AC 36 Foiling Monohulls

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

  1. Doug Lord
    Joined: May 2009
    Posts: 16,384
    Likes: 282, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    ==================
    Joseph, I'm not sure that the stability of the NZAC system is good enough for ocean racing. I'd bet that the foil system being pioneered by the newest IMOCA 60fters would be if it was modified to allow rudder t-foils so the boats aren't dragging their behinds as they do now. Unfortunately, rudder T-foils are illegal in the IMOCA Class due to a quirk in the rules-something I'd bet will be changed before too long. Once the t-foils are added the resultant full flying foiler would be fully self-righting. Now, the boats are using "foil assist" and do not fully fly.
    also see: New Record for the Boss, Hugo Boss that is... https://www.boatdesign.net/threads/new-record-for-the-boss-hugo-boss-that-is.61339/


    IMOCA Charal:
    CharalDefiAzimut2018byYvanZedda_52.jpg

    CharalDefiAzimut2018byZedda_06.jpg
     
  2. OzFred
    Joined: Nov 2015
    Posts: 432
    Likes: 40, Points: 28, Legacy Rep: 16
    Location: Earth

    OzFred Senior Member

    The "common hull spec" is a box rule (more–or–less), it leaves plenty of room for individuality. There is a standard package (design?) available for those who don't want to start from scratch, perhaps two teams will use it.

    There is no common foil spec. There is a (6 sided) box rule and some minor design constraints.

    The foils weigh 1.2 tons each, the arm and stock weighs another 1.1 tons. The foil control system is another 365kg. The foils don't retract, they swing up and down. I don't think anyone is going to be removing them while on the water.
    I like your positivity, but the configuration is impractical for anything other than a regatta like the AC. Longer races will require the battery power unit to be supplemented or replaced by a fairly substantial fuel engine that runs all the time to support the foil and sail control systems. It's one reason why boats like Wild Oats XI don't do many long races, and I expect the AC 75s will use a lot more power to raise and lower the foil arms and foils and trim the flaps and sails.

    They are also way under ballasted in displacement mode, which they will be forced to adopt in relatively modest storms. A cruising 75' yacht will likely have a displacement around 50 tons, AC 75s displace just 7.6 tons, which is somewhere beyond diabolical. They are extremely unstable when not foiling, with fairly restricted conditions where they can foil, maybe less than 40kn of breeze in other than smooth or protected waters.

    Considering the performances of the solo crewed 100' multi–hulls, these lizard–legged monos have a lot of catching up to do. :)
     
  3. schakel
    Joined: Jul 2008
    Posts: 347
    Likes: 9, Points: 18, Legacy Rep: 48
    Location: the netherlands

    schakel environmental project Msc

    And here is the catch: When you have a crew of 10, lifting all at once a halter of 2.3 ton, how often can they repeat that if they make it at all?
    And the amount of energy needed to lift a foil is under estimated in this calculation since the foils are swiveled with internal friction.

    External electro motors like used in the dog fight of 2010 is not allowed.
    So how on earth will the crew be able to perform such a heavy weight lifting?
    World record heavy lifting is 264 kg.
     
  4. Earl Boebert
    Joined: Dec 2005
    Posts: 351
    Likes: 34, Points: 28, Legacy Rep: 302
    Location: Albuquerque NM USA

    Earl Boebert Senior Member

    According to the video of the test rig released by ETNZ, the foils are not electrically actuated:



    As far as I could tell from the description, and I could be very wrong here, the system is based on hydraulic accumulators. A charged accumulator raises the arm by transferring hydraulic fluid to a piston. When the arm drops by gravity, the fluid returns to the accumulator and (I presume) partially recharges it. The accumulator is "topped off" with pressure from a "pre charge tank." It appears (more speculation) that the limiting factor is the capacity of the "pre charge tank," not the amount of juice in the on-board battery.

    The narrator asserts that an arm can be lifted in 3 seconds; timing the video shows the test rig doing it in 6-7 seconds. A 3 second lift has interesting implications for the stress on the arm, particularly as the foil transitions from water to air. But that's another topic.

    Cheers,

    Earl
     
  5. Doug Lord
    Joined: May 2009
    Posts: 16,384
    Likes: 282, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    More-their target is " hopefully 3 seconds" :
    (about 5 seconds in this video)
     
  6. Earl Boebert
    Joined: Dec 2005
    Posts: 351
    Likes: 34, Points: 28, Legacy Rep: 302
    Location: Albuquerque NM USA

    Earl Boebert Senior Member

    So we're talking 6-10 seconds to execute a tack or gybe. That's a lot of distance at 50kt.

    Cheers,

    Earl
     
  7. Doug Lord
    Joined: May 2009
    Posts: 16,384
    Likes: 282, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    Seems like he said it takes 15 seconds to recharge which would make it a minimum of 18 seconds assuming the lifting foil did so in 3 seconds?
     
