VPP polar diagrams

Discussion in 'Sailboats' started by Eric Sponberg, Dec 16, 2007.

  1. jehardiman
    Joined: Aug 2004
    Posts: 3,066
    Likes: 570, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member


    As the others have already said, yes, you can use the "radar" plot graph option, but there are some limitations. Right now in the office we use excel to polar plot current data over time to generate a rosette and then superimpose a fixed grid, heading dependent system limits, and real-time data over the top of that. It is on the fly scalable, and as Mal and ggg pointed out you ether have to use constant angles or fiddle with it.

    Pelle alluded to scripts, but my guess some are just coordinate conversions like Gramp's example, as we do it directly from polar data without any need for scripting (though we use scripting to read data files into the spreadsheet). If you absolutely have to have some exact angle, it would most likey be better to do the polar to x-y conversion.

    If you want, I can extract the mechanics of it and e-mail you.

    PS: Didn't notice at first how old this thread was, happend while I was offline for Xmas travel. Anyway, the offer still stands if you still need it.
    Last edited: Feb 10, 2009
  2. Eric Sponberg
    Joined: Dec 2001
    Posts: 2,010
    Likes: 215, Points: 73, Legacy Rep: 2917
    Location: On board Corroboree

    Eric Sponberg Senior Member

    Hi JE

    Yes, I would like to see what you have, thank you. I tried Gramps example in post #6, and it works fine, although the ends of the concentric rings on the grid have a whoopie in them--not perfectly circular at the ends. I can make exact angles for the spokes of the grid with the correct coordinates, so that's not a problem. I'd like to see the boat speed rings displayed a little more accurately at the ends. Please email me through PM or through my website.

    Thanks again,

  3. Massimo De Luca
    Joined: Apr 2008
    Posts: 3
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Palermo

    Massimo De Luca New Member

  4. wvw
    Joined: Feb 2009
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: london

    wvw Junior Member

    Would it be possible to come to a mathematical formulla from this so that I could give in the wind angle and wind speed to calculate what boat speed could be expected ? Say if I wanted to build some program like virtual schipper... or to check my sailtrim while sailing competition...
  5. Eric Sponberg
    Joined: Dec 2001
    Posts: 2,010
    Likes: 215, Points: 73, Legacy Rep: 2917
    Location: On board Corroboree

    Eric Sponberg Senior Member

    A simple formula is not possible. It takes many formulas to be solved simultaneously, and that is why we have VPPs.

  6. farjoe
    Joined: Oct 2003
    Posts: 163
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: med

    farjoe Senior Member


    interesting website which I still have to test.

    I use Firefox to browse. Your website only takes 50% of my screen but is not scalable to fill the page. the text is unnecessarily small but readable. In my opinion a lot of screen space is going to waste.

  7. Windvang
    Joined: Jan 2006
    Posts: 180
    Likes: 7, Points: 18, Legacy Rep: 65
    Location: Rotterdam,The Netherlands

    Windvang Yacht Designer

  8. tspeer
    Joined: Feb 2002
    Posts: 2,319
    Likes: 294, Points: 83, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Yes, but it's a bit of a pain in the rear end. You have to plot the polar grid yourself.

    1. Create a series of X,Y values to plot for the grid by x=Vb*sin(gamma*pi()/180), y=Vb*cos(gamma*pi()/180) for gamma=1 to 360. Constant Vb for the rings, constant gamma for the radial lines. You can plot all the rings and radial lines as one series by putting a blank line between the data for each ring or line - that will avoid Excel plotting the transition from one to the next.

    2. Transform the polar data into Vmg and cross-wind components using the same relationships above.

    3. Plot the grid data and the polar data as separate series on a scatter plot (with the plot's gridlines turned off). I usually locate the plot in a sheet of its own.

    4. Size the scatter plot so the rings are circular. One way I've done this is to put a square drawing object on top of the plot (go to Format/Size and lock the aspect ratio). Format the scales to manual values so they won't change. Then size the square to match the plot in one direction, then size the plot to match the square in the other dimension. Delete the square.

    Crude, I know. But it's the only way I know to get a true polar plot in Excel.
  9. Eric Sponberg
    Joined: Dec 2001
    Posts: 2,010
    Likes: 215, Points: 73, Legacy Rep: 2917
    Location: On board Corroboree

    Eric Sponberg Senior Member

    Thanks Tom,

    That is essentially what post #6 was about. I have tried that and it works. It is easy to manipulate the plot so that it looks right.

  10. Massimo De Luca
    Joined: Apr 2008
    Posts: 3
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Palermo

    Massimo De Luca New Member

    Hey Ciao

    Don't ask me...i mean i didn't create the website ...i just founded and forward all of you, I usually open with internet explorer and i notice the same...but we must take care first of all of the results


  11. cloewe
    Joined: Jun 2009
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Chile

    cloewe New Member

    gnuplot and polar charts

    I am new to the forum, so first of all Hello to all!

    I recently succeded with gnuplot after fighting a little bit with the data of the IMS cetificate. Still, I'd like to have a pick at DuncanG set, it looks quite good to see if I can get the code even better..

    I am rather new into gnuplot also, but I'll share mine if someone is interested.

    Do you know any free software that can make the polar chart of a yatch with some imput data?

    Great forum, congrats.

    Attached Files:

    • pst.jpeg
      File size:
      164.8 KB
  12. arne470

    arne470 Previous Member

    Hi guys,

    Does anybody know where I can get a polar diagram of the olym. 470? Or how I can make such a diagram?

    Best wishes,
  13. SuperPiper
    Joined: Jan 2003
    Posts: 372
    Likes: 6, Points: 18, Legacy Rep: 58
    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .

    Unlike DuncanG's plot in post #9, Cloewe's polars in post #26 don't achieve the optimum VMG. The boat speed curves end before they top out. Is this a limitation of the boat's sheeting angle? If the headsail could be sheeted inboard or if the shroud base could be narrower, would this boat point higher and improve its VMG?
  14. DIY sailor
    Joined: May 2010
    Posts: 9
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: the Netherlands

    DIY sailor Junior Member

    Exell 2010 can make excelent polar diagrams. There is however one big issue that I have not been able to solve yet: it seems to be impossible to smooth the curve.

    I.e. if I have 15 degree intervals for the speeds straight lines will be shown connecting the data points.

    Does anybody know how to smoothen this curve?

    Any help is greatly appreciated.

  15. fastwave
    Joined: Jan 2007
    Posts: 110
    Likes: 14, Points: 18, Legacy Rep: 36
    Location: europe

    fastwave Senior Member

    Use xlXtrFun.dll to interpolate as many points as you want using a spline function. Then plot those. The curve should appear smooth. This dll library is a joy to work with and is a must.

    Search online
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.