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  #1  
Old 01-15-2004, 11:51 AM
Matchka Matchka is offline
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Why no wind-driven boat propellers?

The windmill has been around for a long time. It has been given linkage and harnessed to grinding mills for, what, centuries? How is it nobody ever mounted one on a ship to spin a propeller? So equipped, wind direction would no longer be an issue, all you would need to do is point the blades into the wind, magnify the speed of the propeller with some kind of cog-based transmission, and away you zip to wherever you wanna go.

The only explanation I can think of is the surface area of wind that you can harness is reduced from the gazillion sails on the larger ships. But with only one or two windmill masts and a fraction of the rigging you’d give up a lot of weight in return. Was the propeller so complicated that it couldn’t be invented yet? Or am I missing something that goes beyond a pretty major hull design change?
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Old 01-15-2004, 12:31 PM
Tapioca Dextrin Tapioca Dextrin is offline
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Propellors were invented after the steam engine.

Once you have steam power, there is no reason to put a windmill on a boat.
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Old 01-15-2004, 12:37 PM
scm1001 scm1001 is offline
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there have been several attempts. the only one I know one the web is mentioned in http://dc.endtas.com/modules.php?nam...article&sid=25
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Old 01-15-2004, 12:39 PM
RealityChuck RealityChuck is offline
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Newton explained it: "For every action, there is an equal and opposite reaction."

In other words, if you mount a fan pushing air toward the sail, it also will push the boat in the opposite direction (think of the propeller in an airboat -- it's facing backwards, but the boat goes forwards). The opposite push will pretty much cancel out any advantage you get from running the fan.

You could use a propeller like in an airboat, but I suspect that's less efficient that an underwater prop.
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Old 01-15-2004, 12:50 PM
Matchka Matchka is offline
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Quote:
Originally Posted by RealityChuck
Newton explained it: "For every action, there is an equal and opposite reaction."
You big silly, that only applies if the mechanism that produces the wind is mounted on the boat--If an external source of wind didn't work then sailboats would pretty much stay in the harbor. I could always lock my windmill and use it as a sail, right?
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Old 01-15-2004, 12:59 PM
AskNott AskNott is offline
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Many ocean going sailboats use windmills to generate electricity to recharge the boat's batteries. They have some drawbacks. The wind drag, unless the boat is going downwind, slows the boat a bit. They're noisy. They have to be tied down in a big blow so they won't self-destruct.

I'll leave the rest of this for somebody who knows the technical stuff. I have opinions about the workability of your idea, but nothing to back them up.
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Old 01-15-2004, 01:16 PM
RealityChuck RealityChuck is offline
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Quote:
Originally Posted by Matchka
You big silly, that only applies if the mechanism that produces the wind is mounted on the boat
Exactly. And since that is what the OP asked, it applies here.

Ultimately, any air being pushed by a boat-mounted windmill or propeller toward the sail will also cause the boat to be pushed in the opposite direction. The push would pretty much negate the extra wind being produced.

Again, look at an airboat. It's pushing the air behind it, yet it goes forward. If you put a sail behind the airboat, it just isn't going to go backwards -- the direction the wind is blowing.

In theory, you could use a big propellor on shore or on another boat to create wind to push your own boat (though distance would weaken it rapidly). But once the wind mechanism is put aboard, it isn't much use for sails.
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Old 01-15-2004, 01:23 PM
Fear Itself Fear Itself is offline
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Is this what you had in mind?

http://foxxaero.homestead.com/indrad_007.html

Also, here:

http://tennantdesign.co.nz/sailing/index.php?boat=111#

Here is some more interesting discussion of wind turbine boats and autogyro boats (note that autogyro boats do not have a linkage between the turbine and an underwater propeller, but instead use the autogyo priciple in place of a sail). They have some evidence (disputed) that such a wind turbine powered boat crossed the Atlantic in 1870.
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  #9  
Old 01-15-2004, 01:26 PM
Johnny L.A. Johnny L.A. is online now
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Quote:
Exactly. And since that is what the OP asked, it applies here.
I'm not reading it that way. When the OP says "How is it nobody ever mounted [a windmill] on a ship to spin a propeller?", I see it as a windmill that sticks up, with a mechanical linkage to turn an underwater propeller. No sails, and no prop pointing at sails.

