A good objective summary from my perspective Yoyo. As you say the, thoughts of the dozen or so in the 50 knot race should carry most weight. But spectators are part of a sport and we like the rules to be sound.

I think the WSSRC took the advice of the experts. In this case the Wolfson Institute who it appears did a search of the naca langley tank test US navy files (no need to reinvent the wheel).

This is quite an extentive data base of "real world" experimental data which I have used myself on many occassions.

I have not looked extensively for ground effect in water but have not found anything yet. I do remember reading years ago about differing effects on torpedos depending on the shallowness of the water and that ferry thing rings a bell as well.

If I do find something I will post the link here.

sailquik said...

The basic premise is incorrect.

The basic premise is well founded. The WSSRC are sticking to the definition of sailing. This as Ian pointed out before involves the interaction between two fluids. Using a solid boundary to gain lift is not in the spirit of sailing. Its as simple as that. The WSSRC appear to have acted hastily to prevent this being exploited in the near future by the sudden advancement of the kites, which clearly are running in the "grey area" in regards to this. Its important for the WSSRC to avoid such a fundamental precedent being established. If the ground effect is forbidden by the definition of sailing, and there are no rules to prevent it being exploited there is no problem, until the boundary is being pushed. Then new rules are made to protect the value of the record. They might not be perfect, but they address the immediate threats to the integrity of the record.

As for questions of it being exploited in the past- I can think of no configuration that has been a contender for the record where this is the case. As mentioned earlier, the vertical lift component on a windsurfing rig is mostly produced by aerodynamics, and since windsurfing foils run at low angles of attack at high speed, there is very little downwash, so there is little to be gained from the ground. A kiteboard on the other hand is running at significant angles, and can gain a significant lift from the ground in shallow water.

sailquik said...

If there is (and I think there probably is) and advantage to be had by sailing in shallow water this is no different to many other ways speedsailors have found advantages in the past. As long as the craft is physically touching only water and using some sort of foil in the water to counter the pull of the sail it is sailing. The example the WSSRC quotes of a craft with no fin sliding like a 'skiffle' board is clearly not possible. To sail faster than the wind, or even as fast as the wind one needs to travel at some angle across the direction of the wind and this requires some sort of sideways resistance and therefore some depth of water to lever against. Actually touching to bottom is the last thing that one wants as it will just slow one down. In this regard water depth is self limiting.

Where do you draw the line at acceptible depth? You cant say that its impossible to make a vessel that can "sail" on very shallow water because it needs something to provide lateral resistance. It doesnt make it impossible because YOU cant think of a suitable configuration. I can think of a few... At some point the ice sailing comes in. The lateral resistance is provided by shallow water being pushed against the ice. Why is that different to pushing off the edge of a perfectly formed speed course in 2 inches of water? How shallow is too shallow? Is it OK that I run in 1mm of water with a skate if I can prove that there is always water between the skate and the bottom?

This is not about banning kites, or some conspiracy against windsurfers and kites, as some have been claiming on various forums. Its simply about protecting the value of the records, which goes way beyond loyalty to a particular form of the sport. There is nothing stopping kites or windsurfers from running in 50cm of water. But in less than that the ground effect grey area kicks in... I'm sure the rule will be ammended at some stage to be a little less blunt.

The rule is about preventing the use of pushing off a boundary through a thin layer of water to gain extra lift. Its nothing to do with water surface state (waves etc).

The canal wall is not really a wall. Its quite uneven, and since it is located on the windward side, so is exposed to the low pressure side of the fin. Not something that would give an increase in lift or decrease in drag.

"Using a solid boundary to gain lift is not in the spirit of sailing"
Slowboat, can I get a refund on my solid boundry to gain lift device. Bought new from KA at Easter and still unused due to lack of suitable conditions. 23cm symetrical lift device in question is going to make sailing without very difficult so I probably will hang onto it.

There is nothing new in this old study. The question is, how the hell can they make money if the WSSRC comes to these conclusions. Or - probably the WSSRC has taken the wrong conclusions ?

Here are the relevant statements the WSSRC uses:
1. the ground effect becomes notable, when the beam of the board is wider than the water depth. This is WRONG. the effect becomes notabel when the beam of the board is wider than the DISTANCE to the ground. Otherwise, a hydrofoil can legally sail in 51 dm og water with its foils 5 cm above the ground.
2. taking this into account, the only fair solution is to make the rule dependant on the average width of the planing surface. Lets say 30cm for windsurfers ? 10 cm for kitebaorders ? So what about a 3m wide boat that sails in 51 cm of water ? In full ground effect, but - allowed !
3. Is this fair. This can be discussed. The rule as it is now is definately unfair. There might be the need for a ground effect rule, but not in this way.
4. Is this sailing. Definately yes. Is the vessel changing somehow when coming into shallow water ? Now, still the same sailing vessel. I am not talking about skimboards here, you all know that. I am talking about a vessel that CAN sail in deep water and takes advantage of a natural effect. Luderitz is probably 10-15 cm throughout the run, probably more, so definately not skimming.

