building materials

Discussion in 'Boat Design' started by adriano, Jan 17, 2013.

  1. adriano
    Joined: Aug 2009
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    adriano Junior Member

    Hi there,
    could anybody confirm whether for a motor launch hull (outborder) of 19 ft over all, approx 350 kg displacement following material/thikness are acceptable?:
    wood/epoxy construction
    first layer: 10 mm. Red Cedar - epoxy/ stripplanking
    Second layer: Red Ceder 4 mm. only 1 diagonal plank - epoxy /cold molding
    (total wood thikness 14 mm.)
    bottom: 2 layers 300gr.sq.mt. biaxial fiberglass cloth
    top: 1 layer 300gr. sq.mt. biaxial fiberglass cloth.
    Appreciate any comments/suggestions thanks
    Adriano;)
     
  2. alan white
    Joined: Mar 2007
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    alan white Senior Member

    That sounds very beefy. Your displacement calls for a light hull with a low carrying capacity. Are you sure your displacement figure isn't actually your carrying capacity?
     
  3. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Hmm..350kg weight.

    Its light. I built a 20ft outboard skiff, plywood and eglass, 40hp outboard at 400kg. perhaps a bit more

    The hull ply was 9mm, eglass biaxial skins were 400gr. inside and outside with some local reinforment ...frames every 750mm , two full length longitudinal and a 12mm ply deck. Its pretty strong.
     
  4. adriano
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    adriano Junior Member

    well.. that's the dream target for the moment, it's not final.
    adriano
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Adriano, good to see your post. One of the very first things you need to do in a design, is to work out the weights of stuff. We call this the center of masses calculations and if done by hand, quite tedious, but very necessary if you expect the boat to float and trim anywhere close to what you want. Anything less is just a guess and these usually don't work out well without decades of design experience to rely on.

    Why bother with the multiple lamination of cedar? Just strip plank to the thickness you need (14 mm) and save yourself some effort. Your sheathing schedule sounds modest, unless there's some internal framing for additional support.
     
  6. adriano
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    adriano Junior Member

    Thanks Paul,
    some minimal framing in the bilge area and a couple of longitudinal battens are expected. Actually it's a friend's project and not matter of high speed boat I am also little skeptical about the weight of course and I am trying to find out first the minimum hull weight per sq.mt.. Anyhow the 4 mm. cedar planks is to have additional wood strength diagonally, further it should be vernish and give a modern look to the external layer of a wooden hull . Once you add biaxial glass cloth 3or400gr. this should be ok?! I do not think there are other ways left (in this case) to save weight on the hull eccept carbon fiber is used which would increase the costfacor toomuch.
    Plywood is being excluded for different reasons!
    I do not think we can use strips smaller than 10 mm.wide for technical reasons and to use wood veneer 3 mm.planks is a problem at moment because of availability or higher costs to get it.
    Adriano
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Veneers over the strip planking would be the lighter and stronger choice, though I understand your availability problems. Veneers can be ship via UPS, so this might be an option. Biax will provide a lot of cross grain strength, so you could skip the diagonal layer.

    It's really tough to offer scantlings, when you don't have a very good "picture" of the boat. I think you can use the light biax, but it's probable you'll also need a skin on the inside as well. A 300 cgm will work, though I still think this is light. Without a full set of dimensions and some ideas on weight, equipment, operational speeds, sea state conditions you'll ask it to endure, etc., most is just crude speculation and shouldn't be relied on.
     
  8. adriano
    Joined: Aug 2009
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    adriano Junior Member

    Hi Paul,
    I am trying to contact you, is yr e-mail address:
    paryachts@comcast.net
    still correct?
    Kindly let me know thanks
    Adriano;)
     
  9. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Adriano, if you visit my website you could download from it an application I have developed to calculate the scantlings of pleasure crafts according to ISO 12215-5. I believe this application will helps you.
     
  10. adriano
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    adriano Junior Member

    Thanks a lot Tansl,
    I'll do it and let you know.
    Adriano
     
  11. adriano
    Joined: Aug 2009
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    adriano Junior Member

    wind surf board

    Is anybody awere of building plans for an udated wind surf board?
    I would like to build it in cold molding since I have good access to red cedar 3 or 2 mm. veneer.
    Mast, boom and sail might be wise to buy ready made or in kit! anyone knows any source?
    I appreciate any help.
    Adriano;)
     
  12. adriano
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    adriano Junior Member

    Hi Transl,
    by the way, can you give me yr website address?
    Thanks
    Adriano
     
  13. TANSL
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    TANSL Senior Member

  14. philSweet
    Joined: May 2008
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    philSweet Senior Member

    adriano, I'd recommend you pick up Gerr's Boat Strength and work your way through it. You'd get a better feeling for how all the bits work together and the proper size relation for the various pieces that tend to produce sound and economical boats. If not Gerr's, then some other scantling rule, but Gerr's is well presented, cheap, widely available and provides basic cook-book recipes for small craft done is a range of materials.
     

  15. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    Do we understand that you intend that the topsides be varnished bright? Biaxial glass and a bright finish don't go together very well.
     
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