Sailing downwind - faster than the wind?

[mikemonty]

Only for people with poor comprehension skills and there is little I can do about that.

Actually, the last time I was tested, for a high-level management position, I scored in the top 10% of the population for what was effectively a language and comprehension test.

And you have not addressed the point where I illustrated that you made the implication.

My comprehension skills say that tells me a lot.

I think the problem is yours, despite your trying to deflect - you must be a great teacher.

 

[fireball]

Stop your bleedin crappy argument over who said/implied whatever and go back to the original subject matter PLEASE!

Kids these days!

 

[fireball]

SL - I've just looked at the Roller under the Ruler video and I'm struggling with the WHY ...

I see that with a fixed flywheel (the big blue wheel) and draw a ruler over it will turn the wheel - but with a L2R move of the ruler the wheel will turn Clockwise ....
Take that fix off and do it again - the Wheel will still turn clockwise and move in the direction of the ruller
Now put the wheel on rollers and the wheel starts to turn the otherway ... why?!

 

[RAI]

SL - I've just looked at the Roller under the Ruler video and I'm struggling with the WHY ...

I see that with a fixed flywheel (the big blue wheel) and draw a ruler over it will turn the wheel - but with a L2R move of the ruler the wheel will turn Clockwise ....
Take that fix off and do it again - the Wheel will still turn clockwise and move in the direction of the ruller
Now put the wheel on rollers and the wheel starts to turn the otherway ... why?!

Gear ratios.

 

[fireball]

Sorry - 'Gear Ratios' does nothing to explain why the flywheel turns in the opposite direction ....

 

[RAI]

Sorry - 'Gear Ratios' does nothing to explain why the flywheel turns in the opposite direction ....

Because the frictional force on the bobbins on the table has greater leverage than the frictional force of ruler on the big blue wheel.

 

[fireball]

Ah - ok ... thank you ... beginning to understand it now.

 

[DJE]

Ah - ok ... thank you ... beginning to understand it now.

Does this help?

 

[pmagowan]

Snow Leopard I am afraid you haven't got where the impossible contingent have come from. It is not the gearing or the mechanics that are wrong it is the fundamental. You could have wind powered lasers and super cooled magnets but it still would be impossible.

A vehicle powered by the wind can not move directly downwind faster than the wind over a fixed time. The interesting use of relativity to prove it is possible just shows a lack of understanding. It does not matter if you look at thinks relative to the vehicle, relative to the ground or relative to the wind. What seems the be happening from the posible contingent is you start off relative to the vehicle and then switch to relative to the ground and you think you have found a new energy source. Since the only energy entering the system is wind all the energy in the system comes from the wind. This means if you add all the energy in the system together the number will be equal to the wind energy. Your system would have the number being greater than the wind energy which is the equivalent of stating that 2 is equal to 3 in mathmatics. This is not just a wee arguable point in physics this is a fundamental rule as if it were not true nothing would make sense. A number can not be larger than itself!

 

[fireball]

Ok then - how does the demonstration work then?

 

[Pierrome]

Since the only energy entering the system is wind all the energy in the system comes from the wind. This means if you add all the energy in the system together the number will be equal to the wind energy.

No. The energy does not come from the wind. Wind does not have any energy of itself.
Energy comes from the DIFFERENCE between the ground and the air velocity. If the cart is travelling at windspeed, the energy is still there in the movement of the ground.

You got to ask yourself how is moving air - stationary ground (as in the Goodman outdoor cart) different from moving ground stationary air (as in the treadmill test) - there is no difference! As I said before, if there was a difference all wind-tunnel testing of aircraft would be invalid. +

 

[Kelpie]

A vehicle powered by the wind can not move directly downwind faster than the wind over a fixed time.

Do you accept that it is possible to tack downwind faster than the wind?

 

[RAI]

A vehicle powered by the wind can not move directly downwind faster than the wind over a fixed time.

How does BMW Oracle do it then? I did it for over an hour on the down-wind leg, covering 20 nm down wind in 6-8 knots of wind.

Since the only energy entering the system is wind all the energy in the system comes from the wind.

So how much energy is there in the wind? Certainly enough. It's how the energy is captured and converted into speed that is the issue.

 

[snowleopard]

A vehicle powered by the wind can not move directly downwind faster than the wind over a fixed time./QUOTE]

If you accept that BMW Oracle can achieve 3 x wind speed VMG downwind by tacking, let's take it one stage further. We to tow a waterskier behind the boat on a long rope. he maintains a straight course as the towing vessel tacks either side of the rhumb line so he again is travelling straight downwind. at 18 knots in 6 knots of wind.

That show one way of achieving the desired effect. The videos show it being done too. So clearly it is not impossible. We are not claiming it is the laws of physics are wrong but the way they are being applied to this problem by those who are saying it is impossible.

 

[Ubergeekian]

Snow Leopard I am afraid you haven't got where the impossible contingent have come from. It is not the gearing or the mechanics that are wrong it is the fundamental.

No.

Since the only energy entering the system is wind all the energy in the system comes from the wind.

No. You're just wrong. The way in which you are just wrong has been pointed out several times by several people.

 

[nmeyrick]

No. The energy does not come from the wind. Wind does not have any energy of itself.
Energy comes from the DIFFERENCE between the ground and the air velocity. If the cart is travelling at windspeed, the energy is still there in the movement of the ground.

