Inclined Keel Pin Axis

Discussion in 'Sailboats' started by Doug Lord, Jan 9, 2018.

  1. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    jorgepease and Dolfiman like this.
  2. Dolfiman
    Joined: Aug 2017
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    Location: France

    Dolfiman Senior Member

    In line with this issue of canting keel + either daggerboard or L foil, as developed for Imoca 60, here is a 2017 academic paper by Hydrocean, VPLP & Verdier ( so written after the last Vendée globe) on the theoretical advantages/drawbacks of the various combinations. Here below the abstract, the conclusions (>> why they finally evolved from CLOUT to DALI foil) and the link to the ful paper:

    Abstract : " The aim of this study was to compare the performances of two types of daggerboard: one “classical” with a straight shape, one “foil” with a L-shape, called “CLOUT”; they were appended on the same IMOCA hull. Some of the CFD simulations were performed by HydrOcean, an engineering company specialised in marine CFD, for naval architects at VPLP design and Guillaume Verdier Architecture Navale, while another CFD group was operating foil and hull resistance analysis under the direction of Leonard Imas. This specific comparison of CLOUT versus STRAIGHT daggerboard was performed by HydrOcean.
    Two sailing configurations were evaluated: upwind with 30° incident waves and downwind with 135° incident waves. The simulations showed that CLOUT daggerboard was very disadvantageous upwind, with an increase of 15% in drag and a loss of 7% in righting moment. However, it seemed interesting downwind, with a drag reduction of 9% and a gain in righting moment of 8%. Still, these advantage are to be balanced with the sensitivity of CLOUT’s dynamic behaviour to waves: the boat drifts to leeward. That study enabled to point out the advantages and drawbacks of this daggerboard concept and it gave some clues for the improvements that could be brought to foil design. "

    Conclusions :
    "Although CLOUT daggerboard seems very promising on paper because of its versatility – a vertical area, the shaft and a lifting area, the tip, bringing side force upwind and lifting one downwind – this study revealed it had some major drawbacks.
    From the calm water simulations, it seems that CLOUT could be improved by altering the daggerboard angles on the hull as well as the involved surfaces. However, the behaviour on waves totally discredits CLOUT concept of profile camber inversion between shaft and tip.
    Another daggerboard concept with no inversion was therefore developed with a different role distribution: due to an increased cant angle on hull, the shaft is responsible for the lifting force while the tip creates side force. This is the “Dali” foil concept that has been used on the 2016 Vendée Globe (cf. Figure 14, yellow). "

    The ful paper :
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