Slowie said.."Again, the issue is whether using the ground for advantage is in the spirit of speedsailing. We might only be talking about a few % in drag, but thats enough to smash records."

It is alot more than a few %.

If you look at the graph below, which is real experimental data, you can see that when ground effect comes into force it doubles (from 6 to 12) the lift to drag ratio and when you put end plates on ( ie kite board with fins) you triple (6 to 18) the lift to drag ratio.




Tilmann says he sails in 2cm. He is getting lift from the ground . That is not sailing on water.

yoyo said...

Slowie said.."Again, the issue is whether using the ground for advantage is in the spirit of speedsailing. We might only be talking about a few % in drag, but thats enough to smash records."

It is alot more than a few %.

If you look at the graph below, which is real experimental data, you can see that when ground effect comes into force it doubles (from 6 to 12) the lift to drag ratio and when you put end plates on ( ie kite board with fins) you triple (6 to 18) the lift to drag ratio.




Tilmann says he sails in 2cm. He is getting lift from the ground . That is not sailing on water.

YoYo and Slowie. I think that perhaps you have opened up a debate in which everybody is entitled to express an Opinion as to whether a craft utilizing the ground effect is sailing on a body of water. My personal opinion is that it is sailing on a body of water when the draught of the craft is greater than the water depth (ie not sliding on a water lubricated low friction surface). The graph that you show YoYo appears to me to show a significant increase in lift from approx 0.25 h/d but the lift continues to change at a lesser rate till the end of the graph h/d equals 2. This brings up the issue of where will you draw the line of what constitutes ground effect as from this graph a windsurfer in 50cm of water at SP will have a ground effect (admitedly so small as to be insignificant but ground effect assisted nonetheless).

snides8 said...

last time i checked water didnt compress all that well, could some 1 explain in laymans terms how the ground effect with water in between works?

One plumbing layman to another,so lets take compression out of the picture.
This leaves us with friction of water against water increasing as it is forced out of the way, potentially applying more force to the object pushing it out of the way as the space the water is contained in decreases in size.
To me this means any body of water with a hard bottom holding it up has ground affect - some people are trying to set a limit on how much ground affect is allowable to suit their own needs.

A very interesting discussion, with obvious ramifications for all.

Snides - when you apply a force to an object, that object applies an equal and opposite force to you. As you mentioned water cannot be compressed. So in very shallow water, the water it is effectively sandwiched between the bottom of the board and the ground, and applies an equal amount of force to the bottom of the board that the board is applying to the water. So the water can act not so much to lift the board, but prevent it from sinking. Think - skim board. Great in very shallow - glides great, try them in waist deep and they sink very quickly. Mainly because the water molecules are not confined so much and are able to move allowing the board and rider to sink / displace their volume of water.

As far as I understand the arguments - this rule does not directly affect GPS sailors at this time, furthemore, I thought the depth of water is of less consequence to a windsurfer than the amount of chop on the surface. I realise that it seems that a number of good potential record sites will be affected by this rule - but that will only be for world records. Will it affect the speed world cup? If so then this would have to be addressed.

Final note - are kites sailing? In no way am I starting an us and them argument. But as mentioned earlier ice sailing is not sailing, so is kite surfing sailing. There are many categories for motorised speed records ie motor cycle, standing-start, flyingstart etc and then you have the overall land speed record which is usually a jet car of some sort. Same with powerboats, so why is there no push to differentiate an open world wind powered record for the different mediums land, ice, water etc. And leave sailing as sailing. I'm sure that kiters would set the guiness record for the fastest wind powered craft over water, but if it is not sailing then why should the WSSRC be involved.

If anyone could clarify the kite surfing is indeed sailing then please let me know.

What defines sailing?

Nice chat

Andrew, I think you are missing the point with this lateral resistance stuff. Sailing craft have been sailing dead down wind for thousands of years. Lateral resistance against water doesn't define sailing. I would have thought craft supported by water (whether hydrofoil, planning or displacement) powered by wind would be enough.
The physics is clear. Kiting in shallow water exerts force on the ground which exerts an equal and opposite force on the board via the incompressible liquid,water.
So whilst the kiter is on water a large part of the supporting lift is provided by the ground.

Yes, the graph was from an air ground effect study. But this makes it even more compelling. Air is compressible water is not. From that one should expect that ground effect in water would be even more noticable. The figures the WSSRC give from the Wolfson study indicate that this indeed is the case.