In other words, I see a windmill that is free to turn in any direction; like the ones used to generate power. They can have "propeller" blades or vertical elliptoid blades. There is a shaft that goes from the windmill head down to a transmission which turns the shaft that turns the screw which is in the usual position under the boat.

Theoretically, I don't see why it wouldn't work. (Didn't they use the idea in Waterworld?) But there seems to be an awful lot of wasted energy in the transmissions. Why not just have a sail?
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Old 01-15-2004, 01:28 PM
Johnny L.A. Johnny L.A. is online now
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Fear Itself: That's what I had in mind.
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  #11  
Old 01-15-2004, 01:36 PM
Fear Itself Fear Itself is offline
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Quote:
Originally Posted by Johnny L.A.
Fear Itself: That's what I had in mind.
You might notice that they use a hydraulic system to transmit the energy down to the prop; much more efficient and easy to build than a mechanical transmission.
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  #12  
Old 01-15-2004, 01:39 PM
shelbo shelbo is offline
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Quote:
Originally Posted by Johnny L.A.
Why not just have a sail?
I think mainly so that, as one of the links above notes, you can sail directly into the wind.

That is a cool concept -- but sailing downwind would be interesting -- the faster you go, the less power gets to the propeller. At some point, sailing downwind you'd want to raise the prop out of the water, lock the windmill blades and use the windmill as a sail!

I wonder what kind of speed that "Revolution" is capable of . . .
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  #13  
Old 01-15-2004, 01:40 PM
TheLoadedDog TheLoadedDog is online now
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This thread really reminds me of Wile E. Coyote and ACME products. The two self-propelled road-going vehicles that come to mind are:
- bathtub on wheels with outboard motor facing into the tub.
- skateboard with mast and sail at the front, and electric fan at the back, blowing forwards.

I love that stuff.
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  #14  
Old 01-15-2004, 02:04 PM
GusNSpot GusNSpot is online now
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I wonder about an horizontal drum turbine? Did not see that idea worked over yet...........

You all heard it first right here on the SDMB !!!!!
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  #15  
Old 01-15-2004, 02:08 PM
Quint Essence Quint Essence is offline
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you can never get the same amount of power from the screw as you "harvest" from the windmill. While a system like that might be somewhat beneficial for sideways "tacking" it would not allow forward motion or even "tacking" against the wind as traditional sailboats need to be able to do.
In pretty much all cases, there is much greater efficiency with a standard sail and an experienced sailor.
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  #16  
Old 01-15-2004, 02:35 PM
Fear Itself Fear Itself is offline
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Quote:
Originally Posted by Quint Essence
While a system like that might be somewhat beneficial for sideways "tacking" it would not allow forward motion or even "tacking" against the wind as traditional sailboats need to be able to do.
Read my links again, Quint Essence; the wind-turbine driven Revelation sailboat:

Quote:
This Most Radical sailing craft utilizes a windmill geared to drive a large 6-bladed underwater propellor. Testing has provided positive results. Unlike a normal sailing craft this vessel makes its' best time sailing straight into a headwind.
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  #17  
Old 01-15-2004, 02:47 PM
bbeaty bbeaty is offline
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Quote:
Originally Posted by Matchka
How is it nobody ever mounted one on a ship to spin a propeller?
Apparently this has been used in home-built toys (in The Amateur Scientist column, if I recall.)

But it's extremely inefficient.

I know! First let's replace the windmill with a solid-blade propellor like the ones in those big wind-power generators.

Then, rather than spinning the propellor, lets strip off all but one blade, connect that blade directly to the hull, so the hull becomes the "propellor hub."

Then lets take the small underwater propellor and do the same. Strip off all but one blade and mount that blade so it sticks out of the center of the hull underwater.

And now, rather than having a spinning device, instead our "Single Blade Wind Powered Watercraft" or SPWPW can move at high speed diagonally across the water. Rather than spinning at high speed in a circle, the "blades" still move "tangentially" without ever having to spin. But after awhile you'd end up far sideways from where you'd want to go.

