Rudder Design

Discussion in 'Boat Design' started by Norman Brown, Jul 11, 2009.

  1. MikeJohns
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    MikeJohns Senior Member

    I was just showing the mechanism of the trailing edge articulation directed into the flow for interest. They are definately not improving laminar just directing thrust.

    Sorry for any confusion.
  2. apex1

    apex1 Guest

    Nono RW, in this case you´re wrong, those rudders ARE articulated rudders! Of course not designed to improve laminar flow, just to improve maneuverability.

  3. rwatson
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    rwatson Senior Member

    I understand what you mean Apex - they have a bendy bit, so they are 'articulated', true.

    In my limited experience, the term 'articulated rudder' was used on the Americas cup articles, which was associated with the rudder trying to increase laminar flow. I was using the term in that context.

    Thanks for the clarification Mike, I was a bit thrown at first, so maybe others might have got the wrong end of the stick too.

    Any news from our prime articulator ?
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  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    remember that the boat does not continue on the same heading when the rudder is turned unless it stalls. The rudder develops lateral lift and rotates the boat, so the water at the rudder LE is now flowing at an angle to the axis of the boat. This is especially true of a sailboat with separate high aspect ratio fin keel and rudder. It would be less true of a sailboat with a rudder attached to a skeg or the aft edge of a low aspect ratio or full-length keel, but that would not be a high-performance boat anyway.

    About the best you could do would be a pivoted (not hinged) rudder that could change its profile as it rotated, taking advantage of the greater lift/drag ratio of asymmetrical profiles and high angles of attack, but the gain would be minimal and only apparent when turning hard.
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  5. Norman Brown
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    Norman Brown Junior Member

    In my case it is stern hung rudders, slightly canted for the heal of the yacht.
    Of course the problem of keaping the lamina flow at dif. speeds is difficult. However I think I have the outline of a solution in my (Small) brain. By spliting the rudder verticaly into 5 pieces and allowing up to 5' movement at each hinge point and controling this movement with rubber buffers (more movement at higher loads, less at low loads). I think it can be done. I will sketch something out in the next few days and post it in.
  6. rwatson
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    rwatson Senior Member

  7. Norman Brown
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    Norman Brown Junior Member

    Very, very interesting. Control of the flow and pressure in this way would save angling the rudders forward. Hence lower loads, but similar flow paths !
    Is it possible that a version of this has been done for many years already on ships hulls by placing a bulge on the base of the bow ???
  8. 30' SISU
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    30' SISU New Member

    Rudder design VS Hydraulic steering slip 30' SISU Downeast

    Condition: Keep needing to turn wheel to port, more so with more power.
    Vessel: 30' SISU with Fiberglass rudder and trim tab on port side rear edge of rudder.

    The vertical trim tap is screwed into the trailing edge on the rudder's port side. Also note we have a RH prop.

    Question: Does the Sea Star Hydraulic steering have a relief valve if to much pressure is exerted, or can I possible have an internal leak which due to the trim tab causes me to keep turning to port while underway.

    I've been upgrading this boat since I bought it a year and half ago doing repairs and upgrades ever since.
    It currently has a Cat 3116 300 Hp eng.
    My thoughts are that the original power had a LH rotation and the trim tab worked to neutralize the torque, but since the re power the running gear is now RH and the tab on the port side along with the prop wash is exerting to much pressure on the hydraulic steering.

    My plans are to replace this rudder with a Buck Algonquin Skegg rudder next layup.

    Any thoughts ???

    F/V Irian
  9. Gilbert
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    Gilbert Senior Member

    One thing that annoys me when the subject of rudders shows up in discussions is that folks talk like all rudders should be foils and you need to have read every book on hydrodynamics, aerodynamics, laminar flow and now even vorticity to even talk about them. Rudders operating in prop wash and rudders operating in no prop wash are in completely different situations and we shouldn't pretend that they aren't and it should be made clear at the outset what the rudder application will be. Rudders for high speed power boats are often wedge shaped in plan form with the trailing edge deliberately vented to the atmosphere. How different is that from your naca foil theory?
  10. CDK
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    CDK retired engineer

    No, rudders need not be foils.
    Mine were foils from GRP, but proved to be too small, so I replaced them with simple stainless steel plates with 50% more surface. Corners rounded off so you can touch them without immediate bloodshed, but nothing else. And not in the wash, but on both sides of the props.
    And except this one time when a mooring line hooked behind one and bent it, they behave absolutely the way a rudder should. I painted them with a special and expensive anti-fouling from "Epiphanes" for props and rudders, which was a complete waste of money, so now I regularly can be observed behind my boat with a piece of course 3M sandpaper. I'll keep on doing that until somebody comes up with a better suggestion.

  11. DUCRUY Jacques
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    DUCRUY Jacques Junior Member

    And The Trim Tab Vane Gear ?


    I am sorry if I am in late, but I have a question about the use of the trim tab for a selfsteering vane gear.

    On said usually that the first applications are the gear of Ian Major and blondie Hasler in the years 1950.

    But it seems to me that the French singlehanded Marin-Marie knowed already the principle of the trim tab for a autopilot : it-is true in your opinion ?

    If not, who is the inventor of trim tab vane gear

    Thank you by advance

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