Rudder design question

Discussion in 'Boat Design' started by SeaBird, Sep 16, 2003.

  1. Chris Krumm
    Joined: Aug 2003
    Posts: 92
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    Location: St. Paul, MN

    Chris Krumm Junior Member

    Understanding Aircraft Composite Construction (Zeke Smith)
    http://www.aeronautpress.com/book1prev5.htm
    Sample chapters online. Easily accessible for non-engineers, just algebra. Good intro to foam/cpmposite fabrication techniques.

    Marine Composites Handbook (Eric Greene Associates)
    http://www.marinecomposites.com/
    Very thorough intro to composite design, engineering, fabrication methods. More geared toward engineers and industrial processes. Entire book online in PDF format, but it’s huge. If you like it, buy the paperback from him.

    COMPOSITE AIRCRAFT DESIGN. (NEW REVISED 2003 Issue) &
    HOW TO BUILD COMPOSITE AIRCRAFT
    Both by Martin Hollman @ Aircraft Designs, Inc.
    http://www.aircraftdesigns.com/
    I have an 11 year old copy of “Composite Aircraft Design.” Great resource and intro to composite design and fabrication techniques, accessible to homebuilder. Very applicable to boat construction, though boats aren’t mentioned. I want “HOW TO BUILD COMPOSITE AIRCRAFT” because he mentions showing how to build both using prepreg and vacuum bag methods (new school) as well as carved foam core with wet layups (old school).

    Graphlite Carbon Rod by Jim Marske
    http://www.continuo.com/marske/carbon/carbon.htm
    This site was mentioned in an earlier post. Tohbi, an image from the site for spar sections using graphlite follows. The site has more.
     

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  2. Chris Krumm
    Joined: Aug 2003
    Posts: 92
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    Location: St. Paul, MN

    Chris Krumm Junior Member

    Seabird -

    Not sure how you'd be modeling your rudder in CAD prior to developing the mesh for ANSYS, but I have a suggestion for a simple foil "protocol" that I know would be simple to develop as a theme and variation in any program that uses ACIS or Parasolids.

    Pick a foil x-section to delineate the outside edge/perimeter. Your foil consists of:

    1) solid core of one low density material (PVC foam or long grain softwood)
    2) unidirectional composite spar caps at the maximum chord thickness flush with each face of the foil (think 2 troughs routed into the core that are filled with uni-d fibers bonded with resin)
    3) +/- 45 degree biaxial cloth wrapping the entire foil for torsional strength.
    4) perhaps a couple extra strips of biaxial cloth at the leading and trailing edges for impact resistance. You'd need to remove the space for this material from the core

    This scenario pretty closely mirrors how a lot of rudders and daggerboards get scratchbuilt. Starting with an extrusion of the foil shape, you could do boolean subtracts and differences and end up with a solid modeled foil comprised of the 3 or 4 elements listed above. The foil could start with a rectangular planform which could be adjusted to a taper or an ellipse if you had time. Probably easiest to leave the foil geometry as a fixed template at first and vary the material properties of the elements in FEA runs. You could also play around with the constraints - whether the foil is mounted on gudgeons and pintles, or held in a rigid trunk like a daggerboard-style rudder, etc.

    Good luck on your Monday proposal deadline Sounds like a fun project.
     
  3. SeaBird
    Joined: Sep 2003
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    Location: Montreal

    SeaBird Junior Member

    Thanks for the links Chris.

    ANSYS converts AUTOCAD, Pro-Engineer and many more design softwares into it's own preface and then you can apply meshing. Or you can design the geometry straight in ANSYS (I think I'll do that).

    Seabird
     
  4. coozeman

    coozeman Guest

    Hey seabird,
    A friend of mine who is a yacht designer with Rodger Martin did pretty much the same project you did when he was an engineering student in college. I've taken a look at his paper, and it will probably be of some interest to you. He is a pretty friendly and open person, so I am sure he would be willing to provide you with a copy and discuss his findings with you. email me at: coozeman@hotmail.com if you want to get in touch.
     

  5. gggGuest

    gggGuest Guest

    I can't see flexibility being useful in a rudder because it would mean that the greatest deflection was at the surface where you are most likely to get problems with ventilation at high speed. Similarly the only application I could see for flexibility in a daggerboard would be to simulate a gybing board type effect, but again I doubt this would be useful in practice because deflection would increase with speed, whereas you probably want it to reduce.

    A worthwhile area for an FEA type process might be in the whole interaction of tiller/pintle/rudder blade loads. Failure in this area is much more common on quick boats than of the blade itself. Maybe too complex for three points though?

    This might do as a starting point if you wanted to look at that route.

    http://www.sailingsource.com/cherub/rudstock.htm
     
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