Can a boat sail upwind?

We are having so much fun in the other physics threads I thought I’d bring something else up. This is a discussion I have seen in several forums over the years and I never saw it settled. The question is:

**If I design a boat that has a windmill facing into the wind which moves a propeller in the water… could this boat sail directly into the wind? ** (Note “directly into the wind” not just upwind)

The intuitive answer is “NO”. (If your intuition is saying “yes” there’s a one in a million chance you are a genius but there’s an almost certainty that you are not understanding the problem or you are really dense. In this last case please think twice before posting).

In past discussions there seemed to be a consensus that this was not possible. And yet, there was a consensus that a car on a solid track could sail upwind if fitted with a similar windmill. I was never comfortable with this state of things but really could not find a better answer.

While I was having lunch today I was thinking about this and suddenly it hit me! It is possible! It has to be possible. It does not go against anything we know, only our intuition.

Of course our intuition is often wrong. I still remember when I did not understand that sailing directly downwind is not the most efficient point of sail. In fact, it is quite inefficient. I also remember there was a time when I did not understand how a boat could sail faster than the wind. It seemed quite impossible. And yet, now, after some thinking and learning I understand both points perfectly and my intuition tells me something different than what it did before.

So, today I have had one of those revelations and I now firmly believe it is possible to sail upwind in a boat fitted with a windmill. I m not saying it would be very fast or efficient, just that it is theoretically possible, at least under a certain range of conditions. I mean wind speed in the range that boats use for sailing. In fact, with an optimized design it may be more efficient than a “traditional” sailboat.

OK, now I want to hear arguments for and against this hypothesis. Feel free to use the railroad car with a windmill as a comparison to support your argument. But I would like to hear some solid argument pro or con. You do not need to tell us what your intuition says as we all agree on that.
As a side issue I will relate that, some years ago, some other yatch guy was intent at explaining to me at a party his theory about “free flying” sails, this is to say sails with no spars, like a kite. At the time I did not know enough and he got me thinking. Today it is obvious to me that such sails would only be of any use downwind and could never allow tacking into the wind as traditional sparred sails do.

The resistance of water against any propeller big enough to move the boat would be greater than the force of the wind against the propeller. The mechanism would never start in the first place.

If you kick-started it, it wouldn’t continue to run by itself because the energy generated by the windmill would be less than the energy dissipated by the drivetrain, heat, gearing and the water against the propeller.

In addition, the windmill is not even close to being 100% effecient. And it has to overcome not only it’s own resistance to the wind, but that of the boat as well, not to mention pushing the boat against a wind, but through the drag of the water. The faster the wind blows, the faster the propeller goes, but also the greater wind resistance of the whole gizmo.

I vote no.

I’m sorry. Please correct the first sentence above to read" The resistance of water against any propeller big enough to move the boat would be greater than the force of wind against the WINDMILL.
PS: Changing the size of the propeller, windmill, or gear ratios in the drive train will have no effect on the problem.

tcburnett, what would be your vote on the railroad car (locomotive??) with a windmill?

Here’s one method:

Drop anchor, put up your windmill, and charge up some batteries. Put down the windmill, lift anchor, and use a motor to propel the boat (powered by the batteries). Repeat as needed.

This doesn’t have to be as clunky as the above suggests. All the anchor does is increase the resistance to movement as the wind hits the windmill- you don’t want the boat to move, you want the windmill to spin. You could accomplish this by inserting some sort of rudder-like device into the water to resist the motion. To start moving, just rotate the windmill blades (kind of like a helicopter’s blades) so they don’t oppose the wind, and rotate the rudder-device and turn on the motor.

I wouldn’t be surprised if you could contrive it so that you could let the motor run continuously, as long as something kept adjusting the windmill and the rudder-thing in response to the wind.


I see you drawing me out in preparation for the kill, but I stick to my guns. A locomotive commonly pulls thousands of tons of loaded rolling stock. If you used the windmill to supply a charge to the batteries which run the electric motors…nahhhhh…Locomotives commonly run multiple thousand-horseporer diesel engines to provide compressed air for the brakes and power for the battery banks. Trains normally run multiple locomotives. A windmill won’t cut it.

A windmill MIGHT move a maglev train, but I doubt it. Same problem, resistance to air and the weight of the train, even assuning it was levitated.

I vote no on that as well.

I doubt even that would work, but in any case the problem was stated as follows:

If I design a boat that has a windmill facing into the wind which moves a propeller in the water… could this boat sail directly into the wind? (Note “directly into the wind” not just upwind).

