The Wind Powered Sail-less Boat

Discussion in 'Boat Design' started by DuncanRox, Oct 20, 2008.

  1. Tcubed
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    Tcubed Boat Designer

    There's no point arguing with Mathematics, so i'm anxiously waiting for the mathematical analysis backing your flowery language.

    The thing with saying wind powered or water powered is actually a bit misleading- it's just a way of trying to help the mind over some counter intuitive parts of the problem.

    The ice boat is moving due to the balance of forces between sails and skates, so it is no more wind powered than it is ice powered. It needs both and relative movement between both to work. Another similar example is a glider ; is gravity or wind powering it? Again both are needed. With a sailboat too, is it sail or keel powered, again it is the resultant vector forces of the two combined which create forward acceleration until reaching speeds at which (due to increasing resistance and drag) the vectors balance each other out and no further acceleration is realised i.e. constant speed. Where it not for the buildup of resistance a sailboat would accelerate indefinitely.

    The images are (my new best guess) rot starting in wood and spores.
  2. philSweet
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    philSweet Senior Member


    Regarding turban powered boats. I'd just like to mention that you can extract more power from a moving flow using a turban at the surface than you can using a turbine in free flow (far from surface). The latter runs afowl of the Bentz Limit introduced by Guillermo earlier in this thread. The former does not! The Bentz limit defines the best you can do in a WORST CASE senario. A futher pleasant confusion?
  3. Boston

    Boston Previous Member

    MR Sweet
    it makes sense
    a submarine encounters the most resistance at something like one half its diameter bellow the surface
    ( something like, its been about thirty years since I was in a fluid dynamics class )
    so its more efficient to travel either breaking water or at depth
    and so the area of greatest drag for any submerged object is a function of its depth
    basic physics 101 again
  4. Boston

    Boston Previous Member

    Mr T

    and so the fundamental error in theory that is perpetual motion

    in any environment frictionless or not there is a fixed amount of available
    energy and so the ability to accelerate indefinitely is never a possibility

    no system is 100% efficient and so it is not possible to even reach the equivalent of actual wind speed on a dead down wind course let alone exceed it in a wind powered craft

    I just think the burden of proof is on the true believers
    Im the skeptic here
    so Ill wait this thing out and see if any one can explain the rubber band fan

    but I will throw a believer a bone and say
    the drag of the wheels
    the air resistance of the prop and all the friction in between
    must be exceeded by the alteration in air pressure required to move the toy forward

    four relatively simple components of the magic equation
  5. Guest625101138

    Guest625101138 Previous Member

    This is the first time you have demonstrated any propensity to actually think about the problem rather than offering drivel.

    There is a huge air propeller that would move almost at the speed of the wind if it was not turning. This would also move the boat through the water close to windspeed. This is easy to understand. The boat moves a little slower than the wind but is moving almost at wind speed through the water. So we could be 90% of the way there without any clever bits.

    We are simply adding a small turbine that extracts a little extra power from the water to advance the prop forward through the airstream. The propeller offers the advantage over a sail here because the force on the sail drops to zero when boatspeed matches the airspeed. The propeller can continue to provide thrust while moving forward through the air - nothing new there. That is what propellers do.

    The challenge is to add power to the propeller so it will spin forward to maintain thrust in the airstream.

    Because the air is already moving relative to water the speed through the water is faster than the speed through the air. This means the force required to generate the required power from the turbine is considerably less than the thrust from the propeller. This extra thrust is required to keep the boat going.

    In simple terms that you might comprehend:
    For the air propeller:
    Prop Power = BIG FORCE x small velocity
    For the water turbine:
    Turbine Power = little force x BIG VELOCITY

    The pressure difference to create this propeller force is not much because we are talking about a huge propeller. In the original example I gave for a single person boat I needed an 8m diameter propeller to generate the required force. But it is spinning quite slowly because it only has to move slightly faster than the air to achieve DDWFTTW.

    You will notice with the various land vehicle domonstrations that they have quite large propellers for the size of the vehicle. The proportion of the air propeller would be even greater for a boat that actually works.

    The key aspects are that the propeller enables us to generate large thrust force while advancing slowly through the airstream. That thrust is much greater than the force acting on a turbine in the water to spin the propeller because the turbine is advancing through the water much faster than the prop is advancing through the air.

