Rudder Size vs Lee Helm

Discussion in 'Sailboats' started by ancient kayaker, Nov 7, 2013.

  1. BobBill
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    BobBill Senior Member

    Probably both. I figured first to go the Bruce way first, but then, after the AC, full foils.
    Then I thought about my penchant for simple and love of lollygagging (just sailing for its own sake) on occasion and pushed the phantasmagorical ideas out of my dreams.

    Simple, for me, includes being pragmatic-do what works if it works simply, not gratuitously.

    For example, Steve Clark once insisted that hard wings are the only venue for C cat racing. I immediately thought, while that may be true, it is also very impractical...as most things might be in the beginning, and that some sort of soft version might be possible...remembering the simple wings used on the fabric/stick aircraft of old...which offers the benefits of both worlds. (The narrow rig on the right above.)

    So, if I venture that far, it will be a soft air foil that is easy to tote and fly, rather than lift foils, which are, at least now, not simple, you get my drift. I have a ways to go, one hull is near finished, and the other is as well, but they remain separate and have to be joined and tested etc...the fun part. Then we try the crazier stuff, if it is simple.
     
  2. ancient kayaker
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    ancient kayaker aka Terry Haines

    The Bruce foil eliminates the need for the ama. I tried one a few years ago on my kayak, the foil and outrigger could be retracted and the sail came down similar to an umbrella. Although the sail was too small for upwind sailing it was fine on a reac or a run. The foil was very effective, completely cancelled any tendency to heel. Except, that is, for one memorable moment when I forgot to lock the outrigger before raising the sail and the outrigger folded itself up neatly against the side of the bow.

    Full lifting foils sounds like an interesting experience on an assymmetrical craft. Could take some experimenting to establish the foil location or - with foils on both hulls - the ratio of foil areas.


    Wicked thoughts section

    Problem with a hard sail is storing the thing aboard. I've always liked the idea of a folding, reefable fully battened soft sail with fixed camber, using the "Wright Brother's Flyer" wing type with fabric on one side to simplify raising and lowering sail, lightness and simplicity. Problem is the sail has to take wind on either side when tacking - I assume you have a tacking proa rather than the wind-on-one-side variety since you're contemplating foils. However, if you box ship like the classic proas, keeping the wind on the same side, there's potential for an interesting experiment. With such a wingsail using a symmetrical profile so the wind can play on it in either direction, the wing can be pivotted along its axis like the sails on The Maltese Falcon . . . :cool:

    I did a post on the idea here but never got to try it out due to prolonged illness during which my small home-built sailboat died of neglect :(
     
  3. BobBill
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    BobBill Senior Member

    Terry, This is what I have in my mushed mind...Imagine a narrow sail, tall and narrow (high aspect) that is more batten/sail than Dacron...see illus above.

    I figure the thing to be like wings on old bi-wing aircraft, but easily flexed to shape to tack...then, this is the maddening part, have Mylar or similar material that creates semi-turning or rotating leadd edge, when viewed from end, to give the right face to wind, like a wing on those old planes, but a bit fuller.

    As you note, full wings are not convenient...this thing would collapse like a Dacron soft sail, with some crew help and make it sort of normal.

    Of course, that may require a lead or forward and aft slot arrangement on a carbon stick (to keep weight down and make non-stayed rig practical).

    Like I said, later one, but I do think it can be done simply and easily, with some effort...and it might work on any boat, Sunfish to proa...

    And you are correct, boat is tacking outrigger (proa to some) but with sail that would be raised and lowered more or less conventionally, which is point of exercise for me.

    I just took the main hull up hill to back yard...for winter, and it snowed already.

    My winter work will be confined to getting akas (mold cradles to fit the 18 hull cradles) ready and planning deck on the outrigger that connects the akas to it.

    Holding off ordering ply for decks etc until spring...no point in having lumber set around...

    Also decided to add splash rail to port side of main hull and maybe the outrigger...not sure...everyday something comes up...love it.

    Boat will be able to sail, paddle or motor (2hp) I get it right.
     
  4. tspeer
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    tspeer Senior Member

    You have this backwards. To remedy lee helm, you want to move the sail area back and the CLA forward.

    Often the easiest way to move the sail area back is to rake the mast back.

    If you have a centerboard, putting the board down all the way will move the CLA forward. You could add a notch to the head of the board to allow it to angle forward a bit in order to move the CLA even farther forward.
     
