under the rear foot is to use the principle showed here : http://www.surfresearch.com.au/00000190.html.
The rear foot's toes would effectively hang in the air when the board planes nicely.

2b) Surface texture. Smooth and flat always seems smooth, but at the high speed we do over the water, I think a textured surface would be better. And we don't have to design the texture pattern ourselfs. We can just look at fish skin. Scales. Apparently, the high tech swimsuites developed by speedo mimic shark skin texture, an they claim an almost 8% drag reduction! http://www.swimming-faster.com/ And it can't be all marketing gimmick, since full body suites are now banned by international swimming.

I am very interested to see what difference such a texture would make to the kite board.

 

3) Fins. We are still using very low aspect ratio fins. Have you ever considered high aspect ratio ones? Instead of being 5cm deep and 10cm long, we should try 8cm deep and 3cm long. I also think we can redefine the speed we reach on a square reach by riding on the fins instead of the edge. Maybe we should try 2x 10cm deep fins, one at the back of the board and one between the feet and then ride the board much flatter on the water so that we use the fins instead if the board edge. Obviously the fins should be very thin and very narrow to lower its drag. This will mean we need slightly deeper water, but not too much.

 

4) Kites. If we really want to improve speed in a safe way, we obviously need a more square reach. Hopefully the riding on fins instead of the edge idea works, which mean we need a kite that has lower drag so that we can go faster on a square reach. I think we are reaching a maximum speed that inflatables can go due to their high drag. I doubt inflatables can go much faster than 40 knots on a square reach, even if board drag becomes zero. For example, in a 50knot run at 45 degrees downwind, the speed component perpendicular to the wind is only 35.4 knots. But, the speed component downwind is also 35.4knots! You thus need more than 35 knots of wind just to get any energy out of the kite at that speed!

Assuming the wind speed is 40 knots when you do a 50 knot speed run at 45 degrees, the speed that the kite cuts through the air only 35.7 knots. Thats why an inflatable seem to be able to go fast, but it does not really go that fast. I think we need to start going over to racing foil kites, and then do square reach runs (in much lighter wind as well). I see the fastest kite in the world is currently the Peter Lynn Vapor. They broke the previous buggy record this year, and their speed is now 72 knots!

http://www.surfertoday.com/kiteboarding/3268-arjen-van-der-tol-breaks-the-kite-buggy-world-speed-record-with-1334-kmh

 

The only problem with high performance foil kites is obviously lack of depower. The depowerable type of foils (Ozone frenzy and Flysurfer) is unlikely to be as fast as the racing kites (Ozone Yakuza and Peter Lynn Vapor). The racing kites have a much flatter profile and a much higher aspect ratio I think. Adjusting their profile does not give a flyable kite anymore. (I have a flexifoil Blade II 9m, and I tried adding a variable angle of attack for depower like on flysurfer kites, but did not get success. The airfoil is just too different. The racing kite are normally flown on handles , which I don't want to be doing at +50knots. I think the way to get around this is to do what flexifoil did with their blade III with the VPS system. It is basically similar to a bow kite in that you have a 4 line bar setup and pull the bar or out to power/depower. Only when you let the bar out, the angle of attack does not change but the kite profile distorts, thus depowering.

You cannot fly nicely depowered obviously, but at least you can depower to stop. When surfing you'll have to stay fully powered up.

http://www.flexifoil.com/webdownloads/instruction_manuals/Flexifoil_VPS_Inst2004.pdf

 

 

 

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