Erwankerauzen

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11 Whiner

About Erwankerauzen

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  1. Erwankerauzen

    Moth Developement

    Thanks Daniel Now I understand; It makes sense for sure. Cheers Erwan
  2. Erwankerauzen

    Moth Developement

    Sorry Dave, Although I understand the words, I think I do not understand the meaning in deepth. Cheers Erwan
  3. Erwankerauzen

    Moth Developement

    Thanks Doug for your elegant and synthetic approach Thanks PhilS, I had no idea on how big were (are) the hull, I assumed same size, which obviously was not a good assumpstion. Cheers and Fair Winds
  4. Erwankerauzen

    Moth Developement

    Sorry for the bad wording It is not clear or even wrong But I am sure you understand what I mean Cheers
  5. Erwankerauzen

    Moth Developement

    According to the workpaper, if the hull lift is 17 lbs then the driving force of the lift is the projection of the lift on the AW direction so if the angle is around 20° then 17lbs x sin 25°= 25N But you are right, I do consider the loss of theorical lift due to the tiny aspect ratio of the sail which probably offset a big if not all part of the theorical lift. Without this 25 N lift pick-up, the global drag of the hull is even worse. Thanks for this positive contribution, Cheers
  6. Erwankerauzen

    The new sailing twin skin setup

    Thanks for searching, I know there is a ton of workpapers addressing morphing wing to replace flaps Cheers
  7. Erwankerauzen

    Moth Developement

    Hi Everybody, Regarding the "Moth Development" in the Beaver workpaper (about 10 years old now), I noticed something interesting: They tested the aero drag of the Moth plateform with and without a dummy crew, on an aerodynamic balance. And they measured someting like 17lbs "lift" and 10 lbs "drag" But the "lift" of the hull increases the heeling moment,; Although the hull's lift is low compared to the sail's CoE, it still contributes to offset a part of the crew righting moment., so it creates a little give-up in driving force. That is why it may deserve to crunch some figures in order to see the impact of the hull aero on the driving force. With my hand computer on my smartphone please find below the rough figures I could suss out: Hull lift = 75Newtons @1 meter above the foil Center of Lift : Hull Moment = 75 N x meter The sail creates around 375N @ 4 meters above the foil: Sail Moment = 1500 N x meter It is only a 5% give up in righting moment which translate in a 5% give-up in driving force Sail driving force = 125 N @ 20° apparent wind , the driving force give-up is around 6 N The hull drag at 7 lbs is equivalent to 44 N which is a significant part of the driving force. Finally the driving force from the 17 lbs hull's lift is around= + 25 N So the net result is 25N -6N -44N=- 25 N to be compared with the 125 N sail's driving force Hope it is not too boring to read and do not hesitate to bring comment & critics Cheers
  8. Erwankerauzen

    C-Class Little Cup news

    Revintage, Thanks for the workpaper Cheers
  9. Erwankerauzen

    A-Cat Style Rig on foiling Moth

    an A-Cat mast section is about 900g/meter weight while a 6 meters Moth mast is around 2.2 kg So just the weight is a problem Try a single element morphing wing instead, as there is no correlation between mast stifness and wing sections, so no plenty of mast & sail iterations, and no vang, no cunning, no leech pulley block.. Cheers Erwan
  10. Erwankerauzen

    Hervey Bay A Class Worlds

    I am not sure you have anything laminar above 6 knts TWS in the wind boundary layer above water surface I assume the BL Turbulent from leading edge to trailing edge, both faces (ie:transition point @0% chord). Cheers to all the Happy Aussies who have strong winds when they go sailing
  11. Erwankerauzen

    Hervey Bay A Class Worlds

    Thanks for the remarks, find attached a document which mention sail roughness 10 micrometers is mentionned If the higher the apparent wind the thinner the boundary layer, I am not sure of this theory, but if relevant, may be the new A-Cat performances, could make this issue more relevant than for the classic. Congratulations for the champions Cheers Sail_Roughness.pdf
  12. Erwankerauzen

    Hervey Bay A Class Worlds

    Thanks to All of you for these interstinng reports & comments. Regarding the sail's shape, I can make the following comment which is a straightforward consequence of the apparent wind: Not too full at the bottom is the best trade-off according to the wind twist downwind and wind gradient windward. Now, regarding "surface roughness" of the sails, it seems to me, according to the pictures available on the forum, that: Ashby sails seem to be made mostly with horizontal panels and horizontal seams, minimizing fabric overlaps and other seams @ 90° to the air flow. Honestly, I guess it should be a competitive advantage for drag, probably not much, but a little gain here, can trigger another little gain there, and starts a virtuous circle. Just an idea, I can be wrong so don't throw me stones if you do not agree. Cheers
  13. Erwankerauzen

    The new sailing twin skin setup

    Kiwing, If your above-mentionned readings are not secret, I am sure many geek loke me would be happy to read then too. Could you post some reading reference please. Thanks in advance Laurent Erwan
  14. Erwankerauzen

    Hervey Bay A Class Worlds

    Thanks Happy week-end
  15. Erwankerauzen

    Hervey Bay A Class Worlds

    Thank You Everybody for these precious semantic details. Fair winds to all Erwan