AC 36 Foiling Monohulls

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

  1. Doug Lord
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    Doug Lord Flight Ready

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    They shouldn't be. If you remember 35, it started out being the AC 62 but when they ran into objections and cost problems it was changed mid stream to the AC 50. So you never can tell especially with a concept like NZAC75.
     
  2. Skyak
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    Skyak Senior Member

    Your characterization in this post and a few previous are missing the physical trade-offs in the AC 36 rule. The T foils have distinct limits to their optimization. A foil that supported liftoff in 6 knots of wind would be at a big disadvantage at 50 knots of boat speed compared to a boat with foils to take off in 9. And at the lower takeoff speed, the drag advantage of getting the hull out of the water is smaller on this 75 ft mono. Surface piercing foils can significantly reduce area, T foils can't, and AC36 will be running up against the cavitation ceiling so the profiles will be limited to avoid pressure peaks. The biggest "innovation" in the AC 36 foils may be the flap mechanisms.

    I agree that for commercial one design sailboats, low wind takeoff is critical to marketability. The AC is NOT one design for the foils. When they tell you where the takeoff is it is because they know the boundaries and what is most likely to win. Don't imply that you know better than they do, even now before they have produced a single boat.

    I have a question for the experts- I was thinking that since weight is fixed and foil lift is abundant at top speed -will the boats run at significant negative leeway foiling at top speed? Or is the loading more critical at top speed? Would significant negative leeway make sense, and under what conditions?
     
  3. OzFred
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    OzFred Senior Member

    He's also ignoring that the AC75 Class rule is published with over 301 rules, they are very detailed. They will change over time, but they will almost certainly not include significant changes like adding central keels or wands. That discussion was vaild before the rules were released, but not now.

    Absolutely. Also, "low wind" is not a defined number.

    I'm certainly no expert, which means I'm free to be as wrong as the next person. ;-)

    I'm sure horizontal vectors are something teams are looking at very hard. It surprised me that they used downforce from the rudders last time, it was a risky strategy but clearly necessary to get the most out of the boats. It can't be done this time as there's only one rudder.

    I can't remember whether it's possible to use downforce from the windward main foil in the AC75 rules, but it certainly will be used if it's allowed. And downforce from the windward foil can also produce lift to windward (and indicates a mostly symmetric section). So there will be a lot of calculations going on to optimise lift from all foils, vertically and horizontally, and the trade–off with drag.

    It will also be very interesting to see what teams adopt for controls and feedback systems. How will they know when lift is optimised? It's gone well beyond ride height, the whole system of foils (both above and below the water) is now so complex that instrumentation and controls are essential for sailing the boats, and the team with the best electronics and control systems will have a huge advantage, just like last time.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    AC Light Air Foiling- to determine the viability of light air foiling accurately some serious number crunching needs to be done. But before that it might help if you had a target. In 35 the limit was 6 and 26. If this was to be 9 and 26 or 10 and 26 the effective windrange is getting pretty small.
    According to the Rule these boats must use flaps which will help with foil control and light air takeoff.
    The Shock 40 CBTF was capable of so-called "negative leeway"- it didn't make a lot of sense except as a tactical maneuver. I just read of a high speed boat where the designer thinks it could be beneficial.
     
    Last edited: Jun 24, 2018
  5. Doug Lord
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    Doug Lord Flight Ready

    AC Light Air Foiling- Based on the designers and manufacturers that have used light air foiling in their marketing presentation light air foiling takes place in winds between 4-6 knots. The wind limits of 35 were 6 knots for light air. You can bet that if 6 and 26 were used again the designers would find a way to takeoff and effectively foil in 6 knots. The narrower the total windrange the more likely races will be postponed for too much or too little wind.
    NZAC75 will have the capability of lowering both foils to get started and then raising the windward foil to accelerate.
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    In case it's not already in this thread here is the AC 75 Class Rule:
     

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    Last edited: Jun 24, 2018
  6. Doug Lord
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    Doug Lord Flight Ready

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    I think it's valid NOW. Recent history has shown that not only could central keels or wands be added but the whole boat could be changed as it was in 35!!
     
  7. Doug Lord
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    Doug Lord Flight Ready

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    From Scuttlebutt Europe and
    INEOS Team UK Test Boat http://www.sailweb.co.uk/Americas%20Cup/30357/ineos-team-uk-test-boat

    "Ben Ainslie's team splashed their test boat in the past few days.

    Here is INEO's yacht rigged and ready to go in the water for capsize tests. Notice the flotation attached to the top of the mast. My sources tell me they did indeed run capsize and righting tests.

    The INEOS test yacht is a modified Quant 28. The Quant 28 was designed by Hugh Wellbourn, developer of the "Dynamic Stability System" - a horizontal foil that can be extended to leeward to give a monohull more righting moment." -- Jack Griffin, CupExperience.com

    Quant 28

     
  8. OzFred
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    OzFred Senior Member

    You’re the only one who thinks that. These boats (and the AC50s) have gone well beyond simple mechanical systems like wands for ride height, that would be a huge backward step, as would adding a central keel.
     
  9. OzFred
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    OzFred Senior Member

    Downforce from the main foils is expressly forbidden by rule 26 except when the foils are either fully raised or fully lowered.
     
  10. Doug Lord
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    Doug Lord Flight Ready

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    I disagree.
     
  11. Doug Lord
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    Doug Lord Flight Ready

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    I wonder how they'll control altitude w/o some downforce now and then? Or should I say "up-flap"?
     
  12. Skyak
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    Skyak Senior Member

    The arms and the hydraulics to move the arms are provided one design, to my knowledge. It would not be hard to build in sensors to detect foul play.

    About wands/control and rule changes; TNZ won AC35 on their ability to fly foils that were harder to control, but more efficient. I think they see human control of the foils as their ticket to a long AC dynasty and any automated control as handing the cup back to the US military/industrial complex. The "challenger of record" is their hand picked toady. IMHO nothing short of an embarrassing amount of human casualties will change their rules on control.
     
  13. Konstanty
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    Konstanty Junior Member

    The speed of this boat is not shocking.
     
  14. Doug Lord
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    Doug Lord Flight Ready


  15. OzFred
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    OzFred Senior Member

    They don’t need downforce to control height, nor did the other foiling AC boats. The rules just say the foil can’t produce downforce, not that the flap can’t go up. So whether the flap is up or down is irrelevant, it’s the overall (net) force generated by the foil that matters.

    Downforce may be generated by quickly raising the foil arm, i.e. by vertical drag through the water as the foil is raised. But repeated actions to do that (I guess the articulated foil equivalent of pumping) are forbidden.

    I can’t see anything in the flap rule (14) or elsewhere that limits flap angle, up or down. Out of interest, there doesn’t appear to be any limit on rudder lift, up or down. Likely it will be capable of both in order to effectively control pitch.
     
    Last edited: Jun 26, 2018
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