toad wrote:
Care to explain why a windmill which is capable of powering itself
forward against it's own drag can only do it with a true wind? How
does it know if the wind it is 'feeling' is true or not, it has no
concept of true wind which is merely the wind speed and direction at
an arbitary stationary point.

I thought we'd done this to death.

Don't think force, think energy. Imagine the boat is still, the wind is
blowing over it, and the mill is connected to a winch to a fixed point.
There will be a level of gearing low enough somewhere, so that the
boat can wind itself forward against the winch.

As you increase the gearing, you will increase the amount of power
needed to drive the winch. (not the torque, AKA force, but the POWER).

As you increase the speed of the winch with more gears you will need
more and more power.

Be careful when you crunch the numbers on this. Drag from the mill is
proportional to the square of the apparent wind, power proportional to
its cube, and power to propel the boat proportional to boat speed times
drag. If you forget hull and aerodyamic drag and transmission losses
you can fool yourself into thinking the boat *will* keep accelerating
forever. Even so, if the true wind is zero you get no excess of power
whatever you do.

This is from an Excel spreadsheet.

Real Wind-- 10
Boat Apparent req'd Avail. Excess
speed Wind Drag power power Power (%)
1 11 121 121 1331 1000%
2 12 144 288 1728 500%
3 13 169 507 2197 333%
4 14 196 784 2744 250%
5 15 225 1125 3375 200%
6 16 256 1536 4096 167%
7 17 289 2023 4913 143%
8 18 324 2592 5832 125%
9 19 361 3249 6859 111%
10 20 400 4000 8000 100%

100 110 12100 1210000 1331000 10%


If I reset the real wind to zero, all the excess power figures go to
zero - which implies zero losses in the system.

To make it easy for anyone else, the formulae on the "9" line of that read:
=A11+1
=A12+B$1
=B12*B12
=C12*A12
=C12*B12
=(E12-D12)/D12

Andy

On 14 Oct, 16:52, Andy Champ wrote:
toad wrote:
Care to explain why a windmill which is capable of powering itself
forward against it's own drag can only do it with a true wind? How
does it know if the wind it is 'feeling' is true or not, it has no
concept of true wind which is merely the wind speed and direction at
an arbitary stationary point.

There will be a level of gearing low enough somewhere, so that the
boat can wind itself forward against the winch.
Even so, if the true wind is zero you get no excess of power whatever you do.

How does the windmill know the wind is not true wind? It has no
concept of 'true' wind, it lives exclusively in apparent wind.

Assume the windmill direct into wind concept works:

You can take your windmill cart, put it on another cart and tow it at
20kts. It sees 20kts and will move forwards along its cart. If you
stop the cart and blow 20kts at the windmill cart it will move
forwards at exactly the same speed.

In other words there is some spare energy left over to drive the cart
forwards after the energy required to hold the windmill in equilibrium
with the wind is expended. In my example above that spare energy is
used to drive the cart forwards but in your example of the windmill on
the foredeck that surplus energy can be used to save petrol.

Now we both accept that idea is laughable so you have to explain why
it's not laughable when the wind blowing is caused by nature.

....but most importantly, why oh why oh why doesn't someone just post
the mathmatical proof, the last time this came up I said I'd leave the
thread 'till proof turned up and none did. Odd that.

toad wrote:

How does the windmill know the wind is not true wind? It has no
concept of 'true' wind, it lives exclusively in apparent wind.

Most amusing that you call me a troll for pointing out that this also
applies to motor sailers.

On 14 Oct, 19:14, (Steve Firth) wrote:
toad wrote:
How does the windmill know the wind is not true wind? It has no
concept of 'true' wind, it lives exclusively in apparent wind.

Most amusing that you call me a troll for pointing out that this also
applies to motor sailers.

You claimed the apparent wind on boat motoring in a flat calm would
not be on the nose.

Like saying that if I sit on a motorway in a convertable the wind
blast will be coming from the left!