I think the windmill vessel can sail directly upwind. No problem. (That makes me dense or a genius … hmm…) There were sailing vessels designed at some point in history (wish I could remember) - they didn’t use canvas, they used cylindrical spinny things which work on a slightly different principle from windmills but to the same mechanical effect. The cylindrical spinny things stand on the deck like big fat smokestacks. For some reason they spin, clockwise or counter-, when the wind hits them. I can’t promise it, but I’m pretty sure that these vessels could sail directly upwind.

Let’s cheat a little a bit and consider a vessel beating into the wind. It’s obviously not directly into the wind (which is why this is cheating). Okay, now let’s say that instead of the whole vessel tacking, just the masts do. I can’t imagine the mechanics either, but let’s say that you point the boat directly into the wind, and a sail at an angle to the wind results in sideways force on the mast. The mast slides sideways on some freaky generator-rail which runs perpendicular to the length of the vessel. This turns a propeller. You’re using exactly the same principle behind tacking, but instead of the whole ship doing it, a couple of masts are dancing back and forth.

No good engineering point to it, but I think it illustrates the point - there is nothing magical about sailing directly into the wind that makes it impossible to do. The reason vessels have to sail at an angle into the wind is that there’s no (non-windmill way) to rotate motion 180 degrees. So instead we translate motion less than 180 degrees by using the keel. The windmill probably wouldn’t be very efficient for wind resistance reasons, though.

I’ll see if I can find a link but a distinctly remember this being part of a Popular Mechanics blurb a while back. The boat was rigged with sails turning a vertical shaft rather than a horizontal shaft like you’re normal windmill. Take a paper towel roll and cut into two u shaped halves. Now glue back together so that when you look at it from the end it is in an ‘S’ shape. Now mount it vertically with the shaft at the middle of the ‘S’ then power is transferred to a horizontal drive shaft and propeller in the bottom.

I’ll see if I can dig up a link.

I think arjuna has the right idea. There is nothing about the principle of a windmill which requires that it have lots of wind resistance. Let’s say the deck and windmill are both very aerodynamic, so the boat doesn’t get pushed backwards by the wind. So you have an energy storage mechanism (arjuna used a battery, I think a flywheel or spring would do) - what happens when you fold the blades and let the energy storage thang do it’s job? Forward motion, directly into the wind.

I don’t think folding the blades is counter the OP’s premise, but neither do I think it is necessary. There is no reason you’d have to go through a “flywheel middleman”. That’s why mechanical devices are so great, the allow you to change the direction of forces.

Boris B beat to the punch.
For a working model check out All About Rotary Sailing. Go back to the main page for a photo. Because this model is stationary it works best directly against the wind. It also mentions the dabate on usenet groups about this subject.

Sailor stated the problem thus:


The windmill (I am aware of vertical-shaft rotating sails) is the prime mover of the propeller. Nothing about energy-storing devices or exotic drivetrains was allowed. He asked if the boat…as described…would make headway directly into the wind that was powering it.

From sneaking in through a Google cache on a piece about Windmills that mentions Anton Flettner’s rotor ship based on the Magnus effect.

“S-Rotor. When mounted with a vertical shaft, the S-rotor type of wheel (see illustration) for a windmill has the advantage that it is not necessary to swing the unit about the vertical axis to place the working area into the wind. Although the torque, or tendency to turn about the shaft, varies from a minimum of one-third maximum to the maximum during a half revolution of the wheel, on the average, the same power will be developed independently of the direction of the wind. If a smooth circular cylinder is rotated in a wind, a force on the cylinder results in a direction perpendicular to the direction of the wind. This phenomenon has been named the Magnus effect, after the German physicist who published a treatise on the subject in 1852. Between 1920 and 1930, Anton Flettner used rotating cylinders (Flettner rotors), driven by S-rotors, to take the place of blades on windmills, and for propulsion of a ship which made a round trip from Europe to America.”

You aren’t breaking any laws of nature by redirecting energy. If you toss a ball at a wall, and it changes direction, it’s because the wall and the earth changed direction, too. Just in imperceptible amounts, due to their mass.

You are making the wind transfer energy to the water instead of the boat. The water will pile up behind and the boat will “fall” into the low area in front.

Another angle is to use a mathematical model.
Since you know you can go against the wind by tacking left and then right, it is just a matter of getting the changes in direction to be in smaller and smaller increments until they converge. Of course, that’s theory. How you would reach the quick changes required without ripping your sails is another matter.