  5. ancient kayaker
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    ancient kayaker aka Terry Haines

    Sounds good. Keep us informed of progress!
     
  6. ancient kayaker
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    ancient kayaker aka Terry Haines

    - oops. I have the same probem with left and right . . .
     
  7. SukiSolo
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    SukiSolo Senior Member

    Totally agree with T. Speer. You need to rake the mast or move it aft to get rid of lee helm. Mostly you can calculate the approx position and be only 10-20mm out at the foot maximum on a dinghy say up to 16'. The most extreme case I have cured was a National 12' where I had to cut away the foredeck and move the mast forward 55mm (over 2") along with slightly re-bracing it. In that case it was too much weather helm!.

    Most dinghies carry approx 30% of lateral area in the rudder +/- 7.5% so that gives you an idea. The only other thing that gives rise to unbalanced steering is too small a total lateral area. If you want to test this try sailing upwind with half centreboard! in a good boat. So sometimes total lateral area is important to steering.

    BTW in the middle 'sketch' it looks as if the dagger board(s) are a long way aft. Especially compared to the proa drawings which are much closer to craft I have seen which balance correctly. You always have the hard option of changing the dagger board position if it is a long way out.
     
  8. BobBill
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    BobBill Senior Member

    Tom Speer +1.

    And Terry.

    I kind of knew it was backwards but I also suspected Terry was like me, I suffer from light dyslexia and have learned to figure stuff out to compensate.

    Terry knows...as do you, and I thank you for the time to respond.

    In my case, cannot move the mast, so if the rig is not on, I will have to play with the dagger a bit or the yard hoist tension. The longer rudder will have to stay in closet.
     
  9. PAR
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    PAR Yacht Designer/Builder

    My mild dyslexia get me sometimes too. I pray to Dog every night that it might go away.
     
  10. ancient kayaker
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    ancient kayaker aka Terry Haines

    Send all prayers to me with a small fee and I will submit them to Dog. Best time is after she gets fed.

    That's why I like a sailing canoe - if you get lee helm you can always sail it backwards . . .
     
  11. Timothy
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    Timothy Senior Member

    Is this because the CE moves up and therefore further to leeward ( the opposite for appendages) ? If this is the case would the effect be as great on a multihull?
     
  12. Baltic Bandit

    Baltic Bandit Previous Member


    Well yes and no. its true that most rudders start losing their effective lift because off other factors when the boat heels. however as anyone who has raced a dinghy will attest to (and even boats like Olson 30s or J-24s), heel has a lot to do with steering forces. as crew on even a Star Boat, downwind ideally I as crew steer the boat and the skipper holds the helm neutral

    On a boat with a beamier hull shape like a J-24, one can (and I watched them do this to us) dramatically improve downwind boat speed by steering from the middle of the boat by having a crew member move laterally across the boat to steer the boat. 6" of 75kg crew weight shift will give you as much as 1 degree of turn.

    And this occurs because by heeling the boat, you create a force-couple between the now off-axis flotation vector and the CLR. Now it would theoretically be possible to design a hull such that you get more bouyancy increase in the stern than in the bow - but there are other reasons such a shape would be slow and so you don't see it.

    but in modern wedge shaped hulls you do see a reduction in RM in the bow area. That's in part why the Mini 650 that won the last MiniTransat was designed with a "scow bow"

    When heeled the immersed shape generates a fair amount of RM forward. This allows carrying of more foresail sail area in offwind configurations without sacrificing stability.

    And given the performance of that boat in this series, its seems that it wasn't just the skill of the pilot that got it done.
     
  13. MikeJohns
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    MikeJohns Senior Member

    I have to correct my prior post. It's around 6% shift in 'CLR' per 10 degrees of heel.
    But the rudder figure is correct with around 3 degrees of rudder to shift the 'CLR' by 10 degrees.

    These figures came from testing a variety of hullforms at the dept of NA at Osaka university. Thanks to AdHoc for getting the data for me from Prof Nomato.
     
  14. MikeJohns
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    MikeJohns Senior Member

    BB
    We could get into a tome on sailboat architecture here. Yes of course it depends on the craft. And a dinghy has a very high ratio of movable ballast, and in sheltered waters you will be able to steer effectively with weight shift (and hence heel control).

    The moment comes from the L_D vectors of the hull as a lifting body as well as the rigs relative vector contribution. The Lift/drag changes with heel as noted before.
     

  15. Manie B
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    Manie B Senior Member

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