Bending wood over steel frames..?

Discussion in 'Sailboats' started by Omeron, Jun 7, 2007.

  1. Omeron
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    Omeron Senior Member

    These are the pictures from 'spirit yachts' web site.
    Always wondered,how such two very different materials, with different
    mechanical properties, can be married to form a load bearing structure.
    This is not even a static structure, like a building,where you would expect the steel to carry the load, and wood to cover it up.
    Here, i guess, the wood frames are load bearing, and the steel is providing additional strength and stiffness near the keel area.
    So both of them are required to play their part.
    What happens when the entire hull flexes,when temparatures go high and low, when humidity changes,or after a million time of cyclic loads.
    As an engineer, i was thought, not to mix and blend two different materials,
    as eventually, they would work themselves out and start to behave independently of each other with drastic results.
    Well, may be, that was a long time ago, perhaps materials now go through
    marriage counseling, before they are used!
     

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  2. nero
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    nero Senior Member

    http://www.ledonduvent.com/

    This ship was built in Germany in 1940. It is steel/iron frames, wood keel, and wood planking bolted on. She is quite tight and has no leaks in the hull.

    When she is hauled out for bottom work and then put back in all the planking seams move a bit. Just enough to crack the paint.
     
  3. jehardiman
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    jehardiman Senior Member

    You need to get a good book on how ship structures work and the loads that they are subjected to. You really need to understand the different nature and requirements of a free floating body subjected to primary (girder), secondary (frame), and teriary (shell) loads. A civil or mechanical engineering background poorly prepares you for analyizing ship structures, (I know, I've had to educate a few in my time). In the picture you show, the wood is to hold the planking and the steel is to hold the shape. The hull is supported as flexible open shell with sectional properties maintained by the more ridgid frames. They are using the materials correctly.
     
  4. la cage
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    la cage Junior Member

    The moisture content of the wood, in the contact area between the steel and the wood will always create a problem wheather internally or externally. The steel mesh that I use with a variety of materials has not been a problem, because the steel is incased in a closed cell foam before fibreglassing.
    www.bourneboats.com.au
     
  5. MikeJohns
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    MikeJohns Senior Member

    The frames are stainless steel. I hope they have carefully considered their SN curves.

    Composite ships, Iron frames with wooden planking were used a lot before ships moved to metal plating.

    Cage
    Although modern bedding sealants have significantly diminished this problem and in this application they would stop all problems WRT trapped moisture.

    By the way your construction technique is certainly novel and a discussion of it is worthy of a new thread.
     
  6. la cage
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    la cage Junior Member

  7. Pierre R
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    Pierre R Senior Member

    surprisingly steel and many hardwoods have vary similar expansion properties. The wood also has some give and will accomodate in all the right places. I see no problems with this type of construction.

    I would have a concern with the quality of stainless used as the stainless would be subject to crevice crack corrosion between the wood and the stainless in the presence of standing water.
     
  8. Paul Scott
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    Paul Scott Senior Member

    fwiw, Steve Rander's 'Rage' was done with a steel frame, c.o.v.e system- e glass, cedar, eglass, klegecell, e glass, cedar, e glass. West System, e glass and wood used unidirectionally. Rage has been raced a lot for a decade or so- it's so light and fast that it gets airborne off of waves (I asked Steve what it was like when he landed, and he said it was like a garbage truck landing on a house). They put Rage on a sand bar at 11K, got off and continued racing.
    Google Schooner Creek Boat Works, and you'll find info on her. She was banned from the transPac for years.

    Paul
     
  9. Omeron
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    Omeron Senior Member

    Pierre R, wouldnt it make sense to coat steel with some suitable
    material, and make it waterproof before bending the wood over it?
    Since it is not going to be submerged in water, any decent paint,
    epoxy etc, could cope with precipitation, humidity etc.
    But i guess the bore holes would still be problem areas.
     
  10. MMNet SEA
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    MMNet SEA Junior Member

    Looking at the pictures - it appears that the metal frames are only there to provide the correct bend to the laminated wood frame during the lamination process. The metal frame patterns remain in the builders yard ????
     
  11. jehardiman
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    jehardiman Senior Member

    No, those are ring frames, not moulds, otherwise there wouldn't be camber in the "deck" and all the expensive lightening cutouts.
     
  12. MMNet SEA
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    MMNet SEA Junior Member

    unfortunately the picture's scale gave me the impression that the distance between the top and bottom of the ring frames would be inadequate for internal cabins etc. I guess I was misled by the size of one of the clamps.
    Thanks
     
  13. Omeron
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    Omeron Senior Member

    This is an impressive boat by 'Spirit' Yacht.
    If you browse their site, you will see the entire boat, and the permanantly
    installed ring frames.
     
  14. MMNet SEA
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    MMNet SEA Junior Member

    Omeron can you give the full URL? - the one that shows the ring frames.
    I could not find the specific one.
     

  15. Omeron
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    Omeron Senior Member

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