Rudder Research?

Discussion in 'Boat Design' started by Simes, Oct 1, 2010.

  1. Simes
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    Simes Junior Member

    Hello Folks,

    Our 45' Schooner needs a new more efficient rudder. I am well aware that there are a lot of variables in the design and construction of a rudder. However this is something that I really want to do my-self.
    Firstly I am not a boat builder, just a man and his wife who are approaching the end of a 6 year refit of an old Schooner.

    Questions and Statements:

    Talisman is 45 foot LOD and 52' LOS, draws 8 1/2 feet and has a beam of 14 feet. Weighs around 26 tons. Is gaff rigged on both.

    We are changing the rudder because we are going to fit an Aries Wind Vane steering gear and the existing rudder is a "barn door". It has no balance nor leading edge. Is only supported at the foot and at the top (Just below the tiller). The rudder is Transom hung. There will be a scollop in the leading edge to allow for the prop'.

    Talisman is a full keel sail boat with a very pleasing shape, nicely faired and easily driven. Her transom is raked forward (going from deck to keel) by around 20 degrees.

    Talisman sails around 5 to 7 knots and maxes out around 9. 5 knots under power. Hard on the wind we are we tack through 110 degrees.

    So I think that I need a rudder that will give good lift at low speeds, will have a high stall angle, will have a balance that will allow the Aries to drive it. It should also look elegant

    How do I decide on the best foil shape?
    What are the best books to read (as a beginner to this)?
    Is there a data base of foil shapes with descriptions that I can just choose from?

    Thanks in advance folks,

    Simes
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    At these speeds I wouldn't worry too much. A simple spade rudder will do the job. Neat, simple and no fuss.

    You can spend hours and lots of money trying to refine a nice NACA shape and getting the exact CoE of the rudder and maximising the lift etc....but you wont make the difference in performance from a simple spade rudder to a "high tech" one go...WOW...you would hardly notice any difference on your boat. Im sure some would disagree, but the difference would need to be be measured by high tech equipment sensitive to small changes, not by many minutes in a simple race off the Spithead!

    Choice is yours, but i wouldn't bust a gut of it....just copy the basic size and shape from those around you.

    How is the weather on the IoW...getting chilly?
     
  3. PAR
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    PAR Yacht Designer/Builder

    Ad Hoc is right. On your boat a flat sided foil with fairly blunt leading edges and tapered trailing edges will do just fine. You don't need to go crazy. It would be helpful if you could post a picture of the current arrangement. A full keel boat isn't going to improve much with rudder changes. She'll be what she is.
     
  4. Simes
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    Simes Junior Member

    Ad Hoc,

    Not chilly as such but today it is blowing hard and wet, SW F8.
    I hear what you say about ultimate performance and I am not really bothered about that.
    Just that if I am going to build a new rudder (ultimately I do need some balance in this equation) then I want something a bit sexier. Lighter on the tiller, crisper in the tacks, cleaner on the straight and narrow rhumb line.

    Attached are a couple of Pix.

    Thanks

    Simes
     

    Attached Files:

    Last edited: Oct 1, 2010
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Is that down the far end of Artic road in Cowes? :)

    For balance, just aim for 1/4 chord, and you'll be ok.
     
  6. Simes
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    Simes Junior Member

    Good Guess

    But wrong, it is at the end of Kingston Road East Cowes, Kingston Marine Services. A trading arm of Cowes Harbor Commissioners.

    Any suggestions on an aero-foil shape to use?

    I want to build this rudder, I want to make it as good as I can.
    Any suggestions on which books or articles / web sites I should read?

    Simes
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Simes

    Bugger, it has been a while since i was in East Cowes!!!...is it near that "new" restuarant that over looks the Medina, at the end of a cul-de-sac....can't remember the name.

    As PAR noted above, a simple foil, basic and symmetrical will do. Nowt fancy required at all. Just place the stock 1/4 from the leading edge. Use the same amount of area that you currently have, if your current rudder has a decent enough rate of turn.
     
  8. PAR
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    PAR Yacht Designer/Builder

    This is a flat sided foil. The leading edge is a cylindrical section, the trailing edge is tapered at the 2/3's point, the shaft or axis for the balance is at 25%. Notice the trailing edge is squared off and left "crisp". This is intentional and desirable.

    Personally, I'd not use so much balance, unless you can insure a fair bit of separation behind that deadwood assembly.
     

    Attached Files:

  9. peter radclyffe
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    peter radclyffe Senior Member

    who designed this boat,Alden ?, you need to close that gap to the hull, bring the rudder as far fwd as poss, read skenes or chappelles, philips-birt
     
  10. Simes
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    Simes Junior Member

    Designer - Not Known

    Thought by those whom know that He was probably N American.

    The rudder is a ruddy nightmare, it stalls early, 20 deg'. Is heavy, no balance, .

    So if I go with your suggestions, 15% lead, little aerofoil shape and a squared off training edge.
    Then can I (or should I?) align the shape with the surface of the water or with the leading edge of the rudder? the two differing by some 20 deg'.

    Simes
     
  11. yipster
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    yipster designer

  12. TeddyDiver
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    TeddyDiver Gollywobbler

  13. gonzo
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    gonzo Senior Member

  14. peter radclyffe
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    peter radclyffe Senior Member

    it may be a good idea to check those bearings, as the design looks dodgy, if i may be impertinent
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    No, 1/4chord, or 25% (which ever way you prefer),... not 15%.

    Don't follow???:confused: (..or it's too early in the morning for me, I haven't woken up yet)

    Agree with the above too...those bearings:eek:
     
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