So lets set things up so the "blade" can flap around to the other side, reversing the sideways motion of the ship. Eventually you'd end up back where you'd started in the horizontal direction, but you'd have progressed far into the wind. (Rather than having a rotating windmill, the whole ship moves slowly back and forth, reversing direction every few minutes while making headway into the wind.)

I wonder if I could get a patent on this SPWPW machine. People wouldn't even see it as a "machine," since there are no rotating shafts or gear drives. All the impedance-matching gear mechanisms are blended into a single shape. It's almost disturbingly organic. Or like something created by an alien mind.
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  #18  
Old 01-15-2004, 03:50 PM
kniz kniz is offline
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I believe Jacque Cousteau developed and used a ship that used such a means of propelling his ship. It had what looked like a mast in the center of the ship. The mast was shaped somewhat like the wing of a plane. I have no idea how it worked and cannot find any information with a google search.
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Old 01-15-2004, 03:56 PM
Chronos Chronos is online now
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I recall seeing once a toy which would sail directly into the wind. The device had no moving parts, or rather the whole thing was one single moving part. It consisted of a long shaft with a wind propeller at one end, a water propeller at the other, and a float in between. In still air, it would float with the wind end pointing up, but a wind would tip it over and spin the whole shaft, such that the water propeller would draw it into the wind.
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Old 01-15-2004, 04:46 PM
Matchka Matchka is offline
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Quote:
Originally Posted by kniz
I believe Jacque Cousteau developed and used a ship that used such a means of propelling his ship. It had what looked like a mast in the center of the ship. The mast was shaped somewhat like the wing of a plane. I have no idea how it worked and cannot find any information with a google search.
I remember this. Wind passed over the vertical "wing" creating a sort of horizontal lift. The wing could be rotated so a breeze from the side would effectively "lift" the boat forward. Winds from the front or back could be used but the boat would lean a bit. Forgot about that one. As I recall J.C. wasn't impressed with the performance.
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Old 01-15-2004, 06:44 PM
Spectre of Pithecanthropus Spectre of Pithecanthropus is offline
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One problem I can imagine is when you want to go downwind. As the boat approaches windspeed, the relative windspeed of the boat would theoretically approach zero, though I suppose water resistance might prevent the boat reaching windspeed. This would keep the turbine going, but it would obviously be the slowest direction of travel for the boat.

But, this is just my imagination working. IANANaval architect or engineer.
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Old 01-15-2004, 09:58 PM
bbeaty bbeaty is offline
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Quote:
Originally Posted by kniz
I believe Jacque Cousteau developed and used a ship that used such a means of propelling his ship. It had what looked like a mast in the center of the ship. The mast was shaped somewhat like the wing of a plane. I have no idea how it worked and cannot find any information with a google search.
Nope, the sail was not an airfoil, instead it was a rotating cylinder. The "Alcyone" magnus-effect craft.

Search on

http://www.google.com/search?q=%2BCo...gnus+effect%22
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  #23  
Old 01-18-2004, 06:17 AM
scm1001 scm1001 is offline
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I suspect one problem with all props is that in very high wind speed they might become dangerous? At least with a sail you can take it in.
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  #24  
Old 01-18-2004, 06:28 AM
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Another problem, it seems to me, is that a windmill needs a cantilevered mast with no rigging because you need clearance for the blades. It would be significantly heavier than a conventional mast which consists of a thin pole supported by multiple cables.
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Old 01-18-2004, 09:06 AM
LSLGuy LSLGuy is offline
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Here are some ruminations on why it isn't such a hot idea and hasn't become popular yet.

Large rotating objects have nasty gyroscopic effects.

Consider the typical land-based wind power turbine: a fixed vertical tower with a rotating horizontal base plate atop the tower. A generator with a horizontal shaft is mounted on the rotating base plate. Then a blade set like an airplane propeller is mounted to the shaft with the rotating blades forming a circular disc in the vertical plane.

Rotating the base plate in azimuth to point the turbine axis into the wind generates some hefty dynamic gyro forces that the tower structure has to absorb. The good news is that although the wind changes direction continuously, it generally does so slowly.

Now put that same assembly on a boat: Rather than being absolutely stationary, the base plate is swaying and coning in 3D. Yowza! The gyro forces go off the scale.