You got to ask yourself how is moving air - stationary ground (as in the Goodman outdoor cart) different from moving ground stationary air (as in the treadmill test) - there is no difference! As I said before, if there was a difference all wind-tunnel testing of aircraft would be invalid. +

I've been reading this all with interest and am wary of entering the fray, but I think that the comments above clearly illustrate the flaw in this argument.

Yes, I agree that a vehicle can travel directly downwind faster than the wind - Sunseeker anybody? But this was not the question. The blog to which the OP refers poses the questions as "Can a vehicle be built which can go directly downwind, faster than the wind, powered only by the wind(DDWFTTW), steady state?"

This is where the problem enters. Yes there is relative motion between the vehicle and the road. Yes this could be used to turn the wheels and, via a gearing to drive a prop. But the relative motion is the result of the vehicle's kinetic energy, and since the vehicle is powered only by the wind, its kinetic energy comes from the wind.

You are claiming that the wind makes the vehicle move, which turns the wheels, which powers the vehicle. That is perpetual motion. If the vehicle is moving faster than the wind it is because there is another source of energy input into the system, which could be from a driven belt, or potential energy being released as it moves down a gradient, or even cold fusion. But it aint being powered only by the wind.

Of course if the team have indeed got this worked out it will be a significant breakthrough, and I look forward to reading about it in a peer reviewed journal. But for now please forgive my skepticism if I do not take a few grainy videos on youtube as definitive proof of anything.

Toodloo

 

[Kelpie]

A vehicle powered by the wind can not move directly downwind faster than the wind over a fixed time./QUOTE]

If you accept that BMW Oracle can achieve 3 x wind speed VMG downwind by tacking, let's take it one stage further. We to tow a waterskier behind the boat on a long rope. he maintains a straight course as the towing vessel tacks either side of the rhumb line so he again is travelling straight downwind. at 18 knots in 6 knots of wind.

That show one way of achieving the desired effect. The videos show it being done too. So clearly it is not impossible. We are not claiming it is the laws of physics are wrong but the way they are being applied to this problem by those who are saying it is impossible.

That's an excellent way of explaining it, SL.
Personally, I retain some doubts as to what is being shown in the videos. But in principle you cna get downwind faster than the wind, without brekaing the laws of physics. I presume the 'secret' is that the tips of the prop are travelling in a helical pattern which you could view from above and sketch out as a zig-zag- exactly the same as tacking downwind.

 

[pmagowan]

No. The energy does not come from the wind. Wind does not have any energy of itself.
Energy comes from the DIFFERENCE between the ground and the air velocity. If the cart is travelling at windspeed, the energy is still there in the movement of the ground.

You got to ask yourself how is moving air - stationary ground (as in the Goodman outdoor cart) different from moving ground stationary air (as in the treadmill test) - there is no difference! As I said before, if there was a difference all wind-tunnel testing of aircraft would be invalid. +

Wind is what we call it when there is a difference between air and ground velocity. Most people take the ground velocity to be zero for the purposes of simplicity. The moving air (or wind as it is popularly called) is the energy source. We can get in to the nitty gritty of gas dynamics but it is irrelevent. The wind is the power source. When something is blown along the ground energy has been imparted to it by the wing. The fact that the ground now appears to be moving has nothing to do with it as it is the wind power which makes this happen. You are simply changing your point of reference. To extract energy from the now moving ground is the same as to extract it directly from the wind except less efficient. You will create drag and slow the vehicle.

The people who talk about tacking are discussing another point and since this simple one is causing difficulty I don't see any cause to widen the subject. And propeller blades don't tack.

This has just got to be a troll. I note in the other poll someone has made the link to April 1st- this to me is the most likely. I quite like trolls though, they are fun.

 

[fireball]

<snip>
The people who talk about tacking are discussing another point and since this simple one is causing difficulty I don't see any cause to widen the subject. And propeller blades don't tack.

This has just got to be a troll. I note in the other poll someone has made the link to April 1st- this to me is the most likely. I quite like trolls though, they are fun.

But the propeller is moving across the wind is it not? It isn't moving with the wind (ala paddlewheel) ... and as one is moving across one way the otherone is moving across the otherway ... so countering any sideways thrust ... therefore all thrust is directed forward no? It does look like tacking ... just with 2 boats ..

as for 1st April ... maybe - I don't know - if I did I'd be a Physics Professor ... but I'm not ...

 

[pmagowan]

But the propeller is moving across the wind is it not? It isn't moving with the wind (ala paddlewheel) ... and as one is moving across one way the otherone is moving across the otherway ... so countering any sideways thrust ... therefore all thrust is directed forward no? It does look like tacking ... just with 2 boats ..

as for 1st April ... maybe - I don't know - if I did I'd be a Physics Professor ... but I'm not ...

If the propeller blades all wizzed off in their various directions then they are just small sails. If they are attached to a moving vehicle being proppelled directly downwind then, as has been said on numerous occasions, when the apparent wind hits close to zero they will stop as no air is being driven through them to 'propel' them.

I understand that this is not the method being proposed as the wheels and stuff is involved but as per my previous post this is irrelevent and would only cause the prop to slow quicker.

It is like driving a car with a preset fuel consumption on a flat surface. It will reach an equilibrium at a certain speed. Ahh, but the ground is moving relative to the vehicle so if we lower a little wheel on to it with a dynamo attached we could get energy from this to make the car go faster??? No you can't, drag slows car, energy gained must be less than energy lost (law of conservation of energy) ergo car slows. The fuel in the previous scenario is wind.

Nice little thought puzzle tho!