"Ronald Raygun" wrote in message
...
harry wrote:

On 27 Sep, 21:31, Gib Bogle wrote:
On 28/09/2010 5:51 a.m., harry wrote:

An ordinary sail boat can sail faster than the wind without the
benifit of strange turbines.
It's common knowledge to anyone with even a slight knowledge of
physics.
http://en.wikipedia.org/wiki/Sailing..._than_the_wind

Yes, I know about sailing. Did you read the post? Here, I'll cut out
the appropriate part for you, to make it easier:
"A wind powered boat or vehicle that could sail or drive directly into
the wind using a turbine facing the wind to drive a water prop or
wheels"
Do you see the reference to "using a turbine"? OK, now the question is
this: "Can a WIND TURBINE-POWERED vessel or vehicle go faster than the
wind DIRECTLY DOWNWIND?" Think about it.
By the way, a sail-driven craft cannot go faster than the wind DIRECTLY
DOWNWIND either. Get it? Your slight knowledge of physics should be
adequate to grasp this.- Hide quoted text -

Obviously is soon as it went "as fast as the wind downwind" there
would be no wind (relative to the machine/boat etc). Therefore
impossible.

No, that's a faulty conclusion. It correctly answers the wrong question.

The question was whether it is possible for a boat to sail directly
downwind faster than the wind, powered only by a wind turbine. That means
whether it is possible for a boat *to sustain* such a speed.

The question you've answered, however, is whether it's possible for the
boat *to reach* that speed, subject to the constraint that it must start
from rest and only ever head directly downwind whilst accelerating.
That's
a completely different question, doomed to a negative answer by the fatal
constraints imposed.

Anyway, your answer correctly observes that the relative wind speed
approaches zero as the boat's speed approaches that of the wind, and
so the turbine is faced with the impossible task of extracting power
from a dying wind. Therefore crossing the barrier of actual wind speed
is going to be impossible in those circumstances, and in practice there
will be a top speed which it is possible to reach but not exceed.

Suppose this practical top speed is about 90% of wind speed, so that a
10% difference or so is enough to provide the power needed to keep up with
water resistance etc.

But if a 10% difference is enough, then travelling at 110% of wind speed
should also be sustainable.

The only problem remaining is how to reach that state to begin with.
Clearly it can't be done subject to the constraint of your scenario,
but it could be done by other means, including by "cheating" and using
stored energy.

I dare say another way would be to use the wind turbine to accelerate
to beyond wind speed by going downwind *but not directly downwind*, and
then quickly turning directly downwind, relying on inertia to lose not
too much speed in the turn.


Where do the nuts come from?
I bet he has a car that runs on water too.