Foam core dodger/arch construction

Discussion in 'Fiberglass and Composite Boat Building' started by SwedenYachtsDaniel, Oct 1, 2019.

  1. SwedenYachtsDaniel
    Joined: May 2018
    Posts: 10
    Likes: 0, Points: 1
    Location: Norway

    SwedenYachtsDaniel Junior Member

    Hello

    Im planning to build a hard dodger for my Sweden yachts 38 as shown in the pictures from SketchUp. (im new to Scetch up) , I might change som things a little bit , but all in all it will be close to the pictures i added. 1m headroom, 2m wide and 1,5m long.

    Here is what i am thinking of:
    I want to use epoxy as resin.
    I would like to use 450g biaxial glass. (I already have a lot of that)
    I want to build it out of a foam core, maybe plywood core for the integrated "targa" arch, ore what ever you would call it
    The targa that is thicker in the picture is about 200-250mm wide and is where the maincheet will be attached. Thats about 75% of the boom length from the mast

    It should be strong enough to stand on if needed
    Strong enough for the maincheet

    My questions are:
    What density and thickness of foam core do you recommend for the dodger and arch ? And how many layers of 450 biaxial or other glass do you recommend ?

    Any thoughts are welcome .
     

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  2. Stingrig
    Joined: Apr 2019
    Posts: 6
    Likes: 0, Points: 1
    Location: Netherlands

    Stingrig Junior Member


    My questions are:
    What density and thickness of foam core do you recommend for the dodger and arch ? And how many layers of 450 biaxial or other glass do you recommend ?

    Any thoughts are welcome .


    Hi,
    For a similar project I used 20 mm thick 60 kg/m3 Corecell foam and 1200 g/m2 biaxial glass: Doghouse / cabin top – DIY boat building Doghouse / cabin top – DIY boat building http://www.karelvanbrederode.nl/uncategorized/doghouse-cabin-top/
    60 kg/m3 is very light. 80 - 100 kg/m3 is better and won't add much extra weight.

    The mainsheet will put a big load on the dodger. Do you intend to spread the load by using a rail system?

    I have stiffened the aft edge of my dodger by using extra unidirectional glass (solid laminate, removed the foam) but I will not attach my mainsheet there!

    Regards,
    Stingrig
     
  3. Chuck Losness
    Joined: Apr 2008
    Posts: 311
    Likes: 37, Points: 28, Legacy Rep: 135
    Location: Central CA

    Chuck Losness Senior Member

    If the designer of the yacht is available you should contact him or her to design your dodger. If not you will need to have the dodger designed by a NA with a strong structural engineering background. The forces from the mainsheet can be quite large especially from an accidental jibe in strong winds.

    I have used SketchUp for years. It has a few quirks. If you don't have SketchUp for Dummies get a copy. It might be available online for free. It will really help you get up to speed. I still consult mine.

    Have fun with your project.
     
  4. SwedenYachtsDaniel
    Joined: May 2018
    Posts: 10
    Likes: 0, Points: 1
    Location: Norway

    SwedenYachtsDaniel Junior Member

    Thanks for your information. I was thinking about 80kg 10mm foam for the dodger, whit areas and some stripes of double 10mm due to windows and as "stringers"
    Yes , I will have a 1-1,5m long rail. So the load wont be on a singel point.
     
  5. SwedenYachtsDaniel
    Joined: May 2018
    Posts: 10
    Likes: 0, Points: 1
    Location: Norway

    SwedenYachtsDaniel Junior Member

    Thanks
    Thanks for the tips about SketchUP for Dummies.
    The designer Peter Norlin died 2012 , r.i.p
     
  6. Stingrig
    Joined: Apr 2019
    Posts: 6
    Likes: 0, Points: 1
    Location: Netherlands

    Stingrig Junior Member

    Have you considered using your existing sprayhood frame (if you currently have a sprayhood) to build your hard dodger? Different look but much easier to build than the design you posted. Here's an example:

    buiskap-nat-dak-375x500.jpg

    This small one was built with 15 mm PVC foam. I don't remember the specs of the laminate.
     
  7. Blueknarr
    Joined: Aug 2017
    Posts: 730
    Likes: 129, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    Swedish Yachts Daniel,
    Go directly to a reputable NA. Do not pass go. Do not collect $200.00.
    Three very important engineering questions to answer.
    1 How to make dodger strong enough to sufficiently resist main sheet loads? So dodger isn't torn apart.
    2 How to sufficiently attach dodger to cabin top? So dodger isn't torn away from cabin.
    3 Is cabin top strong enough to resist sheet loads with the added leverage from dodger? So cabin top isn't ripped away!!

    It is pointless to continue until the third question is answered.
     

  8. TeddyDiver
    Joined: Dec 2007
    Posts: 2,565
    Likes: 113, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Was there a traveller before, about where the dogger/targa ends? Adding a structural partial bulkheads or partners on both sides to spread or tranfer the mainsheet loads where the traveler was helps much with the engineering..
     
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