help me understand this Finot VPP table

Discussion in 'Sailboats' started by balazs rozgonyi, Oct 21, 2022.

  1. balazs rozgonyi
    Joined: Oct 2022
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    Location: Hungary

    balazs rozgonyi New Member


    can you guys help me understand the attached table? Its for my boat (Oceanis 411), and seems like it was created by Groupe Finot while designing the boat.

    The problem is that there are no unit of measurements, and some seems very strange to me. But maybe these are so standard, somebody can help me out.

    Its quite clear the first column is TWA in degrees. The second row is very likely AWS in knots. Then AWA in degrees again, followed by boat speed and VGM in knots. So far so good.

    Now, I understand what heel means, but I dont know what they mean by these numbers. It seems 0.0 is a flat boat. The biggest numbers here are in 20-30, which suggest degrees, but then at 6 knots of true wind, this boat definitely heels more than 5-6 degrees when tight to wind. And I was always under the impression its better to heel the boat to leeward when in light winds. Yet this table says practically flat till 10kts TWS.

    Next, leeway. Could this be meters? sideways? Cannot be miles, and anything else does not make sense.

    Flatness, this must be an artifical number.
    Reef: I do start reefing around 15 knots. But this does not specify if reefing main, genua, or both. And what could 0.64 of reef could be?

    any ideas welcome

    Attached Files:

  2. gggGuest
    Joined: Feb 2005
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    Location: UK

    gggGuest ...

    I would expect leeway to be in degrees, but I can't say for sure.
  3. Dolfiman
    Joined: Aug 2017
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    Location: France

    Dolfiman Senior Member

    That looks like a quite old VPP (90's days ?) and most probably using the Hazen's model for the sails :
    ** Flatness is a factor between 1 (no flatness) and 0,5 (sails very flat) retresenting the capacity of the sailors to reduce the camber of the sails especially when sailing close hauled >>> Sailplan lift coefficient CL = Flatness * CLo , CLo being computed by taking into account all the sails areas A involved and their proper CL function of the apparent wind angle, typically : CLo = (CLm(awa) * Am + CLj (awa) * Aj)/ (Am + Aj) m for mainsail, j for jib .
    As the drag coefficient Cd includes a main term in CL^2, the effect of Flatness < 1 is to reduce more the drag vector than the lift vector, so when sailing close hauled it is less thrust but also a lot less heeling moment, and it is a win option when the heel angle becomes too high.
    ** Reef : also a factor <1 and applied to the whole sailplan through CL >>> CL = Reef^2 * CL, and also to the height Z of the saiplan center of effort CE >>> ZCE = Reef * ZCE, meaning that Reef represent the lowering of the sails heads and Reef^2 the corresponding reduction of the sails areas assumed roughly triangular.
    Usually, the VPP first starts to reduce Flatness when it becomes more efficient for the VMG, and then involved Reef for the same concern of optimisation.
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