I am glad to see this has got some people interested. Some clarifications though: The “store energy while anchored and then move” solutions are not acceptable as they are obviously possible. So Arjuna34, your solution is not what we are looking for.

The “windmill” can be of any type, be it horizontal or vertical axis as that does not change the nature of the problem.

tcburnett, when I said rail car, I just meant something, anything, on wheels, as opposed to something floating. I am not thinking of a real railroad car. Most people tend to agree it is possible to move a vehicle directly upwind using the force of the wind if the vehicle is on solid ground but not if it is in the water. That is why I was asking. But when you say even the energy storing solution would not work I think you need to think again. I think that is trivial. You could store energy for a week before sailing (motoring) for an hour. That is not what we are asking though.

Some loose thoughts:

A boat can already sail upwind by tacking. The lift provided by the keel prevents the boat from sliding downwind (making leeway). In fact, it is the lift created by the keel that takes the boat upwind (although at an angle). A boat could tack infinitely short tacks and sail upwind

An airplane wing provides lift but it has to advance in the air at a certain speed or it stalls… when I want my air vehicle to move slower through the air I fit it with rotary wings… they cover more distance through the air in the same time…

Imagine a boat with two hulls, two sails etc… just two boats united by a telescopic arm with a platform in the center where I sit. Each boat sails to windward on opposite tack. I am moving directly into the wind while each hull and keel are moving at an angle… I just need each keel moving symetrically with respect to the wind… when one goes left, the other goes right and viceversa… (note i am assuming all the lift is provided by the keel and none by the hull, which in boats like mine is close to the truth)

What the sails do is provide the energy to move the keel through the water so the keel can produce the lift to go to windward.

But we do not need two boats… just two keels moving symetrically to each other left and right… heck instead of meeting at the center and heading out again, if one was under the other they could cross… do you see where I am going? I am describing a propeller! The blades create lift in the same way a keel creates lift. While one blade goes one way the opposite blade goes back to where it started.

In this example fixed wing is to keel what rotary wing is to propeller.

funneefarmer those links were extremely interesting. Of course they provide the answer to the question: not only is it possible, it has been done! I am just a bit disappointed that what I thought I discovered today has been known for some time… Oh well… At least I can think I came to the conclusion myself, not after i was proven wrong.

Also I learnt the concept is called rotary sailing which I did not know. This model looks quite primitive and the blades can be improved. And it already works!

Very interesting but I did not expect this thread to be settled so fast. Someone has done the impossible (sailing into the wind) and it’s on the Net for all to see. Is this wonderful or what?

Ahhhh…I see that it is a semantics problem. I suppose you could have phrased the question differently but I am nitpicking. I followed the links given and did not see a propeller in the water under any of these windmills. Might you direct me to a mechanical drawing of such a craft? Or even a description of a practical boat which will propel itself forward directly into the wind using a windmill (any airfoil is fine) and a submerged propeller.

And yes, you COULD generate power for a week and then propel a boat for an hour but that is a bit impractical, no? I thought you were asking for a practical rather than a theoretical solution.

tcburnett, I am not sure what you mean saying I could have phrased it differently. I think it is quite clear and i cannot see any ambiguity. Can you explain?

As for not seeing the props in the water… well, yes… they are under water. On this page (originally cited by funeefarmer) you can see the mechanical diagram of the one in the photo I linked to above.

Following links I saw one of these boats was built in the 30s… so this is nothing new.

This page has a gadget that demonstrates the feasability of saling directly upwind. This is a toy I might attempt to build myself.

Basically it is a long pole with a float in the middle. One end is weighted with a water screw propeller and, in absence of wind, hangs vertically down. At the other end an air windmill (or propellor if you want to call it that). In absence of wind the pole is vertical but when the wind blows, it tilts the air blades to leeward and they start turning the underwater screw so the contraption moves to windward. It could not be simpler! No moving parts! I love this gadget! I want one!

If you built a boat with the windmill at the stern (causing drag) and the propeller at the bow (pulling, rather than pushing) the boat would always point and sail directly into the wind. Having the windmill and propellor on horizontal shafts would improve efficiency as the gadget described above always has the screws at an angle to the wind and water and this makes it less efficient and it still moves to windward!

Second try:
this is the page

I love that drawing (the one I got from your first link, on rotary sailing).

I think we’re making some headway. Yes, I did introduce those exotic mechanisms, not because I think they are necessary, but as a bridge between our “can’t sail upwind” intuitions and the nifty engineering (which I’m glad I didn’t have to do myself). Basically, my thesis was, if you can do it with a battery, you can do it without one.