Help with designing a new rudder for a fisher 34 motorsailer

Discussion in 'Boat Design' started by dm567, Feb 10, 2012.

  1. dm567
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    dm567 Junior Member

    My 1985 fisher 34 motorsailor's rudder is getting old and was soaked with water on the last haul out. It has not delaminated, however. I dried it out and put a barrier coat on it but I'm considering a new rudder on my next haul out.

    I've found a picture of what is called a miracle rudder and was wondering if my local welder could put one together for me.

    My questions are:

    Can it be made entirely in Stainless? How?

    and

    How to shape the foil?

    rudderscompared.jpg

    The picture on the right is the miracle rudder.
     
  2. dm567
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    dm567 Junior Member

    picture of my rudder

    Fisher 34.jpg
     
  3. dm567
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    dm567 Junior Member

    oops- wrong picture

    Here is a picture of the rudder. The former is a picture of the entire boat; also with the rudder. Fisher rudder.jpg
     
  4. PAR
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    PAR Yacht Designer/Builder

    The Miracle rudder pictured will do fine at speeds over displacement, but not so much on your boat. You'd be best off with a 00 series foil or a flat sided foil. Both will preform well at the speeds you'll be moving at and under sail, they will not be nearly as draggy as the Miracle, which really isn't much of a miracle. The picture makes it hard to tell, but it appears you already have a slab sided (flat or straight sided) foil section on your current blade. If it's working well (I suspect it is, knowing the boat), the sectional shape shouldn't be "played" with. Make a new one using slab sided sections or step up to a 00 series, which will improve efficiency slightly.
     
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  5. daiquiri
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    daiquiri Engineering and Design

    Not every welder can do it. It takes a magic welder to get a miracle rudder. :p

    Apart that - your boat really looks gorgeous. :)
     
  6. daiquiri
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    daiquiri Engineering and Design

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  7. mydauphin
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    mydauphin Senior Member

    I forgot what things on the top and bottom are called they basically make rudder act bigger than it really is. The extra thickness at the back keeps it from stalling at a higher angle of attack. You can build anything out of stainless but consider yourself lucky if someone would do it for much under $800.
     
  8. michael pierzga
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    michael pierzga Senior Member

    Yah...I really like those Fishers. I see your miracle rudder with the end plates and flat trailing edge on many workboats but have no experience.
     
  9. FAST FRED
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    FAST FRED Senior Member

    Stainless UNDERWATER ?

    Much ungood.

    Google crevice corrosion.

    FF
     
  10. PAR
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    PAR Yacht Designer/Builder

    As long as it's a good grade of stainless and has a reasonable flow over it, the material works quite well underwater.
     
  11. michael pierzga
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    michael pierzga Senior Member

    If your a welder build of steel. Steel box rudders need to be sandblasted, epoxy primed , filled to displace water and anoded. Heavy and Lots of work

    Glass and foam over a webbed rudder stock is very easy to build and durable.

    Id duplicate your original rudder shape in foam glass ,then add the endplates. If the end plates prove undesirable simply grind them off next year.

    Google PHILS FOILS and he has a handy tutuial on building a composite rudder blade . Vacume bagging is a option...not needed.

    I have never seen endplates on a sailing boat.....motorboat yes
     
  12. PAR
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    PAR Yacht Designer/Builder

    End plates on that hull will be of no benefit, just drag, which the hull has plenty of anyway. A foam sandwich is a good idea as are other options, preferably ones with inert materials so you're not chasing issues constantly.
     
  13. viking north
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    viking north VINLAND

    Thats a straight forward rudder to weld or form and glass up. Also as PAR suggested no big deal to fabricate in a 00 series foil. Too bad your are so far away as these are the type of small jobs that i like to play around with now that i've basically shut down my operation but still have the shop and all it's tools for hobby.---Ya have to admit those Fishers are a nautical looking piece of gear.

    A yacht is not defined by the vessel but by the care and love of her owner--
     
  14. daiquiri
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    daiquiri Engineering and Design

    Hey Viking, how is your project proceeding?
     

  15. viking north
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    viking north VINLAND

    It's in stall mode right now for the next couple of months, I have it located in the unheated right bay of the shop with the keel base mold patially completed. I am taking a land yacht holiday down south (first in 3 yrs.) for the next 3 months but it's full bore full time ahead when i get back. It will be warm here then and I have all my ducks in a row(design (thanks to you guys)-materials-eqpt.paid helpers) so it should come together reasonably fast.(hate to say that as Murphy is always around the corner). I am really enjoying this build so all in all it should be a fun project. Thank you for the thoughtfullness of remembering and asking ---Cheers Geo.

    A yacht is not defined by the vessel but by the care and love of her owner---
     
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