A Class Cat with automatically canting daggerboards

Discussion in 'Multihulls' started by Doug Lord, Jul 18, 2017.

  1. Doug Lord
    Joined: May 2009
    Posts: 16,524
    Likes: 291, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Last edited: Jul 18, 2017
  2. bjn
    Joined: Jul 2014
    Posts: 135
    Likes: 8, Points: 18, Legacy Rep: 16
    Location: Stockholm

    bjn Senior Member

    Seems interesting, but I couldn't find the video
     
  3. Doug Lord
    Joined: May 2009
    Posts: 16,524
    Likes: 291, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    You have to scroll about two thirds of the way down and look for the July 11th and July 9th posts with pictures and video....
     
  4. Nico Crispi
    Joined: Jun 2017
    Posts: 47
    Likes: 2, Points: 8
    Location: NE FL & SOCAL

    Nico Crispi Junior Member

    Any other sites for those of us who don't Failbook?
     
  5. Doug Lord
    Joined: May 2009
    Posts: 16,524
    Likes: 291, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    I'm not a member of and don't use facebook but this particular page opens fine......
     
  6. bjn
    Joined: Jul 2014
    Posts: 135
    Likes: 8, Points: 18, Legacy Rep: 16
    Location: Stockholm

    bjn Senior Member

    Video:
    Foiling Week https://www.facebook.com/foilingweek/videos/855820077927862/?hc_ref=ARSkE4mute9yyfKSq1v-qKpVpifCs_C2IzlziHOKxo3DwbdvdQ04kEr8Ub_9PNysVpg

    Pictures:
    International A-Division Catamaran Association https://www.facebook.com/permalink.php?story_fbid=1143248695819655&id=180972642047270

    He says the leeward foil creates vertical lift (lifts boat out of water), and the windward creates horisontal lift / leeway prevention. But is it as fast as the fixed Z-foils? (DNA, etc.)

    I'm concerned about how efficient the windward foil can be used for leeway prevention, since it has an asymmetrical profile. That profile will naturally push the boat in the same direction as the sail. To push in the other direction, it has to be used with a negative angle of attack, which means the boat has to sail "sideways". (More sideways than a boat with symmetrical daggerboards or assymetrical in the right direction.) That seems draggy to me.

    It's nice if it's more stable. Did I understand that the stability is simply because the foil is used kind of like a "bruce foil"? Like Hydroptere?
     
  7. Doug Lord
    Joined: May 2009
    Posts: 16,524
    Likes: 291, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    As I understood it , it is more stable than "Z" foils(according to Thilo) because the windward foil doesn't develop vertical lift. "Z" foil boats develop vertical lift on both main foils , reducing RM.
     
  8. Doug Lord
    Joined: May 2009
    Posts: 16,524
    Likes: 291, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

  9. bjn
    Joined: Jul 2014
    Posts: 135
    Likes: 8, Points: 18, Legacy Rep: 16
    Location: Stockholm

    bjn Senior Member

    I was talking about heave stability. Listen at about 7 minutes.

    And I'm not convinced about RM. The tilted board is more inboard, reducing RM.

    With double Z-boards I assume the windward one is not developing significant lift. Since leeway puts the windward foil at a negative angle of attack. Otherwise those boats wouldn't work very well.
     
  10. Doug Lord
    Joined: May 2009
    Posts: 16,524
    Likes: 291, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    "Z" boards have low roll stability compared to other foils. Read Martins interview in www.catsailingnews.com with Bora Gulari about the N17 where he said words to the effect that the roll stability of a "normal" catamaran is gone -it's like being on a teter toter*........
    I'm not convinced of the viability of Thilo's system particularly in rough water but I wish him luck.
    Performance Sailing & Nacra 17 Foiling Gybes: Q&A with Bora Gulari | Catamaran Racing, News & Design http://www.catsailingnews.com/2017/04/performance-sailing-nacra-17-foiling.html

    * Going to be interesting to watch the TF10 development-two very deep "Z" foils.
     
    Last edited: Jul 25, 2017
  11. OzFred
    Joined: Nov 2015
    Posts: 458
    Likes: 43, Points: 28, Legacy Rep: 16
    Location: Earth

    OzFred Senior Member

    Bora was comparing foiling to a displacement catamaran, you can't extrapolate from that to some generalisation that Z foils have less roll stability than other foil shapes. Also, the Z foils used on A Class boats are completely different to the Nacra Z foils (not to mention they are very different boats).
     
  12. Doug Lord
    Joined: May 2009
    Posts: 16,524
    Likes: 291, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Sure you can if you understand how other foils work. UptiP foils with the windward foil retracted and wand based foils such as on the S9 and Whisper have great roll stability compared to "Z" foil equiped boats.
    The steep angle of "Z" foils clearly has less resistance to roll than the foils mentioned above.
    "Z" foils have advantages over UptiP foils in ease of handling because the foils can be left down but wand based foils probably are the easiest to handle of any foil system because the foils actively resist roll and can add to RM.
     
  13. OzFred
    Joined: Nov 2015
    Posts: 458
    Likes: 43, Points: 28, Legacy Rep: 16
    Location: Earth

    OzFred Senior Member

    You're evading the point.
    You've taken a comment completely out of context to support an argument that you don't make any case for. You have never sailed any of the boats you mention, nor can you point to an actual comparison of them with regard to roll stability. You're just making assertions with an appeal to authority through an unrelated remark.
    If you want to make a case that Z foils are less roll stable (based solely on your own theories since you have zero actual experience), fine, go ahead. But leave Bora's comment out of it as he wasn't comparing Z foils to other foils.
     
  14. bjn
    Joined: Jul 2014
    Posts: 135
    Likes: 8, Points: 18, Legacy Rep: 16
    Location: Stockholm

    bjn Senior Member

    It seems reasonable that the Nacra foils have low roll stability, because the foils (except the small tips) follow more or less an arc of a 1.1m radius. So it should be like riding a tube with a 2.2m diameter.

    With L-foils (both down) it should be a completely different story, since the horisontal part should resist roll quite a lot.

    Z-foils (with distinct "kinks") should be somewhere in between.
     
    Last edited: Jul 26, 2017

  15. Doug Lord
    Joined: May 2009
    Posts: 16,524
    Likes: 291, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    N17 and A Cat "Z" foils:

    A Class "Z" foil: picture from acat.org
    A Class Z foils.jpg

    picture from catsailingnews.com:
    AClass Z foils.jpg

    picture from catsailingnews.com:
    NACRA 17  Z foils.jpg
     
    Last edited: Jul 26, 2017
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.