Foils and Foil-assist for Sailing Super Yachts

Discussion in 'Sailboats' started by Doug Lord, May 17, 2019 at 6:53 AM.

  1. Doug Lord
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    Doug Lord Flight Ready

    Thanks to David for this:
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Chistera.jpg Figaro 3 with Chistera foil.jpg
    I read this paper and was curious where the term "Chistera" came from relative to the foil used on the Figaro 3. Turns out a Chistera is a wicker scoop used by a jai alai player!
     
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  3. OzFred
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    OzFred Senior Member

    Some more revealing quotes:

    4.5 DISCUSSION
    The towing tank testing of the three main options for foil-assisted monohulls has been conducted for a range of upwind and downwind conditions.

    Overall, building on the experiments undertaken and hydrodynamic data gathered, it appears that, for foil-assisted monohulls, no resistance advantage over a design without foils could be achieved, thus demonstrating their inefficiency under the present test conditions and inherent limitations, namely the pure hydrodynamic efficiency of foil-assisted monohulls.

    5.3 RESISTANCE
    The results proved very consistent with the original hydrodynamic efficiency experiment in that the lowest resistance is always achieved without foils. Indeed, despite the vertical heave (only significant from Fn=0.5), the reduced displacement and wetted surface area are never sufficient to overcome the added resistance and induced drag of the foil. Notably, the configurations providing the most righting moment, namely the Dali-Moustache in both conditions and the DSS upwind, also have the most drag, as shown upwind in Figure 8 (a) and downwind in Figure 8 (b)

    The authors note that their research is not conclusive and more is required, but they couldn't find any overall advantage for the three configurations tested over a boat without foils. The biggest benefit was in heave attenuation, which in itself doesn't make boat faster. It may make it more comfortable, so easier to drive harder but not necessarily faster.
     
    Last edited: May 19, 2019 at 8:16 AM
  4. CT 249
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    CT 249 Senior Member

    But given the enormous cost of the foils - reported at about one third of the cost of a Figaro - it would be vastly more effective to make the boat longer which would reduce pitch (the greatest contributor to seasickness) while also improving speed.
     
  5. philSweet
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    philSweet Senior Member

    Why the duplicate thread? there's a discussion already on the original.

    CT, no doubt there is a huge development cost still associated with foil systems. That should come down fairly quickly if a few more people prove themselves able to develop such systems, and deployment and seal components become standard kit. We need guidance on safety factors and impact loads both for the foil itself and for the crashbox and seal systems. We need heuristics for gust response and other perturbations. Something like AVL software for aircraft, but able to plot stability analyses on a wind polar. Once we can look at dynamic stability characteristics and performance characteristics side by side on a polar chart, these different configurations can be sized and located on the hulls much easier.

    The relative roles of active pitch adjustment and control vs elastic compliance is another item that needs sorted. This will be different for the different foil types.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    =========================
    I thought that since there are several foil assist topics here including the Figaro 3 and Baltic 142 that this was a good place to also have the topic.
     
  7. philSweet
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    philSweet Senior Member

    Maybe edit the first post to explain the broader purpose.
     

  8. CT 249
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    CT 249 Senior Member

    But Phil, the Figaro III doesn't have that sort of complicated system and the foils are STILL extremely expensive. Those fairly simple foils are said to cost 1/3 of the entire price of the boat - lengthening the hull would probably create a much better improvement in speed and motion for less cost and more convenience.
     
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