Sailors wrong for thousands of years?

Discussion in 'Sailboats' started by backyardbil, Feb 7, 2011.

  1. backyardbil
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    backyardbil Junior Member

    I found this on Youtube at http://www.youtube.com/watch?v=8Rw_qJytbG8



    With the following description:
    "For thousands of years, sailors have believed they could not use the wind to sail directly against the wind. They believed the only way to go upwind was by approaching in zig-zags (known as tacking). They didn't realise that a simple windmill could give their ships the ability to go exactly where they wanted, even if the wind was unfavourable."

    Can this really be true? I must admit the video is convincing!
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Yes it's true.. use search function and you find more..
     
  3. jehardiman
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    jehardiman Senior Member

  4. Perm Stress
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    Perm Stress Senior Member

    It is possible, but not too efficient in several departments:
    1)lets say, windmill efficiency is some 60% (wild guess)
    2) lets say, transmission/gearbox/bearings combined efficiency is some 95% (good drive train of motor driven ptopeller)
    3) lets say, propeller efficiency is some 60% (about theoretical maximum achievable for large slow turning props)

    So, we have 0.6*0.95*0.6=0.342=~34% of wind energy, received by windmill, transformed to thrust at very best. Not a lot.

    Now, we have to add aerodynamic resistance of windmill "building", above water parts of hulls.

    Further, in any sea running, heading straight against it is VERY thrust-hungry. In my personal experience: 20kn of wind and ~2m high sea, opposed by 75kW slow diesel + real 3-blade propeller on 14m, 16t extremely seaworthy sailboat; full gas, and no steerage way, no speed to talk about. So our windmill boat is in very unfavorable position, when in open waters.

    Further, practical difficulty of reefing.
    Gyroscopic effects on motion( good or bad? I do not know).

    All in all, IF it is viable, LOTS of research/PR/demonstration trips ("wrong way" round the globe?) is necessary to win this way of moving ships it's place on the worlds oceans.

    ______________________________________________

    Somewhat similar, came to mind by assocoation:
    in the 19th century, a paddle-wheel engineless ship was invented and prototype built. The paddlewheel, rotated by flow of the river, was used to turn a capstan, capstan did haul the anchor line, and so, using only the energy of river, the ship was able to move upstream. Full-size prototype did prove it. Now it remain only in the books on weird/curious/strange facts of engineering history.
     
  5. MechaNik
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    MechaNik Senior Member

    Any ideas what the super yacht version will look like???
     
  6. jehardiman
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    jehardiman Senior Member

    Yes, there really is, as perm Stress points out, a size problem.

    Here is a 3.6MW wind unit (103m dia), about the size needed for a 150m cargo ship.

    [​IMG]

    The tug off the bow probably has that half that much power installed.
     
  7. gggGuest
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    gggGuest ...

    I think it was first done in the first half of the last century...
     
  8. MechaNik
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    MechaNik Senior Member

    Any ideas about what the apparent wind situation would be when going straight into the breeze? As you go faster there is more apparent wind yet surely the drag rises proportionally too. Which one wins?
    It is much easier to imagine power generated at no/slow speed than at a cruising speed.
    Perhaps two counter rotating windmills could provide a good gyroscopic stabilising effect?

    But probably the biggest issue I see with this design is that it relies on propeller upfront pulling the vessel to maintain course keeping. I'm sorry but every vessel has to pitch and we know what happens up front when the vessel pitches.
     
  9. jehardiman
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    jehardiman Senior Member

    Is that different from what happens in the back? Think about it.
     
  10. MechaNik
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    MechaNik Senior Member

    No Hardly the same thing J. A normal prop is considerably closer to the LCG, these guys have got them way out front, unless there are designs I haven't seen.
    When was the last time you saw an ocean going boat with the prop up front as if?
     
  11. jehardiman
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    jehardiman Senior Member

    Nope, only in small vessels. For most large vessels the prop is about the same distance from the LCC-LFC couple as the forefoot. In heavy seaway you still have guard against over speeding due to prop emergance.

    FWIW, props on vessels are placed aft for efficency reasons, which is the same reason they are placed forward on aircraft. This reason for this ratio between density and viscosity for the two different fluids. Water is much more dense for it's viscosity than air. It is more efficient to recover energy (i.e. the wake fraction) out of the water wake than it is to lose efficency to wake variation (i.e. thrust deduction).
     
  12. MechaNik
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    MechaNik Senior Member

    That's why they put way out in front (way as in far, not on the hull). But I see you agree this is not the ideal place to have a propeller.
     
  13. gonzo
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    gonzo Senior Member

    They are measuring bollard pull which means it is a rigged test. They don't account for friction or wave resistance if the vessel where to move.
     
  14. backyardbil
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    backyardbil Junior Member

    Who is "they"? Do you mean in the video?
     

  15. Windmaster
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    Windmaster Senior Member

    As regards the air, I think lift and drag increase by the same amount. However, straight into the breeze, the water drag would naturally increase until a balance occurs between thrust and drag.
     
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