AC 36 Foiling Monohulls

Discussion in 'Sailboats' started by OzFred, Sep 13, 2017.

  1. schakel
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    schakel environmental project Msc

    This vectorial drawing explains it all.
    forces ac 36.png
    How are the forces regulated that prevents the boat from pitching?
    The weigth of the crew and the mass centre of the ship provides the (purple) down force,
    together with the downforce from the (black) foiler rudder and the (green) foiler momentum, prevent the boat from a nose dive.
    The neccesarry momentum of equilibrium are the purple, black and green forces must equal the forwarding force of the sail.
    Normaly the crew is strugling to minimise heel, the strugle to prevent pitch will take equally amount of effort.
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Many foilers are set up with a rudder foil set at zero degrees and main foil at more or less +2.5 degrees. At takeoff, about 80% of the weight is on the mainfoil(s) and 20% on the rudder foil. During takeoff the boat will pitch up slightly allowing the rudder foil to lift its 20%. As the boat speeds up the rudder lift decreases and at a certain point ,as the boat pitches down slightly, the rudder foil will pull down-all automatic with a trailing rudder foil.
     
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  3. Konstanty
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    Konstanty Junior Member

    Two foils on the board and heavy and long arm canting keel should be solution. Front foil should have greater angle attack then back foil. It is easier to stand on two legs than on one.
     
    Last edited: Mar 26, 2019
  4. Doug Lord
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  5. OzFred
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    OzFred Senior Member

    Most foilers have adjustable rudder AoA because it's not that automatic. It really just follows the main foil, with trimming of its AOI adjusting the pitch of the boat and AOA of the main foil.

    Whether the rudder foil lifts up or down is based on decision of whoever is trimming it for the particular point of sail they are on, and in the case of AC50s (and maybe F50s too) whether the foil is to windward or leeward. Even your 80/20 split before foiling is just a very rough approximation and is similarly varied depending on conditions and point of sail. This stuff has been discussed ad nauseum in many forums, there really is no single set of values that applies universally.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    As I said many foilers don't have an adjustable rudder foil(while sailing) and it is NOT necessary for foiling only for racing on boats where it is class legal. For foilers that are designed to be simple to sail a trailing rudder foil that is not adjusted under sail is, without a doubt, the best way to go since it is less work for the crew and works automatically.
    The 80/20 split is not "mine" it is hydrodynamically correct for foilers designed with an "airplane" configuration according to Dr. Sam Bradfield. It can vary from around 75 to 85. The idea is to keep the trailing rudder foil lightly loaded which aids automatic pitch response. There is an illustration, that I can't find now by Martin Fisher, showing an AC 50 with a 75/25 loading.
    There are other configurations but generally the main foil is near 80% of the load and rudder foil near 20% for this configuration. On a racing boat the pitch attitude of the whole boat can be adjusted with the rudder foil within limits of the rule-that's how the AC 50's sailed with a nose down attitude.
    -------------------------------------------
    By the way, in the AC75 sketch above(post 646) the mainfoil is shown carrying 78.1% of the load at takeoff and the rudder foil is shown carrying 21.9% of the load at takeoff. As the boat speeds up the rudder lift decreases until, at some point, the rudder is pulling down.
     
    Last edited: Mar 29, 2019
  7. Doug Lord
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  8. OzFred
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    OzFred Senior Member

    It seems the number of challengers is back to where it was last year, with the remaining 3 late comers all looking like dropping out:

    America's Cup 2019: Disaster as three challengers set to withdraw

    Also not good for ETNZ financially as they'd hoped to make a few dollars by selling design packages. Still, it will be a great event if the remaining 3 challengers all make it to the start line.
     
  9. OzFred
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    OzFred Senior Member

    Incredible, really. How do you derive such precise values from a rudimentary sketch with no dimensions, in unstated conditions, with zero details of foil shape or sizes, or boat speeds, or even accurate proportions? There is no indication of transition speeds or conditions, the main foils are in very much the wrong location (if the NYYC mule is anything to go by) yet you can extrapolate precise values anyway. The only values provided are the head and main sail areas. Fascinating.

    The centre of effort (CoE), which is a significant contributor to pitching, is greatly controlled by sail trim. The "automatic" pitch stability of the rudder foil only operates in a narrow band, something like Hooke's law. Stray outside the band and all bets are off. The main foil will be actively trimmed the whole time, which which will have a significant pitch attenuation effect. The rudder foil will also be actively trimmed, but likely to a lesser extent.

    The sketch has the main foils too far aft. The NYYC mule's foils are almost abeam the mast putting them well in front of the CoE of the mainsail. The INEOS boat has the foils well ahead of the mast, so hugely ahead of the mainsail CoE and possibly of the combined CoE. No one has built an AC 75 and there are few constraints on where the foils must be located or their relation to the rig, so you have as much idea of the foil locations, moments, load distribution, etc. as the rest of us (i.e. very little). They are nothing like an AC50.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    The foils are placed with respect to the CG. Sails are placed with respect to the already determined position of the foils. Hookes Law is not relevant to the rudder t-foil as best I can tell-it's loading is the determining factor of it's response. The rudder t-foil can operate in a fairly wide range from carrying 20% of the load to pulling down substantially.
     
  11. Doug Lord
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    ==================================
    Pressure Drop - Rumors Of Withdrawals False Say ETNZ http://www.pressure-drop.us/forums/content.php?9093-Rumors-Of-Withdrawals-False-Say-ETNZ
     
  12. Doug Lord
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    Doug Lord Flight Ready

  13. Doug Lord
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    And from Pressure Drop comes this:

    SOURCE: Stars + Stripes Team USA

    Long Beach Yacht Club’s Challenge for the 36th America’s Cup presented by Prada, Stars + Stripes USA, has not withdrawn from the America’s Cup and has no plans to do so. In addition to continuing its preparations for AC36, the Stars + Stripes team is racing this week in the 55th Congressional Cup hosted by Long Beach Yacht Club. Racing alongside team co-founder Taylor Canfield as part of his co-ed team will be Sally Barkow, George Peet, Jesse Fielding, Ben Bardwell, and Stars + Stripes team member Mike Buckley as tactician.

    LBYC leadership along with Stars + Stripes team leaders Mike Buckley and Taylor Canfield have doubled down on their All-American challenge and will continue to push to the end. The team has made structural changes recently and Mike Buckley will be becoming the CEO of the team. In addition, the team has recruited additional top-flight America’s Cup management, marketing and fundraising talent, including some from Dennis Conner’s victorious Stars & Stripes 87 team, to join the team and its Advisory Board.

    “The Stars + Stripes team and Long Beach Yacht Club have redoubled their commitment-to-the-commitment, as Dennis Conner was fond of saying, inspiring his Stars & Stripes 87 team to its victory down under,” said Mike Buckley, Skipper SSUSA.

    “What Mike and Taylor have created has resonated with the American sailing population. We are seeing this first hand here within the community of Long Beach” said Camille Daniels, Commodore LBYC.
     
  14. Doug Lord
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    Doug Lord Flight Ready


  15. Doug Lord
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    Doug Lord Flight Ready

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