25 thoughts on “The Physics of Sailing – KQED QUEST”

  1. what about when a boat loses its keel (on a reef or some such), they still
    sail … forwards! albeit less efficiently and somewhat dangerously, they
    still ‘work’ from a momentum perspective. their forward moment is still
    greater than the leeway, even without a keel.

    this kind of ‘lift’ theory of aerodynamics has (in the past decade) been
    quite disputed in the field of aerodynamics anyway, as many experiments
    with airfoil (wing) designs which should not create any lift according to
    this theory – do!

    so this is not the whole story. it may play a part (maybe even a large
    part) but its not a complete explanation of whats going on.

  2. 7:47 watch the two sailboats and the motorboat, above the sailboat with the
    red sail – almost a bonus clip with a sail disaster, and a lesion by
    itself; How to NOT maneuver a boat in crowded situations. 

  3. Hey guys. Here’s a neat video explaining the physics of sailing into the
    wind (old square sail ships couldn’t do this)

  4. While it is true that the acceleration of the fluid across the curved
    surface of a wing results in a lower pressure on that surface, this is NOT
    the whole story. It is by far the influence of the increased pressure
    along the BOTTOM of the wing created by the turning of the flow stream
    encountering the surface of the wing presented by the “angle of attack” of
    the wing that generates a lot of the lift. Otherwise, a plane could NOT
    fly upside down. A flat wing generates lift with the proper angle of
    attack.

    This is an OLD explanation and is correct as far as it goes, but it is a
    vastly incomplete explanation. More modern ‘rotational flow’ theory is a
    better explanation.

    By drawing a control volume around the wing and calculating the change in
    the momentum of the flow field, the actual lift and form drag forces can be
    calculated. This of course does not calculate the frictional drag. If you
    do this for a wing where the under surface of the wing is parallel with the
    flow, you will generate a great deal LESS lift than when the wing has an
    angle of attack.

  5. “Square rigged ships only went in one basic direction – with the wind”
    PARDON?! Clearly, this statement is false. What did they do if the wind
    changed, or if they had to return home against the trade winds?
    In fact, square riggers, while not as efficient to wind as a modern sailing
    boat, could sail at a reasonably close angle to the wind.

  6. lol lucky you’re doing it somewhere warm and not somewhere freezing like
    Hamworthy (Poole, UK)

  7. “A luffing sail is not the equivalent of stall on an aircraft”, per minute
    7:40, it would be an over-trimmed sail.

  8. Hard to take this seriously when the first thing they say is completely
    wrong. Square-rigged ships can most certainly sail into the wind. It’s true
    that they can’t lie as close to the wind as a fore-and-aft rigged ship, but
    they can tack.There’s no way Magellan, Drake etc. could have made it around
    the world in ships that only sailed with the wind. Getting around Cape Horn
    from east to west is impossible if you can’t sail your ship into the wind.

  9. Hey guys, just a note about why lift happens, this guy is chatting bull.
    Bernoullis law doesnt apply in the case of a wing (or sail). For his law to
    apply, certain assumptions must be made. firstly that the fluid has zero
    viscosity, but as we can see, the fluid ‘sticks’ to the shape of the wing,
    which is a viscous effect. secondly, that it is a steady flow. which as
    said in the video, it is not. Finally, Bernoullis theorem only applies to a
    single flow, once you talk about flows above and below a wing, its moot.

    While Bernoullis can describe some of what is happening, the fundamental
    law behind lift is newtons 3rd. watch the flow as it comes off the wing,
    its at a different angle, meaning a force was imparted on the air by the
    wing, and thus vice versa

    (im an aerospace engineering student and even people in the aero business
    get this wrong (including the most of the internet), and this isnt coming
    from me, this is coming from Dr Iain Dupere at Manchester University)

  10. Your model desperately l lacks sail trim. Move your jib cars back and for
    the love of god, tighten your outhaul!

  11. How do you guys (the sailing school) get away with completely inadequate
    safety equipment for students? And then comically prodcast it to the whole
    world via youtube. You should be closed down by the US authorities. Boyancy
    aids. are not suitable life savers for offshore yacht sailing!! Inshore
    dinghysailing with supervision maybe……….

  12. I always thought that if I were to travel back thru time, this would be one
    of the most valuable bits of knowledge to have.

  13. it’s simpler to just figure out a workable route and let the sail dictate
    the angle of approach, turn away from the wind until the sail starts
    catching and let the wind push/pull you along. always look to your sail for
    information, it’ll tell you how it wants to work.

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