    Rick W
  6. Boston

    Boston Previous Member

    if drivel is arguing the impossibility of perpetual motion
    then drivel it is

    and speaking of drivel

    if the propeller was not turning
    how can it almost go the speed of the wind

    just a question kids
    course a few simple questions got Socrates dead if I remember my history

    the basic problem of all over unity devices
    how to blink and derive the
    the propeller you are so attached to is in equilibrium or decelerating the instant it hit a relative wind speed proportional to its drag coefficient
    whats making anything accelerate if the system is in neutral or deceleration
    and you didnt mention anything about a slipping differential yet

    I would again refer you to the following

    speaking of dont understand
    I didnt notice any rebuttal to the my previously quoted statement

    represents a fundamental misunderstanding of the physics involved as the hole system at the time of the mythical moment can only be in equilibrium or deceleration due to the drag coefficients of both the air and water turbine being what they are relative to that of the vehicle itself

    you do seem to realize the vehicle will hit equilibrium at some point before reaching dead down wind wind speed

    and Im dying to find out what these earth shattering

    but please
    Im actually loving this thread
    we have managed to take on a slightly antagonistic approach to one another
    and we need to keep that in check
    although pleasant banter is the heart of a healthy debate
    I actually hope you come up with something to convince me
    I seek a greater understanding at all times
    ( if you are all that much interested in physics Im surprised you never asked about my patent on plasma insulation )
    and Im probably a lot more open minded than you are thinkin right about now
    so do go on

    the model you are analyzing
    Im curious
    did you make that diagram
    and if not were did you find it
    Ive got an anvil to drop on it once you guys are done playing
  7. Tcubed
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    Tcubed Boat Designer

    Mr Boston says <<I just think the burden of proof is on the true believers
    Im the skeptic here>>

    He also put forward the premise;
    <<the energy available at the transition to faster than wind speeds will no longer be significantly dependent on the variation of the mediums relative velocities to one another but as a function of the friction variations of the systems driving components relative to the mediums upon who's friction those driving mechanisms are dependent
    given that at some point in order to pass this test the relative wind velocity must pass through zero
    I believe the system will find stability if going directly down wind before crossing the light speed barrier because the amount of energy available to the system is directly proportional to the variation in either mediums relative speed to the system
    not relative to one another>>

    To which i say there is a deep flaw in reasoning, so that makes me a skeptic of this 'premise' and therefore,
    according to your own words, the onus falls on you, Boston, to demonstrate to me its truth.

    However, since you haven't been able to follow the elementary algebra in the model i would be surprised to see some meaningful supporting maths coming from you at this late a stage.

    Now on a more serious note, i would like anyone with maths abilities to join me in the following extension to the problem;
    Take the same model as Rick originally presented, but add the third dimension. I.e. include all cases of motion at different relative angles to the direction of motion of the top plate. (this would represent different headings relative to the wind)

    Again, break it into two parts, first the general formula for all angles and gear ratios, and then secondly, including an arbitrary resistance vector opposing the velocity vector of the model.

    I will work on this over the next few days myself.
  8. philSweet
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    philSweet Senior Member


    is the following what you had in mind with regards to the treatment of four forces?

    A graph with 2 lines on it -

    The first line is the resultant of forces above the water line, namely windage on the hull and force due to the fan.
    The second line is the resultant of forces below the waterline, namely hull drag and the force due to the water wheel.

    IF the first line is above the second line for all velocities 0 < v < windspeed
    AND the device travels only downwind , are we getting close?

    You seem want to rule out tacking. No flying of kites that tack back and forth, and you seem disiclined to consider the case of the yacht Hydroptere tacking back and forth in a floating drydock and towing it with a rope. Taken to its limits, this could prove very tedious conceptually. I just want to confirm that a fan is an acceptable device. Tacking involves changing control surfaces and a fan does not. Is this a reasonable distinction?
  9. kerosene
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    kerosene Senior Member

    You almost got it. I am quoting because it was almost the best worded explanation here.

    My re-treatment (co-author Masalai mutilation by me without permission :D )

    Propeller acts as a big wing/sail as in a helicopter (rotary wing). Initially the propeller is at rest (no spinning). When the wind cathces the prop (and the rest of the craft) it pushes the vehicle downwind.

    Logical so far.

    Since the turbine is in the water (we assume still water btw) it starts to spin - forcing the propeller to spin too. As the propeller blows air against the wind it causes bigger force on the boat. rest is sort of obvious.

    No with all the extra resistance of water and all that crap it might seem against gut feel. That is why the cart version is more obvious.

    Lets try again

    Propeller acts as a big wind cather and when spinning as a propller (doh). Initially the propeller is at rest (no spinning). When the wind cathces the prop (and the rest of the craft) it pushes the vehicle downwind.

    Logical so far.

    Since the wheels are on the ground they start to spin - forcing the propeller to spin too. As the propeller blows air against the wind it causes bigger force on the cart.

    Now how would it NOT work.

