comment on rudder

Discussion in 'Boat Design' started by lazeyjack, Sep 16, 2008.

  1. lazeyjack

    lazeyjack Guest

    according to a member, this rudder is from"the second best steel boat designer in world"
    IMO it is all very wrong,
    opinions from boffins please Also IMO the builder isvery capable and would benefit from working with a proper and qualified designer:)) as it is he is stuck in a slot
     

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  2. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Before the experts weigh in with real suggestions, I dont see a problem.

    Its obvious the boat needs a skeg with that size keel, so from a design point of view, and the performance point of view, it looks like a happy marriage to me.

    Were you suggesting just a stern hung rudder with no skeg, or what 'zacly ?

    Roll on the discussion.
     
  3. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    I'm just guessing, but it would seem if the front part of the rudder is fixed it would cancel out some of the actions of the movable part, create a resistance to sideways movement of the stern and make steering less responsive. It would also seem to add drag.
     
  4. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    yes - I understand your point. I do believe it increases drag, but probably less than having a full length keel would.

    From my limited understanding, I also understand the most efficient turning effect is achieved by using the flow around the outside if the "curve" as well. Having a flat plane in front of the movable surface can increase the "lift" in the direction of the stern, as well as the standard "action/reaction" effects of the rudder at an angle to the flow. Thats why rudders attached to vertical surfaces are always pinned as close to the keel or skeg as possible, so the "gap" wont destroy the laminar flow.

    Consider subsonic aeroplanes - their rudders pivot off the rear "lateral resistor" (tailplane) , and they go to a lot of trouble to use the induced lift to do their steering, before relying on the secondary high pressure effect, which creates a lot more drag.

    http://www.rudderpower.com/tech.html#stall

    is one site that discusses the benefits of maintaining the laminar flow around the rudder. They even put a third vertical plane on the rudder to increase the effect.

    I look forward to all the experts on the forum dropping some educated knowledge into the mix soon - even if it only sorts out my simplistic ideas.
     
  5. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Sometimes steel boat designers choose to make things very simple because steel boats are quite often built by non-professional boatbuilders. That might be the case with this design.
    It looks like a very simple and classic rudder design, created to limit the boat's draft. Notice that both the rudder/skeg and the keel are almost in line and that they have very low aspect-ratio. So they have been created for draft, not for performance.
    I do agree that should rudder/keel have been designed for VMG it would have a completely different look. :)
     
  6. diwebb
    Joined: Jun 2008
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    diwebb Senior Member

    Hi Lazyjack,
    in your opinion what exactly is wrong with the rudder??
    The boat appears to be designed as a cruising boat of moderate performance and relatively modest draft, and for that purpose the rudder appears to be more than adequate. The skeg will give protection from damage when accidentaly grounding and as R Watson has said the skeg should not really compromise performance.
    As with all boats the design is a compromise between performance, comfort and many other factors including personal preference. What were the original design intentions and does the boat and rudder meet these or not? That is really the question, and in my opinion there does not appear to be much, if anything, wrong with this design.

    David
     
  7. lazeyjack

    lazeyjack Guest

    hello!!

    there is very much wrong, i want to wait until the likes of t, speer come in, if you insist I will pm you,
    when one enters a design here, critism is ok, being rude or dirogatory is not, , unless one really asks for it:))

    David[/QUOTE]
     
  8. Manie B
    Joined: Sep 2006
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    Manie B Senior Member

    please clarify and make suggestions:?:

    i would also like to know what would be so much better for a cruising boat???:confused:
     
  9. Manie B
    Joined: Sep 2006
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    Manie B Senior Member

    this is a bit harsh dont you think??

    :confused: :confused: :confused:
     
  10. StrandedMariner
    Joined: Sep 2007
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    Location: Shanghai, China

    StrandedMariner Steelboatsailor

    [/QUOTE]

    I wholeheartedly agree with that. So is calling my personal preference for the rudder design of my cruising boat, and my reasons for having chosen it 'pure and absolute nonsence'.
     
  11. lazeyjack

    lazeyjack Guest

    \
    yes bit harsh but Wnyard said he was second best steel designer in world , so funny, there are 10000 ahead o f him, and wait and see abt rudder
     
  12. lazeyjack

    lazeyjack Guest

    I wholeheartedly agree with that. So is calling my personal preference for the rudder design of my cruising boat, and my reasons for having chosen it 'pure and absolute nonsence'.[/QUOTE]
    you didnot design it mate, ,
    trouble is you cant stand comment on your baby, calm, its ok my first boat had MUCH worse, but I learn the hard way, there are a few mech engineers turn to design, excellent folk, but I have altered many rudders built by such folk, one was a ships cap (real ship) and also dc8 pilot, a true frind of mine and brill engineer, who turned to design, made a rudder like that had to change it, the main fault is the bloody big gap between the rudder and hull
    i rang thsi Dix once, he was so stuck in a groove, wont listen to anything
    and to compare with say, farr, or dubois. or frers, all have wonderful steel boats up to 150 feet with guess what ,spades
    cheers
     
  13. StrandedMariner
    Joined: Sep 2007
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    Location: Shanghai, China

    StrandedMariner Steelboatsailor

    you didnot design it mate, ,
    trouble is you cant stand comment on your baby, calm, its ok my first boat had MUCH worse, but I learn the hard way, there are a few mech engineers turn to design, excellent folk, but I have altered many rudders built by such folk, one was a ships cap (real ship) and also dc8 pilot, a true frind of mine and brill engineer, who turned to design, made a rudder like that had to change it, the main fault is the bloody big gap between the rudder and hull
    i rang thsi Dix once, he was so stuck in a groove, wont listen to anything
    and to compare with say, farr, or dubois. or frers, all have wonderful steel boats up to 150 feet with guess what ,spades
    cheers[/QUOTE]

    I am happy with any comments, because my belief is that we keep learning all our lives. I also agree with you that for a racing boat there would be no other choice for me than a spade rudder.
    For a long distance cruiser however, I prefer the extra protection and directional stability of a skeg mounted or hybrid rudder. I will give up some performance that way, and I am aware of that. I don't think there is 'total right' or 'total wrong' in any design. We will always have to find a compromise between pro's and cons, based on what purpose we want to use a boat for.

    Cheers,
    Andreas
     
  14. lazeyjack

    lazeyjack Guest

    Andreas
    thanks for taking it in thew spirit it was intended
    BUT most modern cruisers and I mean cruisers in the Coral, use spades
    Big advantages with a proper rudder
    are
    less work for pilot and believe me, a pilot continually working drives you nuts

    very good easy helming, with lightness of helm, and once again that rudder in a strong reaching blow will test the patience of a strong man and will more than likely drive your lady from the helm

    I am no hydrostatics eng, but all the rudders I have tested with gaps like that have made life difficult
    it is all to do with the pressure on back,the water flow over the top, that is why you see such close fit on good boats , that is why i believe thsi guy is not a qual navel arch, but one who turned to it later? that is why I wanted input from Tom and other experts
    how much balence does it have, ?
    oh SORRY to members that picis tiny vs of one in Wyhs getting there 43, you cant see it properly here
     

  15. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    I dont get all the points you raise here LJ, and maybe the picture doesnt show what it is you are trying to say.

    The only thing that did "click" was a hint about the effort of turning the thing. Are you saying that because it is not centrally pivoting that the effort in operating it is excessive?
     
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