Can a Pacific Proa Benefit From Lifting Foils ?

Discussion in 'Multihulls' started by mcm, Feb 5, 2015.

  1. tspeer
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    tspeer Senior Member

    The computer says those sections would work OK. But I have my doubts as to whether they would work well in practice. I would be inclined to go with a sharp-edged section for a real design, despite the potential for ventilation.
     
  2. cavalier mk2
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    cavalier mk2 Senior Member

    I think Bernard might have too much cheese in the mousetrap for that boat to do well in the varied conditions of the real world.
     
  3. tspeer
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    tspeer Senior Member

    It looks like you have the windward foil angled to provide an upward force. This will add to the heeling moment. I think it would be better to angle it the other way, so it has a downward vertical force. This will let you load up the rig more.

    Controlling the incidence of the windward foil would allow you to maintain a constant heel angle.

    Breeching of a downward-lifting foil can lead to a significant emotional event, however.
     
  4. mcm
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    mcm Senior Member

    That's Timothy's 'New Wave' design, and i'm not sure how he's going to deal with the diminished righting moment caused by the cant of his windward foil.

    Tom, with that in mind, and with my desire to fly the vaka, what do you think of 'cavalier's' idea of eliminating the ama foil altogether and replacing it with a banana foil in the vaka.

    Originally, i was thinking of a wand adjusted t-foil on the ama in order to both lift the ama and increase the righting moment at the same time.

    Righting moment is of course a critical issue with pacific proas.
    And if i sacrificed having a foil in the ama that increased righting moment for a foil in the vaka in an attempt to lift the vaka, then i would have to add ballast to the ama to regain some righting moment.


    But if it's a wand adjusted t-foil, then by the time it begins to breech it would have adjusted from a downward-lifting foil to a lifting foil,,, no ?
     
  5. mcm
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    mcm Senior Member

    Do you mean a sharp leading edge ?
     
  6. cavalier mk2
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    cavalier mk2 Senior Member

    An Atlantic proa is really well suited to a banana ama foils and mainhull t foil rudders. Then it is working like a tri for sail carrying power but again you don't want to get caught aback. Pacific proas were intended to use live ballast to make the idea work. Water ballast in a sliding car comes to mind similar to some of the old Capt. Nat sailing machines.
     
  7. redreuben
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    redreuben redreuben

    And then there are the Harry's :D
     
  8. cavalier mk2
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    cavalier mk2 Senior Member

    Harrys are Pacific......The old log ama has merit in a pacific, small section to wave pierce as it lifts the water doesn't carry the weight so it increases as ballast till it is fully flying. You don't want to get caught aback but it would be easier to right forcing the log down.
     
  9. mcm
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    mcm Senior Member

    Sure, but then your just in pacific proa mode but with greater righting moment.

    But remember the Gougeon Bros. proa, 'Sling-Shot' ? It had sliding ballast, and they said it was a real difficult boat to sail.
     
  10. mcm
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    mcm Senior Member

    Now, about Rob's 'Bucket List', with no foils but the two rudders how does it resist leeway ? Do the rudders have to take on the leeway resistance loads and provide a balanced helm too ?
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    The question would be how did they control it.
     
  12. cavalier mk2
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    cavalier mk2 Senior Member

    That is the idea about Bucket List.
     
  13. redreuben
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    redreuben redreuben

    If Tom Speer's bidirectional rudder can provide lift in both directions could it be used as a J foil ?
     
  14. Timothy
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    Timothy Senior Member

    The model I built originaly had two canted retracting asymmetrical foils optomised for each direction on a safety ama and two conventional Clark y sectioned retractable rudders quarter hung on the windward side of the aka. Only the forward foil and the aft rudder were deployed.I would have used banana foils but could not figure out where to put them with the boat folded. The foil on the ama in the rendering is a mistake. I am currently experimenting with ways to make my weight target and reducing the number of foils and their attendant hardware from four to two seems like it might help. Right now, like the OP, I am trying to determine weather or not the lifting foil is worth the bother. It seemed to work on the original model. But although the boat did maintain a bow up attitude with the foil,when I removed it I think the model was just as stable and perhaps faster with the bow level. However in order to save weight I have since narrowed the over all beam, changed from a safety ama to a flat bottomed pod, and therefore reduced the Rm. So although I have also reduced the size of the rig, and lowered the centre of effort I think that now I will definitely need a lifting foil to leeward to keep the model upright. In the end I think I might find that the Bucket List wide beam weight to windward two foil configuration is the way to go.
     

  15. cavalier mk2
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    cavalier mk2 Senior Member

    The Newick dagger/rudders do have some strength and endplate advantages over leeboards in a 2 foil configuration. If I was doing the basic race setup I would go with the Atlantic configuration with the ama banana foils like a tri racer. The t-foil rudders would need some mounting thought, perhaps using my CARD sleds. If you think about it you wind up with the same amount of foils and rudders as a racing tri that has a banana in each ama and up to 3 rudders but you are still 1 ama lighter in a proa. A vaka pod and caught aback sheet release would make things safer.
     
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