AC 36 Foiling Monohulls

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

  1. Konstanty
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    Konstanty Junior Member

    It is not good to put ballast in foil. For the ballast movement, the previously proposed solution may be: AC 36 Foiling Monohulls https://www.boatdesign.net/threads/ac-36-foiling-monohulls.59160/page-27
     
  2. Doug Lord
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    Doug Lord Flight Ready

  3. Doug Lord
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  4. OzFred
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    OzFred Senior Member

    An interesting article on Giornale della Vela comparing the 3 hulls launched so far:

    Luna Rossa:
    [​IMG]
    ETNZ:
    [​IMG]
    American Magic:
    [​IMG]
    I thought the biggest differences would be above the waterline and that below they'd all look like American Magic. Seems it's the other way around, except for the bows. I expected some big differences in foils, but LR has some pretty surprising features (I have no idea what the pods near the outer third of the foils are for).
    [​IMG]
    Image from Sailworld.
     
  5. Dolfiman
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    Dolfiman Senior Member

    A small mass to change the vibration frequency ?
     
  6. OzFred
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    OzFred Senior Member

  7. wet feet
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    wet feet Senior Member

    A couple of points in reply to OzFred; I can't really distinguish any part of those hulls as "keels".In fact the arms for the foils would seem to come closest to the usual definition as they provide lateral plane and ballast.As for who might have it right, that will probably be revealed quite quickly when the racing starts.One that appears to have made an odd choice is the British boat-I just can't see those abrupt ends of the recess by the keel arm roots being helpful in any way and it seems the designers of the other boats have added fairings that ought to be less "draggy".Maybe somebody here can confirm my suspicion that the bulbs on the foils are likely to contain some transducers for tactical or performance related electronics.

    One thing I am becoming curious about is the planform of the rudder foils as not all of them have been revealed.Come to that,why has the Ineos Team UK boat got an inverted V in the frontal view of the rudder foil?
     
  8. OzFred
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    OzFred Senior Member

    The use of "keel" is in the traditional sense of the main structural member of a boat running from stem to stern on which frames were mounted. Originally it had no hydrodynamic purpose. The term is still used in the class rules of various dinghies where the "keel" is simply a longitudinal line down the centre of the boat. It may not be distinguishable from the adjacent hull surface other than being aligned with the stem, centreboard case and rudder.

    Fairing of the arm recesses does seem like a good idea. Even if the drag is insignificant, it's got to play on the minds of the crew every time they feel they're lacking in speed in displacement mode.

    The "inverted V" rudder joint is pretty standard and is used on F50s and at least some of the AC50s (and I think some Moths). It reduces turbulence and drag at the joint. Only the region around the joint is anhedral because on a foiler designed to be sailed flat, there's no point having an anhedral rudder. As always, there are compromises and tradeoffs. ;-)
     
  9. Mertens V.
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    Mertens V. New Member

    The guys over at Vittorio d'Albertas's youtube channel(Vittorio d'Albertas https://www.youtube.com/channel/UCafRkugGEmzs_mygEHewlmwp), suggested that maybe the bulbs are only there for foil-testing. The ac75-class-rule states that you can only make 6 different foils in total, but you can modify a foil as long as you are only making changes to 20% of its mass. So maybe the bulbs are only there for the weight. This way the teams can try different foil-shapes/configurations without 'sacrificing' one of their six total foils. What do you guys think ?
     
  10. Tiny Turnip
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    Tiny Turnip Senior Member

    The raised foil would seem to present a notably increased risk of injury/death in collision. Closing speeds of what, possibly 120 mph on opposite tacks? Hard to judge fine distances between the boats at that speed. Id be after them all being hi viz orange.
     
  11. CT249
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    CT249 Senior Member

    On the other hand, millions of car drivers encounter similar closing speeds hundreds or thousands of times a day when they pass oncoming traffic, and they normally miss each other. And plenty of amateur cat and windsurfer racers encounter closing speeds in the order of 40-80mph or more with very few closing collisions. The Defi Wind windsurfing race can get over 1000 competitors, doing a zig-zag course in high winds at high speeds and there don't seem to be big collisions.
     
  12. Dolfiman
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    Dolfiman Senior Member

    This ETNZ video of the first day sailing, the protuberant "keel" line seems to play a role in the transition phase :
     
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  13. Earl Boebert
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    Earl Boebert Senior Member

    (Replying to CT249 above) Except there appear to be limitations on maneuverability imposed by the (relative to speed over water) slow motion of the foil arms. I don't see how you're going to do a crash tack in one of these things, as the RM depends on the windward arm being up. And there's also the question of a possible mandatory interval between foil arm motions imposed by the need to top off the accumulator charge.

    Like everything else about these vehicles, only time will tell.

    Cheers,

    Earl
     
  14. wet feet
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    wet feet Senior Member

    The ENTZ video is interesting in that the foil arm seems to produce more of a bow wave then the main hull does.Would this be a Reynolds number related thing? The amount and disposition of rocker makes the touchdown happen with a positive angle of incidence-presumably to avoid digging in too suddenly.

    One thing all the boats seen so far have in common is they have been faired superbly-not a ripple or bump anywhere to be seen. Some good work went on there.
     

  15. OzFred
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    OzFred Senior Member

    Difficult to judge as the boat is being towed onto foils. There are essentially 3 different hull shapes, we'll know more about which transitions better when they start racing each other. There is a lot of learning to do on technique and with the different hulls, each might go about it differently. Or not.

    ETNZ might be towing onto foils so as to not reveal their strategy for transition, or they just haven't worked out how to do it in light winds yet.

    I don't think it's an issue for AC sailors, however in the hands of a weekend warrior it would certainly be an issue. But they aren't likely to ever be able to afford anything like AC75–style foils, nor find anyone to race for quite some time.
     
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