On 14 Oct, 19:14, (Steve Firth) wrote:
toad wrote:
How does the windmill know the wind is not true wind? It has no
concept of 'true' wind, it lives exclusively in apparent wind.

Most amusing that you call me a troll for pointing out that this also
applies to motor sailers.

But you seem to be claiming that a sail can produce forward force from
a headwind. It's obvious how a windmill might do that, but a
sail ... ?

Ian

"Ian" wrote in message
oups.com...
On 14 Oct, 19:14, (Steve Firth) wrote:
toad wrote:
How does the windmill know the wind is not true wind? It has no
concept of 'true' wind, it lives exclusively in apparent wind.

Most amusing that you call me a troll for pointing out that this also
applies to motor sailers.

But you seem to be claiming that a sail can produce forward force from
a headwind. It's obvious how a windmill might do that, but a
sail ... ?

Ian


The sailboat does go forward doesn't it? (Hint: break down the vectors)

I trust you studied my numbers?

toad wrote:

How does the windmill know the wind is not true wind? It has no
concept of 'true' wind, it lives exclusively in apparent wind.

It doesn't know the difference.

Assume the windmill direct into wind concept works:

You can take your windmill cart, put it on another cart and tow it at
20kts. It sees 20kts and will move forwards along its cart. If you
stop the cart and blow 20kts at the windmill cart it will move
forwards at exactly the same speed.

Same speed *relative to the the surface it is on*.


In other words there is some spare energy left over to drive the cart
forwards after the energy required to hold the windmill in equilibrium
with the wind is expended. In my example above that spare energy is
used to drive the cart forwards but in your example of the windmill on
the foredeck that surplus energy can be used to save petrol.

Now we both accept that idea is laughable so you have to explain why
it's not laughable when the wind blowing is caused by nature.

...but most importantly, why oh why oh why doesn't someone just post
the mathmatical proof, the last time this came up I said I'd leave the
thread 'till proof turned up and none did. Odd that.


Lets take this step by step.

Do you accept that it is possible for the cart to move directly upwind?

Andy.

On 14 Oct, 19:38, Andy Champ wrote:

Same speed *relative to the the surface it is on*.

Yes, so you accept it has spare energy left over after it has overcome
the drag of the windmill. So the windmill on the foredeck of our power
boat has enough energy to push against the wind pushing back on it. It
also has enough energy left over after this to move it forwards.

Which means you can gear that spare energy to the engine and save some
petrol.

Yet you and I both accept you can't do that.

So there's a paradox.

In other words there is some spare energy left over to drive the cart
forwards after the energy required to hold the windmill in equilibrium
with the wind is expended. In my example above that spare energy is
used to drive the cart forwards but in your example of the windmill on
the foredeck that surplus energy can be used to save petrol.

Now we both accept that idea is laughable so you have to explain why
it's not laughable when the wind blowing is caused by nature.

...but most importantly, why oh why oh why doesn't someone just post
the mathmatical proof, the last time this came up I said I'd leave the
thread 'till proof turned up and none did. Odd that.

Lets take this step by step.

Or to put it another way "Lets take this step by step so I can keep
talking rather than posting the maths that I claim is simple to prove
my case."

Do you accept that it is possible for the cart to move directly upwind?

It is essential that we assume that to be the case so you can explain
the paradox exposed by the windmill on powerboat example.

If in a headwind the windmill pushes back harder than it is pushed
then it must do that no matter how that headwind comes about. Which
leaves us with a power boat with a windmill on it's foredeck getting a
net gain in energy from wind that it is creating.

On Sun, 14 Oct 2007 11:57:47 -0700, toad
wrote:

On 14 Oct, 19:38, Andy Champ wrote:

Same speed *relative to the the surface it is on*.

Yes, so you accept it has spare energy left over after it has overcome
the drag of the windmill. So the windmill on the foredeck of our power
boat has enough energy to push against the wind pushing back on it. It
also has enough energy left over after this to move it forwards.

