Here are some comments taken from various newsgroups on why it is "impossible"
for a wind-powered boat to sail directly into the wind.

 

I agree. These "something for nothing" twits have their heads way too
far up their arses. Their main premise seems to be if you use a windmill
you can get enough power out of the wind to overcome the wind. Something
for nothing! Someone asked them why don't they see automobiles with
windmills on top. If their silly thinking is correct all you'd have to
do is get the car going a few mph maybe with battery power and the
apparent wind would start the windmill spinning - then all this extra
energy from the swept area of the windmill would be produced and you
could transfer it to the wheels and the car would go faster and faster
because the wind spinning the windmill would go faster and faster. Sort
of an infinite loop so to speak. Pretty soon you'd have a car going
along at the speed limit and there'd still be excess energy so you'd
have to have some heavy duty brakes engaged at all times in order to not
exceed the speed limit and get a ticket. What a bunch of morons!

Greg

Actually a single mule pulled Erie Canal barges weighing up to 30
tons. But the speed was less than 2 knots and there was no wind or
waves. I'm not saying that windmills cannot move a boat. Only that it
is a complex, impractical means of propulsion for real vessels. Now
if you can show me an example of a windmill moving a 30 foot, 16,000
lb. displacement trawler into the wind at hull speed, I will
certainly reconsider. In fact I will eat plenty of crow if the boat
can be moved at 1/2 hull speed into the wind. But at the moment
windmill power still hovers in that grey zone between theoretical
possibility and practical impossibility.

Very unimaginative sails, even lugsails or sprit sails, do a good job
of propelling a boat off the wind. Years ago I owned a DN iceboat
which could hit speeds of 40 knots in an apparent wind no more than 5
degrees off the bow. For me, the main joy of sailing is its lack of
mechanical complexity.

Larry Z


> It sounds daft, as if it violates _something_, but I'm not sure what.
> Possibly it violates nothing. Boats with standard rigging can tack
> arbitrarily closely into the wind. Weird contraptions, like
> catamarans with independently pivoting hulls, _can_ sail directly into
> the wind. Can this contraption?



In a word, no.

A sail vessel that steer close to the wind, say 15 degrees off axis,
but not directly into it. No matter what the mechanism, sailing
directly into the wind is impossible.


Harry



As for any mechanism that might let you sail directly into
the wind, think about it this way. Instead of still water with
a steady wind, think about a steady current and still air.
Now your question becomes whether or not the boat can move through
that air, along with the current, and experience absolutely
no air resistance. That's obviously not possible. (And the only
other possibility is a sail that generates lift directly into
the true wind.)
--
John Forkosh ( mailto: j...@f.com where j=john and f=forkosh )



Actually Benj, it is you that makes himself appear to be a moron.

I'm simply citing facts. By contrast, you clearly don't understand
even the basic priciples of how a wind powered craft (sailboat)
functions, at least on on a scientific basis.


No wind powered craft can sail directly into the wind, simply because
the physics involved prohibit it. Were a wind powered ship of any
design to attempt to sail directly into the wind, it would go into a
"stall", and the force induced on the craft would drive it backward in
the water.


Learn how sailing vessels operate, and why they need that deep hull or
centerboard in addition to wind to create their mode of propulsion.
It's simple trig and the summation of forces that make the thing move
or point as closely as 15-degees off the direction of the wind. I't
not exactly rocket science!


Idiot.


Harry C.


I somehow completely missed the above in my previous reply. For the reason
you have stated it can't work.
If a blade\sail at the top of the turbine is producing a foce perpendicular
(as it must) to the apparent wind then one at the bottom will produce a
similar force in the opposite direction. The sum of the two will be zero,
so there is nothing for the keel to work with.
However, the 'lift/drag" analysis is a simple and effective method to
detirmine the available energy, and what it must overcome. A modern glider
wing can achieve better than 40/1 lift to drag. Although the best turbines
will not achieve that level of efficiency there is still a lot of spare
energy there, no doubt.
It would require one very inefficient hull, transmision and propellor to
waste the available energy at a ratio of even 25/1.
Vince


I still think my original argument prevents any boat from making
progress directly into the wind. It's a simple change of reference
frame argument. Have you guys done collision problems for homework?
You frequently observe the collision in the "lab frame", but realize
it's more convenient to do calculations in the "center of mass" frame.
So you transform to the cm frame, do calculations there, and then
transform those results back to the lab frame.
In this case, an observer O standing on the ground is our
"lab frame". He feels a wind, and transforms to a frame in
which there's no wind (since the wind is moving with constant
velocity, that's just another inertial frame).

