Thistle Class Rudder

Discussion in 'Fiberglass and Composite Boat Building' started by 10Hydro, Sep 8, 2008.

  1. 10Hydro
    Joined: Sep 2008
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    Location: birmingham

    10Hydro New Member

    While I've read many post on this forum for quite some time I am a new to posting. I have built molds and I am familiar with many lay-up techniques including vacuum bagging and resin infusion. My molded parts have typically been in 1/2s and bonded/taped together. My question is how is the best way to mold and lay-up a thin foil shaped rudder for a Thistle Class? I can mold each 1/2 separately but am unsure of how to lay-up. With it being so thin from 3/4"to 7/8" it seems too thin to lay-up in halfs and bond together. However, I'm not sure how to lay-up with matched molds without having any voids inside. I really want to mold both faces as opposed to overlaying over a core, but am open to suggestions. Thanks for your input.
     
  2. alan white
    Joined: Mar 2007
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    alan white Senior Member

    Just a suggestion. Such a thin rudder will be difficult to mold unless you make it from (heavy) solid glass/polyester (or somewhat fragile if you attempt to core it).
    Why not make it from a few layers of thin plywood sheathed in glass/epoxy?

    Alan
     
  3. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Unless you have the moulds already made, building and fairing a rudder like alan suggests is going to be less work.

    I would tend to go for some light but strong wood rather than plywood myself (the local wood shop can advise) , because shaping plywood with its multiple laminations is a bit of a bugger.

    You can even pre-cut vertical sections to shape and laminate them for extra strength and efficiency. Cover with epoxy and cloth for strength.

    If you do a good enough job, it can be a plug for a master mould if you want to do others.

    I see the rules dont specify rudder size, weight etc, so using the wood technique you could build a few shapes for experimenting - perhaps have a few for different racing conditions.
     
  4. Phil Locker
    Joined: Oct 2004
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    Location: Ottawa, ON, Canada

    Phil Locker Junior Member

    Thistle rules are in fact fairly restrictive on the rudder. They have to be within tolerances for both planform and thickness. And they also have a minimum weight to meet.

    We CNC our thistle cores from strip laminated Douglas Fir, and have a proven fast shape. Why not just contact us to mill a core for you, then you take it from there with 'glassing and fairing?

    Cheers
    Phil
     
  5. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Thats interesting Phil - I couldnt see any reference to the rudder in the class specs I found on the internet.

    Do you have a better link?

    Your CNC suggestion is the go - viva la computadora
     

  6. Phil Locker
    Joined: Oct 2004
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    Location: Ottawa, ON, Canada

    Phil Locker Junior Member

    Thistle rudder specs

    No link, sorry. I've just got a really bad scan of the appropriate page of the "Official Thistle Class Rules" that you have to look squinty-eyed at to make out the numbers. (given by the customer that first ordered one from me).
     
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