Which means you can gear that spare energy to the engine and save some
petrol.

Yet you and I both accept you can't do that.

So there's a paradox.

In other words there is some spare energy left over to drive the cart
forwards after the energy required to hold the windmill in equilibrium
with the wind is expended. In my example above that spare energy is
used to drive the cart forwards but in your example of the windmill on
the foredeck that surplus energy can be used to save petrol.

Now we both accept that idea is laughable so you have to explain why
it's not laughable when the wind blowing is caused by nature.

...but most importantly, why oh why oh why doesn't someone just post
the mathmatical proof, the last time this came up I said I'd leave the
thread 'till proof turned up and none did. Odd that.

Lets take this step by step.

Or to put it another way "Lets take this step by step so I can keep
talking rather than posting the maths that I claim is simple to prove
my case."

Do you accept that it is possible for the cart to move directly upwind?

It is essential that we assume that to be the case so you can explain
the paradox exposed by the windmill on powerboat example.

If in a headwind the windmill pushes back harder than it is pushed
then it must do that no matter how that headwind comes about. Which
leaves us with a power boat with a windmill on it's foredeck getting a
net gain in energy from wind that it is creating.

No it gets energy from a reduction of the kinetic energy of the _true_
wind.

On 15 Oct, 19:17, Goofball_star_dot_etal
wrote:
On Sun, 14 Oct 2007 11:57:47 -0700, toad
wrote:





On 14 Oct, 19:38, Andy Champ wrote:

Same speed *relative to the the surface it is on*.

Yes, so you accept it has spare energy left over after it has overcome
the drag of the windmill. So the windmill on the foredeck of our power
boat has enough energy to push against the wind pushing back on it. It
also has enough energy left over after this to move it forwards.

Which means you can gear that spare energy to the engine and save some
petrol.

Yet you and I both accept you can't do that.

So there's a paradox.

In other words there is some spare energy left over to drive the cart
forwards after the energy required to hold the windmill in equilibrium
with the wind is expended. In my example above that spare energy is
used to drive the cart forwards but in your example of the windmill on
the foredeck that surplus energy can be used to save petrol.

Now we both accept that idea is laughable so you have to explain why
it's not laughable when the wind blowing is caused by nature.

...but most importantly, why oh why oh why doesn't someone just post
the mathmatical proof, the last time this came up I said I'd leave the
thread 'till proof turned up and none did. Odd that.

Lets take this step by step.

Or to put it another way "Lets take this step by step so I can keep
talking rather than posting the maths that I claim is simple to prove
my case."

Do you accept that it is possible for the cart to move directly upwind?

It is essential that we assume that to be the case so you can explain
the paradox exposed by the windmill on powerboat example.

If in a headwind the windmill pushes back harder than it is pushed
then it must do that no matter how that headwind comes about. Which
leaves us with a power boat with a windmill on it's foredeck getting a
net gain in energy from wind that it is creating.

No it gets energy from a reduction of the kinetic energy of the _true_
wind.

To the windmill there is no difference between wind powered by the sun
(in your terms true), or wind created by the diesel of the engine. (in
your terms apparent).

If I put a windmill in a 20kt wind and it makes 1kw, I can put the
same windmill on a powerboat on a still day at 20kts and it will still
make 1kw.

Now if that 1kw is enough to push the windmill forward against the
wind then that energy surplus will also exist for the windmill on the
power boat so if you gear it to the prop shaft, after the drag of the
windmill has been equalized, there will be some power left over to
save some diesel. This is patently absurd so if you buy the idea the
windmill boat/cart can drive forward into wind you have to explain
this paradox away or explain how 20kts of wind created by diesel is
different to 20kts of wind created by the sun.

Anyway, I'm going to do what I did last time and ignore this thread.

I'll revisit the thread in a few days time and if someone has posted
the correct equations and worked it through with figures to show the
windmill cart/boat can move directly into wind I shall post to
acknowledge my acceptance that it is possible. Otherwise, I shall post
nothing.