Stationary reference frame (w.r.t. ground) for observer O
|
| <------ wind speed, -w
|
| ---> boat speed, v
|
| water speed = 0
|
---+------------------------------------------
|
Observer O sees an unpowered boat floating in still water,
headed directly into a wind.


Reference frame moving at speed -w for observer O'
<------ reference frame speed, -w
|
| observed wind speed = 0
|
| ---------> boat speed, w+v
|
| ------> water speed, w
|
---+------------------------------------------
|
Now, Observer O' sees no wind, and an unpowered boat floating
in moving water. But the boat is moving faster than the
water it's floating in. That's clearly not possible.
Therefore, the same situation as seen by the original
oberver O is also not possible.
--
John Forkosh ( mailto: j...@f.com where j=john and f=forkosh )



It can't work because the wind pushes any structure backwards when it's not
attached to anything such as a boat in water. You and others make the BIG
mistake of considering the windmill on a boat the same as a windmill on land
where the land pushes back with the same or greater force as the wind pushed
against it. So when it comes to a boat you dismiss these backwards forces
(because you dismiss them on land with no ill consequence) when you've GOT
to account for them because the boat isn't attached to anything. Duh!

As far as it not working if you don't have any wind, what about apparent
wind. If your silly windmill on a boat would work all one would have to do
to get the thing up and running in a flat calm would be to row in any
direction until the wind propeller experienced an apparent wind from
directly ahead. Then all this magic energy from the wind would be enough for
the wind propeller to drive the water propeller and make the boat go even
faster so the apparent wind from directly ahead would be even more strong
thus even more water propeller power would be produced until you'd have to
have some sort of brake to keep the thing from going faster and faster even
though it was flat calm. This illustrates how stupid the assumption is that
one can use a wind propeller to drive a boat directly into the wind. It
simply cannot be done. Sorry! It's pie-in-the-ski and it's lame and anybody
who claims to have done it is a liar.

Wilbur Hubbard

It is indeed inconceivable provided one is of sound mind and has a basic
understanding of the laws of physics. Substitute the tree for a Danforth
anchor. No matter how hard you try the boat will never be able to make it's
way towards the anchor. The best it will ever be able to do is take about
half the force off the anchor line. If you had a big fish scale on the rode
and attached to the boat if it read 50 pounds at rest and the wind was
blowing at 20 knots you might be able to get it to read 25 pounds with the
most efficient system possible but the boat would never move towards the
anchor because to do so one would need to somehow derive and use, without
mechanical loss, slightly more than the fifty pounds of force embodied in
the wind. The disc of your propeller, no matter how large, is driven
backwards with more force than it can create out of the rotational force.
The faster it spins the more backwards force there is.

Wilbur Hubbard

Sorry but it is definitely NOT feasible. If it were feasible don't you think
there would be energy producing systems using this concept? How about
automobiles on a freeway. You could drive them onto the freeway with a small
petrol engine. There they could hook to a steam catapault such as on the
deck of an aircraft carrier. The steam catapault would launch them up to
70mph and this would spin up their air propeller as if there were a 70mph
wind. Then the automobile could then travel across a continent using all
this magic energy you crazies claim exists in this windmill system. Don't
you think if all this free, magic energy were available it would be in use
today.

Wilbur Hubbard

If there was a 'free' force pushing back on the windmill (like a keel
or the weight on the other end of the pulley on a cable car) then I can
fully see how it could climb direct into wind. But as described *if* it
was a lossless system I am buggered if I can see how it goes forward
using the force pushing against it to push back.

Wrong. They cannot be constructed. Have not been constructed and
never will be constructed.

If they were they would be a system that produces something for
nothing. Just another version of the perpetual motion machine that
also has never been constructed.

Think, man, think. If a sailboat could use the wind to go directly
into the wind then a land-based vehicle could do the same.

Who would need internal combustion engines? Just jump into your
car with the windmill on top. Face it into the five mph wind and away
you go.

Pretty soon the car would be making its own wind (apparent wind)
of greater than five miles per hour so it would go even faster. Pretty
soon, it would be going sixty miles an hour. As long as it was going
sixty miles an hour, it would go any direction at sixty miles an hour
all day long and because it was making more energy at sixty miles an
hour than at thirty miles an hour one would have to stay on the brakes
to keep it from going 120 miles per hour.