    Lets stop the experiment at different phases.

    1. still craft little friction on the gearbox and wheel. wind. Surely it has to start moving - if it didn't it would fight the wind with no outside force.

    2. cart starts rolling pushed by the wind. Propeller starts spinning (it has to or the wheels would skid but that wouldn't make any sense)

    3. We have a cart rolling that is blowing wind against the wind. What stops it from reaching and passing the speed of the wind? You would need brakes to do so.

    I probably failed like many before me in simplifying somewhat simple dilemma.

    And Guillermo - drop the arrogance a notch - just so happens that this time you were wrong and if I hadn't read about 1000 very valuable posts from you I might question your character :D
    1 person likes this.
  10. masalai
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    masalai masalai

    kerosene, Now I have a swollen head, but thanks, and permission granted, so long as you do not upset Guillermo.... An autogyro is a good example of a rotary wing in action...
  11. clmanges
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    clmanges Senior Member

    Someone should chisel this in stone. Big, like visible from orbit. Then pick the stone up and drop it on those youtube jerks for not having said so in the first place.
    Thank you.
  12. Tiny Turnip
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    Tiny Turnip Senior Member

    A little OT, but pursuing extraordinary wind powered machines:

    more film of Theo Jansen's work at

    I particularly like the Animaris Currens Ventosa walking clip. there is more on Youtube of course.
    It is clear that some of the machines are not wind powered, (the 'rhinoceros' for instance) and it really is difficult to get a sense of how they are actuated, though the embedded clip has a shot of Jansen apparently assembling wind powered pneumatics, I think. So, presented largely for inspiration, suspension of disbelief, and enjoyment.
    Last edited: Nov 19, 2008
  13. philSweet
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    philSweet Senior Member

    Here is a sketch of a device. It is contrived so that there is no reversal in force, torque, or rotation as it accelerates. It is shown at rest. the fan is free to pivot forward or aft.

    Attached Files:

  14. TheUnlogicalOne
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    TheUnlogicalOne Junior Member

    Just trying (and possibly failing) to be helpful here, but there is something that seems to have been forgotten. While its not required I tend to think practically and if I can see how it could be done in reality it makes things easier.

    The air prop/turbine either has to be able to swing around or reverse pitch for this to work from a stand still effectively. (at least this is my gut feeling, can't be bothered to work it out, and it would depend on gearing) If not, the wind would possibly "pull" the craft straight back. Not a bad ability but not the desired out come.

    If the prop could rotate freely to face any heading, like a windmill with a tail, then it should be fairly straight forward. Start out perpendicular to the wind and accelerate up to the required speed, then turn down wind. If you are traveling faster than the wind at an angle (which I think is agreed is possible) when you change direction the prop would swing to face forwards (where if the boat where stationary it would face back into the wind).

    I'm not entirely sure what this "required speed" would theoretically be. It is the point where, depending on gearing, more power is available from the water relative to the boat than in the air relative to the boat.(the "relative to the boat" is important I think?) Its probably below the wind speed but that would cause practical problems for the free turning prop as it would want to swivel back the wrong way and act as a brake until the boat was slowed down again.

    Unless you could change the gearing on the fly and manually control the direction/pitch of the prop the boat would not easily accelerate from a stand still to faster than the wind in a straight line. It would have to be pushed by the wind up to a certain speed, like a floating brick, where the water prop stops stalling, and if the gearing is good with low resistance it might actually reverse direction.

    I'm sure I'm out to lunch on at least a few points here, but I was bored during lunch and couldn't think of anything more productive to do.

  15. Tcubed
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    Tcubed Boat Designer

    Well at last i see someone who thinks along the same track as i.

    This to me is by far the most interesting part of the analysis of the turbine boat so far. How does the "gearing" vary with heading and V/W......???? At what angles is critical and what happens at critical angles.

    Although it is no doubt possible to make a boat with fixed pitches and gearings get to ddwfttw in a straight line, in practice i'm certain that real boats outfitted with this system would not start heading straight downwind when at a standstill. It would not be the quickest way to accelerate , basically.

    For this system to function well realistically, it needs full pitch control in both screws as well as fully variable gearing between them.

    I have been analysing the basic problem as per my previous post to precisely that end, and am trying to simplify the equations to give V in terms of G , W and alpha , As well as give G in terms of V , W and alpha.

    So far i've got G in terms of V , W and beta and am going over it again and will convert it to w.r.t. alpha soon.

    (alpha is angle between real wind vector and machine's velocity vector, beta is apparent wind angle)

    I'm glad we could get this discussion back on track and usefull, instead of wasting time trying to convince people incapable of following mathematical logic.
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