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  1. #85
    Quote Originally Posted by mikerb View Post
    ....I do not find it difficult. The rig creates lift...that is what it is designed to do.


    Sorry, I missed this comment earlier.


    It's important here to understand the basic use of the term 'lift' in sailing.

    Unfortunately, it's a term inherited from aircraft where a horizontal wing actually creates vertical lift as air flows over it.

    In sailing we still use the term 'lift, but our 'wings' are vertical sails and in fact the lift is almost all sideways and with a forward component but not upwards.

    So while the rig is upright with the mast fairly vertical, the rig is not lifting the board out of the water.

    A fin also creates lift, again from a vertical foil. the lift is again sideways with a forward component. Curiously, because of the railing effect on the hull, a long fin just create some element of vertical lift on the hull. (However, if the rig did the same thing then that vertical lift component would be downwards.)
    Now back in the UK.

  2. #86
    I was arguing that our sails are no longer angled to windward, but that when we rake the mast aft you could argue there is then some vertical lift from the rig as well as the main sideways and forward forces.

    We can argue all day about fin lift, but it’s not just fin area which counteracts the sideways load from the rig.
    The vertical lift from some fins comes from the water wanting to reject the fin - a force a bit like squeezing a fruit pip between two fingers, causing it to squirt across the room.

    None of these things tell us much about boom height!
    Now back in the UK.

  3. #87
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    Quote Originally Posted by basher View Post
    Sorry, I missed this comment earlier.


    It's important here to understand the basic use of the term 'lift' in sailing.

    Unfortunately, it's a term inherited from aircraft where a horizontal wing actually creates vertical lift as air flows over it.

    In sailing we still use the term 'lift, but our 'wings' are vertical sails and in fact the lift is almost all sideways and with a forward component but not upwards.

    So while the rig is upright with the mast fairly vertical, the rig is not lifting the board out of the water.

    A fin also creates lift, again from a vertical foil. the lift is again sideways with a forward component. Curiously, because of the railing effect on the hull, a long fin just create some element of vertical lift on the hull. (However, if the rig did the same thing then that vertical lift component would be downwards.)
    Yes I know.....I assumed others interested in this topic would also know what lift in this context means.

  4. #88
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    Quote Originally Posted by Wing 11 View Post
    Just one note,fin not create forward component,fin create sideways force plus backward component(drag).

    In definition Lift is component of force prependicular on oncoming flow direction(air,water..)
    Drag is parallel with oncoming flow direction..

    Resultant force is vector sum of lift+drag...

    Lift force dont mean strickly that something must lifitng up upwards,like most people think, just because it's colled "lift".

    So if sail stay 100% prependicular to water ,there is no component of force that create lifting board,only sideforce
    In reallity sail is lean slightly windward so there is small amount of lifting force..

    Attachment 15770
    yes correct....the keeling action of both balanced by the fact we stand close to the windward rail. No downward forces in your diagram!

  5. #89
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    Quote Originally Posted by basher View Post
    I was arguing that our sails are no longer angled to windward, but that when we rake the mast aft you could argue there is then some vertical lift from the rig as well as the main sideways and forward forces.

    We can argue all day about fin lift, but it’s not just fin area which counteracts the sideways load from the rig.
    The vertical lift from some fins comes from the water wanting to reject the fin - a force a bit like squeezing a fruit pip between two fingers, causing it to squirt across the room.

    None of these things tell us much about boom height!
    Oh but it does...it confirms the primary force that trims the board fore and aft is the riders feet and if you raise the boom you take weight off the front foot and hence off the nose. Lower the boom and you load your front foot helping to pin the nose. Use a more powerful sail and the rider has to be able to exert greater pressure with the feet, hence on slalom boards it is normal to use much bigger and more powerful sails to ensure control ( and usually bigger, stronger and heavier riders!), than would be the case on boards with longer planning flats, less aggressive rail shapes and less powerful fins.

  6. #90
    Other views are available – and maybe that's the great thing about windsurfing.

    You might also try sailing/yachting forums, where they have the same heated pseudo-scientific debates about what does what and how.


    It's one way we spend our evenings.


    Planing is spelt with two 'n's, not three.

    You can google that, and you can google 'wind power in sailing'.
    Now back in the UK.

  7. #91
    Senior Member lostboy's Avatar
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    Quote Originally Posted by Wing 11 View Post
    You probably mean on this:
    Attachment 15765
    The distance between the dotted line and the centre of gravity is the pitching lever the driving force is acting through.
    The upwards angle and the low position of the sail help reducing the pitching lever pushing the bow down
    .
    carrying a lot of mainsail downwind in particular tends to push the bow down.


    Why do you think that mfp exist only downwind?
    it is true when sail downwind is maximum but whenever board is going, sail drive/thrust force componente exist even when going upwind, so .....

    Anyway in today windsurfing,we always sail with apparent wind from front,so sail always feel wind more or less like "upwind" figurativley speaking..

    Question for you:

    1)Does high boom has less pitching lever (I mean lever on my picture,not lever about boom like pivot etc..)?
    2)Does high boom has more upward angle drive force?

    If someone can confirm these two question then we have final conclusion.

    video of too much pitching moment in downwind sailing:
    That is brilliant - not the video, but your choice to use on the basis that it reinforces your argument. Explain to me how that was generating a downward force until forced off the plan by stuffing the nose into the back of the previous wave (at which point the rotation around the centre is relevant because of the braking force on the nose). Then apply that to a planing windsurf board and MFP.

    I've been away for a few days and you're still struggling with this aren't you, bless.

    Once again - how does a sail designed to pull forward on a rig that is predominantly sailed canted backward and to windward generate any downward pressure? I''ll even give you another clue as to the myth that is MFP if you like - stop looking at the rig and think about the responses of a planing hull as it accelerates and decelerates.
    Got an opinion? Great. Guess what, so's everyone else!

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