So stupid a belief. The only reason land based windmills produce electricity
is because they are fixed to the earth. Whatever windforce that pushes
upon them the earth pushes back with equal force. If the earth were not
there holding the windmill in place the windmill would blow backwards
at the same speed as the wind and fail to produce energy.

Untether it from the earth and install gears and motors to move it forward
into the wind and the loss of energy involved in the mechanical systems
as heat and friction will never allow it to even stay in place let alone move
forward directly into the wind. (zero degrees)

You don't get something for nothing. If and when you do, the known
laws of physics will have to be rewritten.

Get the shit out of your brain.

Captain Neal

From Toad of Toad Hall

Agree.

There are more photo's of the Loch Ness Monster than working upwind
windmill boats and Jacque Cousteu's windmill ship web site
specifically says the wind has to be in the right direction.

I don't think the paucity of them proves they don't work but it's far
from proof they do work.
--

I think a device that takes oncoming wind and pushes back with enough
power to overcome the drag of the windmill and still output a bit more
power 'free' would have a very good economic case.

If it worked you could put a windmill on top of cars and convert the
oncoming airflow into extra 'free' power increasing both fuel economy
and performance.

Yet all the windmills I've ever seen seem to create a lot of drag and
little power - certainly not enough to hold themselves upright IYSWIM.

A worked formula is required to settle this one IMHO.
--
I don't think we should limit the means of propulsion, no, but it
doesn't change anything. But thinking of a fan-propelled machine does
serve to demonstrate the impossibility of the idea. If you're not
generating enough power to drive it along by one 100% efficient
method, then no amount of 100% efficient mucking about converting to
driven wheels or whatever will give you any more oomph.

-- From Toad

Not really. Looks very much like a few crackpots to me and on the
threads there's general disagreement. There's more people claiming to
see the loch ness monster than claim to have built a wind driven
craft.

Add to that the fact that wind doesn't travel in one specific
direction. So you could be in your windmill boat driving 'upwind' when
in fact 20 per cent of the wind that reaches you isn't on the nose at
all.

Also I think everyone agrees that if this works it doesn't work very
well. Otherwise every vehicle that moves would have a propellor on it
giving added efficiency from the wind. _So_ there would seem to be
lots of scope for confusion if you were driving one of these things.
In a craft clawing forwards at 0.5kts with a bit of tide, localised
windshifts and eddy currents etc.

Which isn't to say that it's not possible, merely that in this case
seeing isn't believeing.

--- From Adam


I think what you are saying is that the vessel is powered by the very wind it is overcoming? The wind blows towards you which turns a fan which powers the motor to propell the vessel in to the wind. If this is the case then you are nuts! The wind is pushing you back and 90% of that energy can be converted to the motor pushing against the wind which is itself only 90% efficient (81% in total) so you are now only being blown back 19% of what you would have been but no net forward motion.


Autogyro boat zealots, for that is what windmill powered boat fans are
called, find themselves in that gray area between theoretical possibility and
practical impossibility.

The conclusion is that the windmill scheme is not feasible for moving a
trawler against the wind and is not significantly better than traditional methods
of boat propulsion off the wind. We will have to look elsewhere for an energy
saving means of mechanical propulsion. Perhaps wait until cold fusion comes on
line.

Larry Z

My approach shows that no boat can sail straight to windward. As we all know, we tack upwind. The forward motion is the result of the force of the wind in the sails and the lateral resistance of the boat in the water. There are parasitical losses in friction wind and wave resistance and heat. I think the "Law of Conservation of Energy" applies because for that model to go upwind, energy would have to be created out of nothing. I am convinced that is not what happens there. I may be missing something when calculating the force vectors, but can't see what. If this works, it will revolutionize sailing. However, seeing is believing. All the designs I've seen that claim to go straight to windward don't work.
__________________
Gonzo

For a turbine to produce more energy than the drag it creates, it would be necessary for it to create energy. An ideal turbine, that is 100% efficient, would produce an equal and opposite reaction to the power produced. This means that the forward force and the opposite reaction cancel out. In a real turbine and propeller system, the added losses produce a net force directly downwind. Apparent wind is the result of movement, that is expenditure of energy not a gain.
__________________
Gonzo

 

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