I note a post on gps-ss mentions that it would be easy for MI to sail in ground effect legally with this new rule. Maybe a rethink/rewording is required.

yoyo said...

Andrew, I think you are missing the point with this lateral resistance stuff. Sailing craft have been sailing dead down wind for thousands of years. Lateral resistance against water doesn't define sailing. I would have thought craft supported by water (whether hydrofoil, planning or displacement) powered by wind would be enough.
The physics is clear. Kiting in shallow water exerts force on the ground which exerts an equal and opposite force on the board via the incompressible liquid,water.
So whilst the kiter is on water a large part of the supporting lift is provided by the ground.

Yes, the graph was from an air ground effect study. But this makes it even more compelling. Air is compressible water is not. From that one should expect that ground effect in water would be even more noticable. The figures the WSSRC give from the Wolfson study indicate that this indeed is the case.

I note a post on gps-ss mentions that it would be easy for MI to sail in ground effect legally with this new rule. Maybe a rethink/rewording is required.

Yo Yo I don't quite get your point. I am sure that we could all come to some agreeable definition of sailing. Lets say getting from point A to point B and back on an open body of water using wind power alone. Then define a sailing craft as one which is capable of sailing. Kitesurfers and windsurfers fit the definition and anyone can go out one afternoon to qualify their craft for future speed record attempts.
Then ban ice from the course (as it is already) then ban the use of a water lubricated low friction surface material course.
Then if you want to sail in a 5cm deep course using your fin to plow a path through the mud no problem. The onus of proof will lie with the kitesurfer to prove that he is not sliding on a water lubricated low friction surface. Shouldn't be too difficult on a sand/mud flat. The ground effect in my opinion does not take away from sailing.

Ian K said...

decrepit said...

The common equation for all deep water non-displacement craft - whether planing hull, fully or semi- submerged foils, supercavitating foils etc is

Mg = d/dt(mv)

What does d/dt(mv) mean?

<ed> Never mind I looked it up. It appears to be delta time x momentum which is the same as ma. So Mg = d/dt(mv) is another permutation of good old F = ma. (I think)

This topic is not as complicated as it appears... there is only one aspect of this that needs to be considered, ie: at what point does a body of water become "lubricating"? And I guess that I may be stating the obvious... the lubricating effect will depend on depth (assuming the liquid is constrained) and viscosity.

The change lift, drag, etc due to ground effect, is interesting and it is quite ingenious to use the ground as a end-plate for the fin/board (eg: formula fin in 80cm water, would probably still classify as sailing), but what we should focus ** on is the depth that is required so that the water beneath the vessel, becomes constrained -> so that it exhibits a very large (relative to speed) lubricating effect. Measuring lift is one possible technique for measuring this, ie: the lift drastically changes at/around some depth.

Note that I personally haven't formed an opinion on what depth should be a minimum, as I cant find any studies indicating when the lubricating effect starts to dominate (for an open body of water, such as a beach). I would however state that "sailing on land using a lubricant, isn't sailing on water".

And for those that say ice-sailing uses edging, think dead-downwind sailing, where for directional stability you could use some air-foils -> you would however probably be limited to a max-speed same as the wind.

** Some people may choose to require sailing vessels to be "well defined" (aka: pure) - I'd argue that that idea is self-limiting for no particular reason, eg: is kiting sailing?... but that is a discussion for another thread.

nebbian said...
[
Or is my logic flawed?

Firstly, tell me how fragile is your ego Nebbs?

hardie said...

nebbian said...
[
Or is my logic flawed?

Firstly, tell me how fragile is your ego Nebbs?

Hardie, Aren't you a shrink? If so isn't that an unethical question.

this was done to disqualify people being able to beat records for <$2000 and forcing them to spend millions building composite boats just for a speed... This is just a case of the rich having a bitch and getting their way. what is more impressive, skimming with a kite in water too shallow to save you in a crash of sitting in a multi million dollar tri or hydroplaning craft and going as fast. hydrofoils deliver the same sort of reduction in drag principle as shallow water with the difference being that the hydrofoil is a matter of design and the skim just how ballzy you are with ropes pulling you very hard.

elmo said...

I'm more concerned about the legalities of wearing a stylish Red fury outfit

[}:)]

choco said...

What about the effect of tides? when the tide is going out at Sandy Point there must be a 1-2 knot speed advantage.
I remember sailing at a speed comp there in the early 90's and our timed speed runs over 250m were adjusted to take the tide into account.

