Select to expand quotedecrepit said...
[I've found this an interesting topic and have been swayed by both sides of the argument
I's an interesting topic alright. And seeing everyone seems to agree on the facts I'm trying to fathom exactly what the argument is.
Maybe it all boils down to who's going to look after kite surfers. They're too slow to compete with the land and ice sailors who have the advantage of wheels and skates which both resist gravity and provide lateral forces with very little rearward drag - But on the other hand the speed kiters, when they get the critical mass of participants, should, theoretically, blitz deep water sailors who can only overcome gravity by throwing water down into the abyss.
So repeating what we already know another way...
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)
- ie. you gotta produce a downward water momentum mv at a rate equal to the weight of the craft. Doing this while minimising rearward drag is the common challenge.
This equation also applies to the downwash of high flying aeroplanes, helicopters and hovering rockets. So if your board or rig also throws down a bit of air to gain lift it's all the same, it comes out in the wash, it's all fluid dynamics.
Hovercraft and kiters don't have to fully satisfy the equation, it's complicated by the proximity of the bottom - a bit of solid dynamics getting in there.
So if the WSSRC doesn't want to take on kiters, who probably should have a category all to themselves, it's their call. Hope something can get organised to formally recognise the kiter's efforts.
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.
Comparing air ground affect with water ground affect?
Air compresses where as water does not!
Nameless graphs?
This is not enough evidence to ban most of the inshore speed strips in the world!
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?
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!!
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
Chris said: "At the end of the day the argument comes down to whether pushing off the ground through a layer of water with unregulated thickness is sailing."
I don't think there is any doubt about that at all. Looks like sailing to me. I think this is a red herring designed to create an argument and a diversion, and it has been very effective so far.
I find it interesting that syndicates who have spent a lot of money on some other idea to try to get a speed advantage, and then realise they might have more difficulties that they hoped, are in danger of being beaten to the holy grail and are suddenly looking for ways to hobble the opposition.
If the boaties had thought of this in the eighties they would have had another way to hobble windsurfers, and there is no doubt there were many (and still are) that wanted to ban windsurfers from 'world records'.
As long as one is using the water as the medium for lateral resistance, it is 'sailing'. A car on a wet road does not. An ice yacht does not. A land yacht on a wet surface does not. If any of these craft lose their grip on the solid surface they spin out and lose control.
It is the same as finding a clever way to reduce drag by using hydrofoils, or by using a supercavitating foil (is this in the water?) or by using a flying craft where the only contact with the water is a small foil to stop lateral movement (not much different from Slowie on a windsurfer :) ). Some people have found a clever way of reducing drag by sailing in and on a shallow layer of water. Unless they are actually getting physical resistance by digging into the ground, they are sailing.
As I said before. The definition of sailing is self limiting.
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.
Goo Screw: at subsonic speeds air is considered non-compressible, just the same as water.
I think the advantage you get is from the water near the bottom not being able to 'get out of the way' of the new downwash being produced from the board. End plates would make this effect more pronounced, although I wouldn't imagine that the fins on a kiteboard would be big enough to make much of a difference. Could be wrong though.
Ian's formula: Mg = d/dt(mv) shows that the faster you go, the less you have to move the water to support yourself. Prove it next time you're just planing, and compare your rooster tail to when you're really powered up. Fully powered you only ruffle the surface, as opposed to the masses of water movement you get when only just planing. So the faster you go, the less the ground effect will be noticeable.
Nebs, with increasing speed you move less water, but it doesnt mean there are lower forces applied. Nor does it imply the ground effect is going to be any less effective at higher speeds, other than potentially having lower angles of attack on the lifting surfaces. Normally we control the lift with a change in surface area, not AOA on a planing surface (this applies to kite boards too- their trim angles is set by the foils), so the pressure distribution will retain similar characteristics (=> similar ground effect behaviour) at increasing speeds.
So its not only a low speed problem that diminishes with speed.
There are two arguments here that should not be mixed and confused.
1)Whether or not ground effect makes an appreciable difference in shallow water
2)Whether it is unfair to push off a fixed boundary to gain a lift advantage
The effect is clear and demonstrable. So,
1) isnt really an argument any more.
2) comes down to whether you think pushing off a boundary is still in the spirit of the record.
Clearly such decisions have been made in the past, for example, when approached to consider land and ice sailing variants. The WSSRC role is for "sailing" records on water. Same goes for this decision, whether sailing off the ground fits the nature of the class they represent- sailing on water. They dont believe this is the case, and they did some research.
I should add there is a 3rd argument, about whether the 50cm rule is adequate to not exclude those playing in the spirit of the record. This one I'm not so sure about.
Slowie, I guess it comes down to a debate of point no 2, You might be stretching credibilty a little far to suggest that the WSSSCR decision is based on a "belief" that sailing off the ground does not fit the nature of the class they represent-sailing on water, After all in their explanatory note they say
"There was a real concern that unless some sensible ruling was brought in, a world record claim using water only as a lubricant was a possibility. For example, creating a record course by covering a large car park with a plastic sheet and then wetting it to a few mm depth. There was a general feeling that this stretched the aim of breaking records on "water" too far."
Then simply ban sailing on a water lubricated plastic sheet. I'm with Andrew. This is a red herring. And a bad rule even if there is a bonefide need for a rule to prevent "sailing off the ground "as you call it.
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.
Nebs, in your example you arent pushing on 10x the area with 10x speed increase since the planing surface area reduces with speed, so that the total lift remains the same.
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.
[}:)]
Nebbs, some late night reading for you.
ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930084205.pdf
LUBRICATING, BUBRICATING! 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.
LUBRICATING, BUBRICATING!
Hi Matt,Fair enough that you accept there is ground affect in all sailing on water conditions ,but you should start a new thread for your lubrication spiel.
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
