Porthsmouth Yardstick system - any research?

Discussion in 'Sailboats' started by Alik, Sep 22, 2016.

  1. Alik
    Joined: Jul 2003
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    Alik Senior Member

    Interested on PY system analysis, any research available, for sailing dinghies? Comparison on PY numbers vs polar plot data, for different windspeeds?

    Any links on research papers will help.
     
  2. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    The UK Portsmouth Yardstick system is entirely empirical, and deliberately so. I'm not aware of much work on polar diagrams other than Bethwaite's.
     
  3. CT249
    Joined: May 2003
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    CT249 Senior Member

    Alik, if you're trying to predict a PN, you could look up this thread.


    http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=11438&title=the-fuller-number

    "Peaky" is a dinghy sailor and naval architect who created a regression analysis to calculate draft PYs. It seems to come in fairly accurately, within its limits. It may give you an idea of comparative speeds. Whether it will work for boats as small as the one you're looking at it is another issue but it may be worth a try.
     
  4. Alik
    Joined: Jul 2003
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    Alik Senior Member

    Thanks interesting link.

    What I am trying to do, is to find corrections of PY with factors such as type of course, weight of crew, etc. Say, Laser over performs Finn at reaching, so any course with large reaching legs will be unfavorable for Finn due to its PY.

    In my opinion. PY should be only used for certain types of course, and not outside these limits. Just want to make some reverse calcs and see what we come up with. Did measurements with SpeedPuck on number of boats as well.
     
  5. CT249
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    CT249 Senior Member

    Aha! Well, gggGuest is one of the best people in the world to get information from, although I strongly suspect I know the answer!
     
  6. The Q
    Joined: Feb 2014
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    The Q Senior Member

    I plotted Several well known dinghies that I could get data for, on a graph when I was trying to get a feel for my home designed boats comparable PY.
    Using a Modified version the PHRF calculator http://www.capedory.org/phrf.html ( the download is in the middle of the big bit of text.) I eventually got a fairly good straight line on the graph.
    Notes,
    I was only interested in displacement speeds,
    I had to make alterations to change to the UK PY systems instead of the US PY system and remove things like type of propeller /engine drag and keel type as they were not relevant.

    For my case this was also plotted against the Norfolk Broads handicap, which is used where I sail and is a percentage system.
    A Star Class is normally "0" on that system and a Laser "11" that is 11% off of the finishing time.

    Part of the reason for this was some clubs on the Norfolk Broads use a straight conversion from the PY into Broads handicap making no allowance that boats like the Laser that get little chance to plane on the rivers and the shorter masted boats of any boat may well be screened from the wind by trees and buildings.

    Since I do not have access to polar plot data for any of the dinghies, this wasn't used but had it been available I would have been very interested.
     

  7. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Tough one Alik. Perhaps one of the best options is to look at the following link. though this is for the forthcoming series, data ie results should be available for the previous year along with event reports which should give some idea of windspeed etc.

    http://gjw.sailracer.org/eventsites/new.asp?eventid=203845

    Quite a number classes get revised PY numbers too so you need to check the current/prior number (if it has been moved) as well. Note that mostly these are 'big' water events due to the number of boats competing.
     
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