Artemis Technology--Sustainable Future

Discussion in 'Boat Design' started by Doug Lord, Jan 29, 2019.

  1. Doug Lord
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    Doug Lord Flight Ready

     
  2. John Perry
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    John Perry Senior Member

  3. sharpii2
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    sharpii2 Senior Member

    Nonsense! Energy cannot be created or destroyed. There must have been at least some wind. Or they could do the same stunt on a windless bay. Just tow the cat at ten knots then cut her loose to sail the rest of the day on her apparent wind. Hey! I was born during the day, but not yesterday.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    For the record apparent wind sailing is not new. Some multiples of windspeed are new. I imagine the F 50 and maybe the NZAC 75 will set new records for top end multiples of wind speed on the water. Iceboats can do 5 times windspeed or more...
     
  5. sharpii2
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    sharpii2 Senior Member

    But that's not the claim here. The claim is that it drifted down stream at 10 mph then used the apparent wind, created by that downstream drift, to sail back upstream. With no other wind. Not even a breeze.
     
  6. philSweet
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    philSweet Senior Member

    Yes, sharpie, that's exactly what they do. They still have to tack, of course. They are tacking downwind faster than the wind. We had a wild thread on that (DDWFTTW) a few years ago..
     
  7. Angélique
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    Angélique aka Angel (only by name)

    In a response to another post I've posted my view on this thread's post #1 video, on the thread Evolvement of foiling sailboats over the last 70 years, below my post #46, and Doug's response in post #52, both as a quote transferred to here since this is the subject thread about the video...
     
    Last edited: Feb 7, 2019
  8. trip the light fandango
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    trip the light fandango Senior Member

    Going faster than the wind is about creating momentum and developing less friction and more lift, particularly foils . The apparent wind is just apparent, the profile of the sail is fine enough to not create significant disturbance. As you travel a 5knot wind is not just hitting your sails ,but ready to meet your sail as you reach it perpetually. As has been shown in wing/sail shapes with wind, the air begins to part immediately before the sail slices through, presumably water does the same. That is how I comprehend it, I'm happy to be convinced otherwise. The profile of the hull/ cabin etc above the water needs to be such that it also doesn't create much resistance, then there's overall weight to sail area.. I pickup all this stuff on forums,, ha,, thanks ...I think...ha. So with no wind it would be current, not apparent wind creating propulsion diagonally across, but some kind of swimming action with lateral fins would be able to develop speed like a whale tail most likely. pulling harder then releasing across a current would create a longitudinal/ vertical fin, swimming action, too,.. is my take. cheers
     
  9. OzFred
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    OzFred Senior Member

    … the definition of "faster than the wind".

    If only speed (a scalar quantity) is considered, then it means a boat speed with a higher value than the true wind speed. That has been possible for decades, it doesn't require a highly specialised, multi–million, dollar hydrofoil–equiped catamaran. Though it probably does require the boat to be hydroplaning if it's a monohull, but not if it's a multihull.

    Velocity, on the other hand, has two dimensions: speed and direction. Given a wind velocity of say 10kn S, then going "faster than the wind" means having a velocity in the S direction with a speed greater than 10kn. In sailing terms, it means a VMG to the leeward mark greater than the windspeed, where the leeward mark is an infinite distance away, or directly S of the boat.

    That has never been shown to be possible. There is likely a mathematical proof of its impossibility based on VMG, true wind angle, boat velocity and drag, but it's beyond my meagre mathematic skills to do more than propose its existence.

    Per Doug Lord's post, even John Perry doesn't believe the marketing spin he's been asked to spruik. In order to achieve a velocity faster than the wind, either drag must approach zero or speed some incredibly high number, while the sails are generating forward thrust at some vanishingly small angle of attack to the apparent wind.
     
  10. OzFred
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    OzFred Senior Member

    But that's not the claim. In your scenario (no wind, no current) the apparent wind is always directly on the bow. The only way to fill the sail is to push it out to one side, effectively backing it.

    In the Amazon scenario, the energy comes from having a sail in the air and a foil in the water, with a difference in the velocity of the air and water that resolves to 10kn in some direction. That's where the energy comes from, an equivalent is a 10kn breeze with no current (or 5kn of each, directly opposed, etc.).

    The fallacy is the presumption that energy can be recovered to achieve forward propulsion regardless of the velocity of the boat with respect to the wind/current velocity.
     
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  11. trip the light fandango
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    trip the light fandango Senior Member

    Yes outrunning the wind going directly downwind I don't get, but going faster than the wind, on a broad reach say as you described first has been a source of fun for ages .. So I take it you would agree with my comments on apparent wind not generating speed for the craft in itself?
     
  12. Angélique
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    Angélique aka Angel (only by name)

    It can be done by wind turbine propelled land craft, which also works on water craft, and also directly against the wind, the latter not so fast though . . .







    P.S. - DDWFTTW (Directly Downwind Faster Than The Wind) - = Blackbird
     
    Last edited: Feb 7, 2019
  13. Angélique
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    Angélique aka Angel (only by name)

  14. trip the light fandango
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    trip the light fandango Senior Member

    It the first few look like a setting for Don Quixote. The treadmill one was pretty amazing.
     
    Last edited: Feb 7, 2019

  15. OzFred
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    OzFred Senior Member

    It works on land because there is very little friction between the vehicle and the surface it's running on. It won't work on a boat because friction between the boat and water is very much greater and you'd need a paddle wheel or propeller in the water to turn the turbine, which is much less efficient.

    It won't work on a sailing boat because sails don't spin to generate their own apparent wind.

    I expect the treadmill thing only works at a specific speed, or narrow range of speeds, and doesn't work from a standing start. The propeller has to get up to speed (which it does very quickly, being so light) before the vehicle is released.
     
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