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.