Centre of Lateral Resistance, Centre of Effort and lead

Discussion in 'Sailboats' started by cookie munster, Jun 26, 2017.

  1. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The "plank on edge" design that the above image somewhat resembles, was an era where lots of things were tried, including more keel drag. In hindsight we can think maybe they were looking to reduce tip eddies and vortices, but it's likely they hadn't a clue about this. You're correct in that most keel drag is relatively subtle compairtivly, but I think that (above) is one of the "freaks" developed, to find a way to beat the damned upstart colonists.

    Your experiment suggestion has been done and keel drag is just that, drag, typically tip vortice generation, but also the inclined bottom also bears on the flow as well. Take a look at any modern fin (without bulb) regardless of aspect ratio and the one thing you'll see is a fin bottom that parallels the LWL. This was "discovered" at the turn of the 19th to 20th centuries, as tank and towing tests started to make inroads to design, compaired models and empirical evidence.
     
  2. Angélique
    Joined: Feb 2009
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    Just came across what is said to be the "gold standard" for "lead" when drawing "schooners" . . . ? ?

    Atkin Boat Plans ---> Florence Oakland (design by John) ---> Article 1 ---> Photos

    1 this link is the source of the below text quote, and the two below Florence Oakland drawings.
    (from Boat Design Quarterly by Mike O'Brien, with the below quote of Paul Gartside)

    ‘‘ . . . . She is the best balanced boat I have ever sailed. I still use her lead [with a long 'e' as in 'need'] for the gold standard when drawing schooners: that is, a 10% lead (with the full rudder included in the CLR). You can control her simply by trimming the mainsheet. The rudder sometimes seems redundant. . . . . ’’

    [​IMG]

    [​IMG]

    Article: The Atkin Design Legacy 2 - (by Daniel MacNaughton 3, originally published in WoodenBoat Magazine)

    2 this link is the source of the below Florence Oakland picture. - - 3 MacNaughton Group ---> Tom ---> Daniel

    [​IMG]
     
    Last edited: Jul 28, 2017

  3. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 471, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    L. Francis Herreshoff was the one that established that a 10% lead on traditionally proportioned schooner rigs, over traditional full keel, was a good target. These generally are heavy, full figured things and not much help with modern yachts.
     
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