Can a Pacific Proa Benefit From Lifting Foils ?

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

  1. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    Can lifting foils benefit a pacific proa's pitch stability and lift its displacement out of the water ?

    The pacific proa usually has three foils: a leeway resisting foil on its windward ama, and two rudders on the vaka main hull.

    The big question seems to be whether the rudders on the vaka can take the lifting loads and still allow for an easy and responsive helm ?

    Fortunately the majority of the leeway load is taken up by the ama's own foil, and the ama already flies easily simply by the heeling moment.

    So i was curious if canted t-foils quarter mounted on the vaka's lee-side could both lift and effectively steer ?

    Needless to say that an end-for-end shunter with a-symmetrical rudder foils would have to fully rotate to operate in the opposite direction.
     
  2. Doug Lord
    Joined: May 2009
    Posts: 16,653
    Likes: 322, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    What do you hope the foils could do for the boat?
     
  3. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    Fly the vaka while maintaining pitch stability.
     
  4. Doug Lord
    Joined: May 2009
    Posts: 16,653
    Likes: 322, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    I think if you used one of Tom Speers proa foils you might be able to reduce the wetted surface by lifting the main hull but it seems like the lifting foils would have to be the same area and the same distance from the CG. The question is how to get pitch stability. Both rudders would have to rake back and forth.The biggest problem I see is getting some degree of altitude control. By using the foils as "foil assist" the hull still stays partially in the water so you wouldn't need altitude control(theoretically). On a "normal" foiler it's simple: you design the forward main foil to carry 80% of the weight and the rudder foil 20% of the weight. You set the main foil at +2.5degrees and the rudder foil at zero degrees and use a wand for altitude control. That is a formula for flight with excellent pitch control. I don't know how it could be done on a proa but I'll bet Tom Speer would have a suggestion. He's a member here or you could just google him and send an e-mail.

    Here's a link to his site: http://www.tspeer.com/ Scroll down to "Hydrofoils" and to the Proa foil section.......
     
  5. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    Doug, thanks for your response.

    I appreciate the work you do on foils, and your experiments with 'Fire Arrow'.

    I'll re-check Tom Speer's proa info, but i don't think the fore and aft symmetry of his foils for proas are as efficient as a-symmetrical foils and wouldn't be necessary if the foils can fully rotate on a shunt.

    The quarter hung rudders on a proa are usually hung off the beams, but usually to windward rather than my idea of leeward hung t-foil rudders canted to windward.

    Fortunately, many proas and outriggers continue the run of their beams to leeward to give a base for lee shrouds, mainsheet tracks and also to hang safety amas.

    I've been inspired by your comments and links to info concerning wand adjusted t-foils as well as canted t-foils.
     
  6. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    And you're right the two rudder foils would have to be of equal area and be an equal distance from the COG; both the athwartship and fore and aft distance.

    I was thinking of rudders that would both swing on a horizontal axis (thus allowing for kick-up and adjustable raking) and fully rotate on a vertical axis (thus allowing a shunt with a-symmetrical foils).
     
  7. Doug Lord
    Joined: May 2009
    Posts: 16,653
    Likes: 322, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Thank you. Rotating the whole rudder sounds great but the complication would come in changing the foil angle of incidence BUT since you're rotating the whole thing you could use a flap and since you're using a flap you can use a wand for altitude control. However, there are still at least two problems: 1) the wand would have to rotate with the rudder/t-foil, 2) I'm not sure how to get pitch stability from two equally loaded foils. A bit of research might answer that or you could try e-mailing Tom. Does the crew stay on the main hull or the ama? Does the crew move during a shunt? I'll look around and see what I can find.
    -----
     
  8. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    Doug, when you say flap, do you mean the horizontal elevator of the t-foil, or are you talking about trim-tabs on the trailing edge of the vertical foil ?

    I saw on one link you provided on another thread where the pitch was controlled by a wand that simply raked the whole t-foil back and forth thus changing the elevators angle of attack without the horizontal elevator needing independent movement.

    Yeah, the wand would have to rotate along with the whole foil.

    And having a 50/50 load on two foils that also have to provide effective and easy helm as rudders is another question i'm curious about.

    What i'm going to build is a day-sailing or at most camp-cruising proto-type where my position will start on the main hull but i'll move out to the ama when the extra righting moment is necessary.

    The boat's to be used in the semi-sheltered waters of the Puget Sound with occasional forays out past the Cape onto the deep blue.
     