  8. Earl Boebert
    Joined: Dec 2005
    Posts: 351
    Likes: 34, Points: 28, Legacy Rep: 302
    Location: Albuquerque NM USA

    Earl Boebert Senior Member

    Well, 50kt is 84 ft/sec or, more interestingly, 1.15 boat lengths/sec. So to do a full "twaddle" ("tacking waddle" -- up leg to down and down leg to up :)) would take how much distance?

    Cheers,

    Earl
     
  9. Doug Lord
    Joined: May 2009
    Posts: 16,384
    Likes: 282, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    Seems ridiculous but I'm sure he said 15 sec. I'll listen again when I have time. Is that what you heard?
     
  10. JosephT
    Joined: Jun 2009
    Posts: 804
    Likes: 90, Points: 28, Legacy Rep: 218
    Location: Roaring Forties

    JosephT Senior Member

    Was a reason provided for not using a T foil design?
     
  11. Doug Lord
    Joined: May 2009
    Posts: 16,384
    Likes: 282, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    I think I remember that it was cost, but I'm not sure. Whatever it was did not impress me at all.
    I don't think "they" envisioned what has proved possible already with the sixties much less actually flying. The jump to the current foils was a big one for the class- a jump to full flying would have been a jump too far for many. Now, however, a jump to rudder t-foils is simply the final step, not a big jump. Just a matter of time,I think.
    Imoca class rules 2017 https://www.boatdesign.net/threads/imoca-class-rules-2017.59147/
    News - Foils on the IMOCAs – what the designers think - Vendée Globe https://www.vendeeglobe.org/en/news/14914/foils-on-the-imocas-what-the-designers-think
    IMOCA 60 2016-2017 Foil Assist https://www.boatdesign.net/threads/imoca-60-2016-2017-foil-assist.55381/#post-771554
     
    Last edited: Jan 18, 2019
  12. JosephT
    Joined: Jun 2009
    Posts: 804
    Likes: 90, Points: 28, Legacy Rep: 218
    Location: Roaring Forties

    JosephT Senior Member

    I agree...seems to be just a matter of time. Here's a narrower T-foil and T-rudder I bumped into (includes a wipeout at 1:10).

     
    Doug Lord likes this.
  13. Earl Boebert
    Joined: Dec 2005
    Posts: 351
    Likes: 34, Points: 28, Legacy Rep: 302
    Location: Albuquerque NM USA

    Earl Boebert Senior Member

    Yes. I took to mean that after you did a lift it was 15 seconds before you could do another one. I couldn't figure out if that was per side or per system. In other words, did he mean that if you dropped the starboard leg it would be 15 seconds before you could lift the starboard leg, or that if you dropped the starboard leg it would be 15 seconds before you could lift either the port or starboard legs. Looked at from a configuration perspective, is there one set of accumulators per arm, or one set that powers both arms. In either case the effect on tactics will be profound.

    Cheers,

    Earl
     
    Doug Lord likes this.
  14. Doug Lord
    Joined: May 2009
    Posts: 16,384
    Likes: 282, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    I think it has to be one set per arm but I'm not positive though I think they'll be many situations where both arms will need(want) to move simultaneously.
     

  15. OzFred
    Joined: Nov 2015
    Posts: 432
    Likes: 40, Points: 28, Legacy Rep: 16
    Location: Earth

    OzFred Senior Member

    Sorry, I was wrong there (late night posting…). In the current rule, each foil is 970kg and arm 245kg, so 1.215 tons total for the foil and arm.

    The capacity of the battery is a factor in that it must hold enough energy for all the lifts and drops in a race (less whatever is recovered from a drop), plus the other systems it supplies energy for. It must also be able to discharge energy fast enough. I don't think those are issues for AC length races, but they likely are for long distance (say 15 to 20 day) races so an alternative energy source would be required.

    The system has to work within design parameters, so there will always be something that is seen as the limiting factor. The accumulator helps lift the foil, so a bigger accumulator should lift faster (I guess). A bigger accumulator needs more energy to charge it, so longer charge time or a higher capacity pump is required. So weight probably goes up and so on…

    Some engineers worked on the one in the video for 6 months and still had some way to go to reach their target of a 3 second lift. A target cycle time wasn't mentioned, but 15 seconds seems a bit long. There are practical limitations to how fast sails can be tacked and speed recovered to sustain foiling, maybe a 10 second cycle time is enough?

    There is only one foil control system, but it's not clear if there are two accumulators or one. It would make sense to have two so boats could do two tacks or gybes fairly quickly (and one can be a backup for the other in an emergency), before being limited by recharge times. It's also not clear if the foils need to be fully lifted each time, e.g. it may be possible to leave both foils down and do multiple gybes as quickly as the crew can do them. High frequency tacking and gybing hasn't been a factor in the last couple of cups so maybe it's not considered necessary for this one either.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.