Wilbur:

Obviously from reading this thread it seems that there are enough boaters
who believe this BS. If you write ad copy and more than 50% of the readers
believe it, then it is good copy. However, that doesn't make it right.

David

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

"Steve Firth" wrote in message
...
toad wrote:

On 14 Oct, 14:17, Andy Champ wrote:

An apparent wind from dead ahead can add nothing but a force directly
astern.

The case where a true wind from ahead can be used to drive a windmill
that can drive a propeller to propel the vessel is different; but this
requires a true wind.

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.

As far as the windmill is concerned it has a 20kt headwind and
(alledgedly) it can take that energy, use some of it to hold itself
stationary against the wind and _still_ have surplus energy to drive
forwards. If it can do that you could gear it to the engine of the
20kt powerboat and save petrol equivalent to the surplus power that is
left over once you subtract the energy required to overcome the
windmill's own drag from the total energy harnessed by the windmill.

MY recollection of this is that with a windmill it's simply not possible
to reduce the drag sufficiently to get a sufficient energy to make it
useful. Wingsails are much better at it or even even proeprly trimmed
sails.

ASCII news isn't the best medium to get the point across, but I'll try.

If one is motoring in a calm on a flat millpond then there is an
apparent wind equal to the speed of the boat from dead ahead. Hoist a
sail and you can make no use of that wind, agreed. However that only
applies if you maintain the same course. Now do what any sensible bloke
would do and adjust your course to make use of the wind as well as the
motor.

Doesn't the wind still appear to come from dead ahead? Or does your motion
cause the wind to blow?

You now have wind in your sails and you still have an apparent
wind. If you look at the force triangle there is still a component from
the apparent wind.



No doubt the craptain also doesn't beleive in back EMF or any of the
other phenomena which appear to produce "something from nothing"

Back EMF actually works to negate the driving field to zero or to its
initial condition. It's more like "nothing from something".


however
it's not the case that something is being produced from nothing and in
this case the extra energy is achieved at the usual expense of not being
able to sail directly into the apparent wind.

Yes, and the extra energy from back EMF is not usuable either because it is
cancelling the driven field. With logic like yours we are only steps away
from perpertual motion. Just think of all the extra energy generated by
friction - it's "free energy", if only we can redirect it along the applied
force we would have all the energy problems solved. Perhaps if one runs or
drives in a zig-zag or back and forth motion we can trick friction into
going in our favor - just like you do with apparent wind in sails. You whole
argument and reasoning is just that - wind in sails.

Wilbur Hubbard's mind is not cluttered with useless memorized facts or
dimmed with fuzzy thinking. Basic principles and a strong application of
rigorous logic brings correct and defendable conclusions.

Does a properly designed sailboat keel provide forward lift? Same thing?
Gordon

"Gordon" wrote in message
...

Does a properly designed sailboat keel provide forward lift? Same
thing?
Gordon

Read this about lift:

http://home.hccnet.nl/m.holst/LiftDrag.html

Particularly the part about "by definition lift does NOT do work".

Bill wrote:

Perhaps if one runs or drives in a zig-zag or back and forth motion we can
trick friction into going in our favor

Umm well we can, water can be made to flow up hill on a slope.

http://www.livescience.com/environment/060329_water_uphill.html

http://www.telegraph.co.uk/earth/mai...07/10/05/sciwa
ter105.xml

Wilbur Hubbard's mind is not cluttered with useless memorized facts or
dimmed with fuzzy thinking.

The Craptains mind is untroubled by thought of any kind.

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.

"Andy Champ" wrote in message
...
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

I hope for your sake you are trolling, joking or both.

On Sun, 14 Oct 2007 15:28:23 +0100, (Steve Firth)
wrote:

o doubt the craptain also doesn't beleive in back EMF or any of the
other phenomena which appear to produce "something from nothing" however
it's not the case that something is being produced from nothing and in
this case the extra energy is achieved at the usual expense of not being
able to sail directly into the apparent wind.

I believe in entropy. The so called extra energy comes directly from
the thrust bearing of the engine, and it will drink more with a sail
developing lift. I don't necessarily say there is no benefit to having
a sail up. Lift means drag. The ratio, in an airplane, is equal to the
glide angle. The longer and skinnier the wing the better it will
glide. There is a name for that, aspect ratio. Generally low for
sails. My father had a gaff rigged schooner: now there is real low.

Casady

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.