That's because it's in the *data*, not in the narative. In that article they are generically discussing iceboat performance and they include GPS plots from boats negotiating a closed course with known wind data. The GPS plot demonstrate their downwind course speed.
I looked for, but couldn't find the data, only a statement that someone said it is available, but no link. Do you have a link?
BubbleBoy wrote:
There's no "OMG, our VMG is higher than the wind -- it's old hat to them. Do the math on the GPS plots and you have your evidence.
Link?
BubbleBoy wrote:
You continue to make the same assertion over and over, but you do so *without* examining the data. Why not do the math yourself and THEN argue the point?
Link?
BubbleBoy wrote:
A: Of course there are "pavement currents" ... the pavement moves pretty darn fast at the equator doesn't it now.
BubbleBoy wrote:
B: I matters not a whit whether there are currents or not. It's long been established that there is no way to discern if the pavement is moving and the air is still, or the pavement is still and the air is moving. We simply can't tell, and it absolutely doesn't matter
Both of the above points are completely consistent and relevent to the nil-wind sail boat in the current. It's two mediums moving relative to each other. It matters not which is actually "moving", and additionally, you can't tell which is actually "moving". That's the point of the brainteaser.
The above "frame of reference" point is one of the fundamentals of basic physics.
The boat/wind/current has a 3rd frame of reference not available to the land-yacht, or DWFTTW device.
There is a Boat(1) in Nil Wind(2) with a 5kt Current(3) moving it towards ( or away from) the land(4) the ultimate speed is being measured between the boat(1) and the land(4)
Our Land Yacht(1) on the pavement in Nil Wind(2) with a 0kt Pavement Current(3) moving it towards (or away from ) say some mountains?( 4)
The Water in the Ocean and the Land are not moving in the same current.
The Pavement and the Mountains are both moving in the same current,
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but it is possible to tell if something is rotating
You speak the truth. Rotation and acceleration are absolute. Velocity is relative.
Dawson wrote:
The boat/wind/current has a 3rd frame of reference not available to the land-yacht, or DWFTTW device.
Not true. And I'd be happy to describe it to you on the Mythbusters forum. Why is no one willing to have the discussion where it might yield a really nifty segment, and proof one way or the other?
Quote:
the ultimate speed is being measured between the boat(1) and the land
There's no more reason to drag the land into this than there is to drag the sun or moon into it.
When I first hear of this discussion I was picturing a sail boat going straight downwind, in which case, best case you get wind speed,
However that is missing a beautiful point
Lets say our reference frame is the ground, and in our reference frame the wind is blowing west at 10 mph
A boat has a heading of 60 degrees with this, and its "downwind" component is 10 mph, that is 10 mph heading east in our frame of refereance, that means in our frame of reference is south componet is 17.3. Now if you add up all the vectors you see that if you shift your frame of reference to the boat, you would now say the wind is blowing south at 17.3 mph
Uh oh... I just started thinking about a ................. --- a gravity slingshot, _________________ TSA, DHS, NDAA and SOPA Seig Heil!
Lets say our reference frame is the ground, and in our reference frame the wind is blowing west at 10 mph
A boat has a heading of 60 degrees with this, and its "downwind" component is 10 mph, that is 10 mph heading east in our frame of refereance, that means in our frame of reference is south componet is 17.3. Now if you add up all the vectors you see that if you shift your frame of reference to the boat, you would now say the wind is blowing south at 17.3 mph
True. But that only gives a downwind velocity component equal to the wind speed. It's possible to do far better than that.
I was just showing how windspeed can vary greatly between reference frames
in addition, its easy to see in the above example that the boat is is doing 20 mph at 150 degrees, now reversing tack it will pass a point that it is doing 20mph due east(stright downwind to the man on shore) , now say it continues until it has fully reversed its tack, to 30 degrees heading, and the same 20 mph, it now has a "downwind" component of 10mph windspeed, but its "downwind component" has varied from 10-20mph and back to 10, its average is better then the downwind, reversing this and optimizing your tack angels and its easy to see your downwind component can never be less then the "true windspeed" and hence your average downwind component must be greater then the windspeed
thus you have gone downwind faster then the wind
and if you are trying to say that this isn't going "straight down wind faster then the wind" well, thats an easy thing to fix, create two of them, and mechanically link them together, on rails, your two boats are now more like pistons, in a boxer engine, they move away from each other then towards each other, and the whole contraption is going from windspeed to faster then windspeed, to windspeed, averaging better then windspeed, going directly downwind
even better you could put several of these boats on two counter rotating eliptical tracks, and the contraption could achieve a constant speed downwind faster then the wind , where each boats track would comprise an s parrelel to the direction of travel, _________________ TSA, DHS, NDAA and SOPA Seig Heil!
Last edited by Jason on Tue Oct 14, 2008 4:29 am; edited 3 times in total
When I first hear of this discussion I was picturing a sail boat going straight downwind, in which case, best case you get wind speed
With just sails, yes. But if you have a propeller in the airstream and another propeller in the water, and they have different pitches (or are connected via a non 1:1 gearbox), then you can go faster. Same idea as with the land device, the water prop extracts energy from the water passing under the boat, and transfers it to the air prop that drives the boat forward. And with suitable pitches/gearing, you can also "sail" straight upwind, where a pure sailboat would be "in irons". _________________ H4 + various skills (only foot-launch so far)
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DWFTTW is in effect a wind powered vehicle going into a headwind, this has been doing by sail boats since the invention of sailboats, and that goes back at least a thousand years, its nothing new _________________ TSA, DHS, NDAA and SOPA Seig Heil!
DWFTTW is in effect a wind powered vehicle going into a headwind, this has been doing by sail boats since the invention of sailboats, and that goes back at least a thousand years, its nothing new
Actually, I think it was a long time before sailboats were able to tack into the wind. I think the early ones were only able to aim at various directions downwind.
you are probably right that after the invention of sailboats it took some time to master sailing, but it was definitely understood in the Times of Magellion, Columbus etc, and thats looking back 500 years _________________ TSA, DHS, NDAA and SOPA Seig Heil!
Horizontal spars were attached to the mast, and the top and bottom of the sail was attached to the spars. The spars could be turned around the mast to provide some ability to maneuver the boat across the wind or slightly upwind.
I looked for, but couldn't find the data, only a statement that someone said it is available, but no link. Do you have a link?
Some months ago while on another forum, I downloaded the XLS file accompanying that article (they reference the file several times in the article). Like you , currently I can't fine the link to the associated data, only the article and the charts. To test the data, I charted the data on Excel and produced a chart that was indentical to the one displayed in the article. Sorry for sending you on a goose chase for the data that I now cannot find -- I have sent an email to the NALSA and I'll let you in on the results.
However -- again, unless you are accusing the NALSA of posting bad data, the chart displayed in that article is an actual shot of the chart plotted from the data. The grid scale is state to be the same in x and y so if the grids look square on your screen you're in the money. (I have posted the chart below).
10mph wind, ~45 degree downwind tack (you can hold a protractor between the angles if there are any doubts). In short order you see that in their racing craft, they are getting 3x+ the VMG of the wind on the downwind leg.
Addionally here is a quote from the FAQ section of the website:
Quote:
"The slowest point of sail for a landyacht is dead down wind when it sails a little slower than the wind speed. By sailing at 45 degrees off directly down wind the yacht can sail much faster than the wind. The 'velocity made good' down wind is often over twice as fast as sailing directly down wind."
Again, I'll update as soon as I get a response to my email from the NALSA, but it's not hard to see from the data and their own FAQs where this is going to end up.
I know you are among a large crowd who say it's impossible, but it just ain't so.
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