  9. Timothy
    Joined: Oct 2004
    Posts: 307
    Likes: 15, Points: 18, Legacy Rep: 202
    Location: canada

    Timothy Senior Member

    lately I have been fooling around with the concept . My thinking at this point is that the aft foil if angled to counter slight weather helm and slightly canted because of the boats heel would lift the stern. The forward foil would be rotated almost 180 degrees and canted close to 45 degrees lifting the bow to a greater degree as well as increasing RM. Because the foils rotate 180 degrees they must be of a conventional section and there fore will not be as effective as asymmetric C J L or up tip foils. Adjusting the relative cant of the two foils would alter the relative percentage of vertical lift and the CLR . With each shunt the CLR would move aft. This would make it easier to design for a balanced rig with the mast centred for and aft. Pitch would be regulated by the large portions of the vaka forward and aft of the foils in a manner similar to that employed by Banque Populaire. In my dreams the ama would always fly and the vaka skim across the surface. My concern is that the heavily loaded aft foil even though angled forward for balance will ventilate and prove incapable of trimming the boat. I have a 16 foot model I built to test my folding proa concept and next week I intend to fit it with foils as configured in the rendering but fixed for one direction. I will sail it down the beech on a beam reach and see how it goes.
     

    Attached Files:

  10. Doug Lord
    Joined: May 2009
    Posts: 16,653
    Likes: 322, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    It's really important if you move fore and aft everytime you shunt?
    The flap would be on the lifting foil and would be controlled by the wand. The wand would be easy to connect/move.
    Using a wand to move the whole foil has been done but I don't like it because if you hit something the whole shebang could be messed up and it takes a lot of control power to move the whole foil. Weeds would adversely affect control of the foil where that can't(almost impossible) happen with a flap + wand.
    I still haven't been able to come up with a system I like for two nearly equally loaded foils. If the crew could sit forward or aft of center, that might allow for a set up that would work for both directions in terms of pitch stability: one direction the foils would be a canard , the other conventional. This would require changes to the angle of incidence with every change in direction as well as rotating the foils. Getting complicated.
    One thing you could do once you have a good solution is build a model. The model will scale perfectly for weight and the position of the foils but not for foil section-no big deal. Position of the rig can be reliably determined as well. But the best idea would be to experiment on the full size boat.
     
  11. Doug Lord
    Joined: May 2009
    Posts: 16,653
    Likes: 322, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    ===================
    Sure looks interesting, Timothy-best of luck! I'm gona have to think about the configuration and see if I can understand it.
     
  12. cavalier mk2
    Joined: Mar 2010
    Posts: 2,121
    Likes: 54, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    It would seem simpler to use the conventional foil assist and have a banana foil and T foil near each end for the respective shunts rather than trying to rotate anything, that way function can be maximized . I'd think about skipping foils for the ama, given enough wind it will want to fly/skim, playing the sheet and moving the weight should give control. A bruce foil might be interesting but anything in the water also adds drag. For complexity looking at the old thread on bows where we went onto the replaceable nose tangent did give me a laugh as I realized they could be flip up sterns for a transom function on a proa- just add a deploying T foil rudders. It is a challenge to find the KISS in a proa, every added gadget is another way not to work, part of the fascination.
     
  13. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    You're saying use a banana foil amidships on the main hull to take the 80% lifting load, and only leave the aft t-foil rudder in the water to take the remaining 20%, and simply raise the forward rudder out of the water completely ?

    That way, no rotating of rudders is necessary, and no leeway resisting foil in the ama is necessary.

    That sounds like a good solution if i can keep the COE to CLR balance right.
     
  14. tspeer
    Joined: Feb 2002
    Posts: 2,276
    Likes: 249, Points: 63, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Bernard Smith's Aerohydrofoil concept is basically a proa with hydrofoils.
    [​IMG]

    The latest incarnation of the aerohydrofoil is Sailrocket, which goes pretty fast. It lacks the fore-aft symmetry necessary to sail on both tacks, though.
     

  15. cavalier mk2
    Joined: Mar 2010
    Posts: 2,121
    Likes: 54, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    "You're saying use a banana foil amidships on the main hull to take the 80% lifting load, and only leave the aft t-foil rudder in the water to take the remaining 20%, and simply raise the forward rudder out of the water completely ?"

    Pretty close....I'd use a dedicated banana foil for each shunt too so the lift and clr can be put in the optimum location, trying to get a foil to work optimally in both directions would be a compromise. A boat with dedicated foils optomised for each direction will be faster than the weight penalty.
     
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.