And since the gyro forces are 90 degrees out from the masthead motion you have very bad effects on the boat's stability. As a wave makes the boat, say, pitch bow downwards, then the gyro forces will create a heel to the left, or the right, or maybe even increase the pitch-down, depending on the wind direction (ie turbine azimuth in boat-centric coordinates).

So I'd argue that a turbine like that is a loser. A drum turbine with a vertical axis might be a little better.


Now let's turn to power output. For some good learning, try www.awea.com

Here's a simplified formula for power output from a propeller-style wind turbine that I derived from one of theirs. I converted the units from metric to american and assumed typical-good values for a couple of efficiency factors.

P = R^2 * V / 115, where P is output power in horsepower & R is turbine disc radius (blade length) in feet & V is windspeed in mph.

So a turbine with 1 foot blades, i.e. 2 foot diameter, in a 10 mph wind produces 1^2 * 10 / 115 => 0.08 HP. A 10' diameter prop in a 20 mph stiff breeze produces 5^2 * 20 / 115 => 4.35 HP.

And that's HP at the turbine hub, ignoring bearing friction in the shaft, any losses in the power transmission system to the water-prop, and the coupling efficiency of the water prop to the water. If the turbine turned an electrical generator that powered an electric motor to drive the water prop, you'd be looking at about .9*.8*.8*9 = 52% efficiency for the bearings, generator, motor and bearings again. And electrical is probably the lowest-loss transmission technology available, certainly better than mechanical, probably better than hydraulic.

So for the 10' diameter turbine producing 4.35 HP, you'd have about 2.25 HP delivered into the water prop.

So much for power delivered, now how about power required?

I used to have a 27' sailboat. That's a typical family weekend sailboat for lakes, bays and near-shore ocean sailing. It's certainly not a yacht for the rich or famous, nor is it big enough to do any useful cargo hauling as a working boat.

The aux motor was an outboard that supposedly put out 8HP. At full throttle that motor was sufficient to move the boat to "hull speed", the fastest that hull shape can push thorough the water without the drag curve going all-but vertical.

If we assume the 8HP figure was the truth and was measured at the motor's prop shaft, then we can work out how much turbine we need to duplicate that awe-inspiring amount of power.

We need a turbine where R^2 * V = 1769. So a 1' blade-length will be enough if the wind is blowing at 1769 mph, i..e Mach 2.6! A 5' blade length will be enough in a 71 mph wind, i.e a baby hurricane. A 10' blade length will be enough in a 18 mph wind.

A decent modern sailboat can hit hull speed in about 12 mph of wind. That needs a turbine with a 13' radius. And just like a conventional sailboat, power & hence boatspeed will be less in less wind.

So we need at least a 13' blade length, 26' diameter wind turbine to drive our sailboat as well as conventional sails. And as others have said, the wind the turbine "feels" is the vector sum of the wind motion over the water and the boat motion over the water. So traveling downwind you'd want a much larger turbine since the faster the boat goes the slower the wind feels.

Assuming you don't want to get decapitated, you'd want that mounted on a mast at least 23 feet above deck level. That's about the same height as typical sailboat mast for that sized boat, but you also can't have any support rigging since the turbine must be free to rotate in azimuth. So it needs to be real stout compared to a conventional mast.

Last of all, 100% of the forces on that mast are applied at the very tiptop. On a typical sailboat, the sails taper and so most of the force is applied near the bottom.

So we're talking about needing a MUCH more rigid and stout mast structure to carry the extra loads due to lack or rigging multiplied by the lever arm effect from all forces being applied at the top, multiplied by the gyro issue I mentioned at the outset.

That's a tough set of problems to solve. But it might be kinda fun.
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  #26  
Old 01-18-2004, 10:13 AM
aerodave aerodave is offline
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Quote:
Originally Posted by Spectre of Pithecanthropus
One problem I can imagine is when you want to go downwind. As the boat approaches windspeed, the relative windspeed of the boat would theoretically approach zero, though I suppose water resistance might prevent the boat reaching windspeed. This would keep the turbine going, but it would obviously be the slowest direction of travel for the boat.

But, this is just my imagination working. IANANaval architect or engineer.
But how is this any different from a sailboat? If you sail directly downwind, you eventually approach zero velocity relative to the wind. Diminishing returns and all that.

So what's the difference between sails and windmills in that case?
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