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.

On Mon, 15 Oct 2007 13:00:43 -0700, toad
wrote:

On 15 Oct, 19:17, Goofball_star_dot_etal
wrote:

snipped some

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).

ok. By "true" I assume no tide in this case. The frame of reference is
the water and velocities are measured wrt to the water/land


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.

ok.


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

Just a minute.. (k) watts are units of power not energy. If you are to
make sense of this you cannot mix your units and dimensions of force,
energy, power, momentum etc. It might sound pedantic but it is
absolutely fundamental that the dimensions on each side of an equasion
match


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.

Assuming no wind in this case, the affect of driving this windmill
forward will be to increase the velocity of the air from zero to a
finite value. In other words the kinetic energy of the air has
increased, therefore you are doing work not extracting energy, at some
rate. (same units:-) ) You must be losing power.


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


ok, bugger off if you must..


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.

toad wrote:

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

In case you don't, this needs a face to face discussion with drawings
(and possibly beer!). Whereabouts are you?

Andy