Check the image landyacht has put in this post of then sailing a skateboard type device.

www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=38787

Then imagine a skim board and spinnaker in 60kts, straight downwind at 50kts no problem, (well as long as you don't crash!!!)

yoyo said...

Magic photos as he said "...water was only a few mm deep and the which is why there are no ripples. . Anybody thinking skim board and kite?"





Andrew when you say "For me it is very clear. A craft is 'sailing' if it supported on water and using some sort of foil or surface.." I agree, but Slowie and I know that in "ground effect" the craft is not supported by only water but ground and water. The closer to the ground the greater the proportion of lift provided by the ground. The WSSRC acted quickly to make sure that they weren't left trying to close the door after the horse had already bolted.

They realise that they will need to refine the rule, no doubt aware that MI on a 50cm deep salt pond will be in ground effect AND legal. However, as the challengers need to register in advance with the WSSRC their current rule dealt with the immediate ambiguity only.

Looking at those photos maybe I'll make a drive to Kal in the next winter storm with my gps, a sled and a kite. :-))

Still only touching water. Ground 'effect' is still water.
Good luck getting your foil to work in that salt lake. You won't be 'sailing'. You will be drifting dead downwind and that is dead slow. Lots of talk about going dead downwind on 60 knots of wind but I don't see anyone trying it. All the water on that lake would be piled up on the leeward side anyhow.
Ground effect is good! Just like hydorfoils, planing hulls, canals, etc. It has always been allowed in the past but I don't think it has had any effect on records and if you can find a way to take advantage of it in the future, good luck to you.

Not if you figure-8 the kite. Then the apparant wind could be quite a bit higher.

Actually , playing around on those apparant wind calculators you find even in windsurfing if if you go very deep even in a gale the AP drops way down. Which explains the light feel of the rig. I used to think it was the equalisation of the drag on the sail with the lift.

Not sure you're right there Andrew. There's the riders inertia he can play with, depends how much the kite has to be figure eighted.
It's not going to be as much as if the rider did have something to push on, but I'm sure he can manage something.

Ian K said...

decrepit said...

Not sure you're right there Andrew. There's the riders inertia he can play with, depends how much the kite has to be figure eighted.
It's not going to be as much as if the rider did have something to push on, but I'm sure he can manage something.

That's an interesting idea Decrepit. With no lateral resistance in the water the kiter would have to throw his weight to port as the kite went starboard and use the kite to save the fall, reverse the throw and continue the cycle. Shorter lines might be needed. But still only 10 knots of apparent wind to play with going for the record in 65 knots.

But kites are pretty effective in 10 knots when you swoop across the power zone - the kites apparent wind is much more. I was recently mucking about on the beach with a 1.5 m practice kite. Didn't have windsurfing gear but I would have rigged a 7.0. That 1.5 would lift you onto your toes as you swept across dead downwind. No wonder kiters with 12m up get dragged if they don't watch it.

Even if you could get the physics to work so that you could get the kite to "zig zag" downwind it is only going to be the net downwind force/velocity that the rider is going to be able to "use" as his speed ie it is the straight line distance of 500 metres that count. Curved course has been covered in debate extensivly elsewhere. As Andrew says without lateral resistance you cant go other than as the wind blows. Depth is a self limiting factor in sailing.

Ian, think you've missed the point, the rider/skim board wouldn't be doing any zig-zagging, just the kite.

I've tried a mate's kite when he was learning, in 5kts it was very hard to get in the air, wouldn't stay in the sky parked in the neutral zone, but swooped thru the power zone I was doing 20m heel drags. In 6kts, it would just hang in the neutral zone, could hold it with my little finger, but swooping thru the power zone lifted me head high.
I wasn't game to try swooping it in 10kts.

nebbian said...

I've watched a grommet on a skim board with a trainer kite going dead downwind in a couple of cm of water. He was in full control, no issues there at all, he even had some directional control. This was at Shearwater on the gold coast.

Granted he wasn't doing windspeed, but it's possible.

To get a kite to pull you along all you need is some form of resistance, it doesn't have to be lateral with regard to the kite line. All you need is plain old friction drag.

Hmmm.... I might have to get out the old skimboard and experiment. On the other hand, I might get my teenage son to do the riding. My bones aren't a flexible as they used to be.

Well it has been an interesting theoretical exercise, but it's getting a tad too complicated now!