What about salt water or fresh water?
What about water temperature?

The WSSRC is a "exclusive Boys club" and unless you've got a fat wallet your not welcome!!

Hey choco, which event was that? In all the time the Sandy Point Sailboard Club ran speed events we never adjusted for tidal effect. (1990- 1996 as far as I can remember)

Your last comment about the WSSRC seems pretty right.

sailquik said...
Oh Mathew! LUBRICATING, BUBRICATING!

I first read that as boobricating... *sigh*.

What a load of semantic nonsense. Lubrication is totally irrelevant to what defines sailing because.....it just IS! Of course water 'lubricates'. It lubricates the hull of any craft against..... well everything, including the other water it sails on/in.

The dead downwind argument is another furphy. Going dead downwind is drifting, not sailing. No speed records are ever set 'drifting', mainly because things can only drift at some speed considerably slower than the wind speed. Sailing is using the forces between water and wind to 'sail', not drift, and this entails going at some vector across the direction of the wind and that necessitates the sideways resistance of some type of foil. After all, 'things' can 'drift' all on their own. It requires no helmsman and no use of 'sailing' technology.

Sailing technology would be anything that wind can push against, eg: including a cardboard box which wouldn't preclude it from the definition of "sailing" -> you actually can go downwind if you choose too...

If the big boat guys had thought to find a way to take advantage of the 'Ground Effect' years ago, they would have and it would have not raised and eyelid. (Hmmm, I wonder about Longshot in 'The Canal'?

They did make use of "ground effect" -> its called planing *. The effect-from-the-ground that I am talking about is something entirely different, which is why I am highlighting "lubrication" and not "lift".

I find it very Sus' that a syndicate that is aiming at developing a supercavitating foil to drastically reduce drag is actually bleating about others possibly using 'Ground Effect'. Lets see now....supercavitating. Isn't that where the lifting foil runs in a bubble of AIR!!!! Not water, AIR. Is that sailing???? in water?

The bubble will most likely contains air that was previously dissolved in the surrounding water - so depending on your definition of "water", yes or no... ie: if water has air in it, is it... "water"?

It may also contain steam depending on the vaporisation point.

Utilizing 'ground effect' is just another different way to reduce drag when sailing in water (do I have to list all the other ways people have found to do exactly that again?).

There is no argument. It is sailing by any logical definition. Anything else is pure sour grapes and vested interest.

Skim boarding specifically only works in shallow water depths as the skim effect is greatly reduced in deeper water. ie: the general recommendation for water depth is 3 inches (http://www.howtoskimboard.com/category/thebasics). **

Sure "ground effect" is allowed to be used, but that is something different to lubricated sand. And I'm not arguing that there isn't a vested interest, as 50cm appears to be 'too deep' - given that skim boards dont work very well in deep water, one would think that 4-6 inches (10-15 cm) would be the ruling for minimum depth.

* see en.wikipedia.org/wiki/Ground_effect_in_aircraft

** And if you really want to go into the maths: skimonline.com/articles/skim_hydrodynamics/581.htm

Hi guys,

so here we go our way:

Dear John, dear Council Members,

we have received your press release with explanations regarding newsletter 155, which doesn’t give us answers to a lot of questions we urgently need clarification about.

The rule itself as well as the proceedure by which the rule was implemented without consideration for its implications still lead us to the assumption, that the WSSRC is not following the basic principle of equal treatment of all sailing vessels anymore, effectively excluding windsurfers and kiteboarders from serious attempts to break the outright speed sailing record on previously approved, natural venues.

We do not oppose discussion about the development of the existing and future rules, but a rule with such wide implications needs to follow at least a proper evaluation including communication and consultation with the most affected parties.

If the WSSRC continues to ignore us, as legitimate representatives of the vast majority of approximately 2000 potential record contenders as well as of the affected classes, we will be forced to install a new, independant speed record council, borne by the classes themselves.

We still hope that the intention of the WSSRC is to ensure fair play between all interested parties and not to protect personal interests of individual record contenders. It is not too late yet.

We kindly request you to immediately withdraw the changes to rule Nr. 3 and start open talks with us, represented by interim spokesman Martin van Meurs, before Monday, 07.07.2008 12:00 GMT, otherwise we are forced to start up preparations and form a new council with all consequences.

Best regards,
Markus Schwendtner