Just a simple question

Discussion in 'Boatbuilding' started by Skua, Aug 21, 2013.

  1. Skua
    Joined: Apr 2013
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    Skua Senior Member

    Is a 2x4 of solid wood, stronger than a 2x4 made of plywood? I have asked this question of several "pros" from carpenters to engineers, and gotten different asnswers. Figured I would ask those who's experience, matches my intended uses.
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    What are your intended uses ? Can't imagine too many applications where a solid piece of 4x2 would not be the choice.
     
  3. FMS
    Joined: Jul 2011
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    FMS Senior Member

    Stronger depends on what application.
    Plywood has many layers with alternating grain direction. This gives it strength in both x and y directions and dimensional stability with the trade-off of less strength in a single primary direction.
     
  4. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    There is no such thing as a standard 2 x 4

    What timber, how clear, how uniform is the grain ?

    In 80% of cases, laminated timber is stronger than solid wood.

    The term 'strength' is not even clear. You have

    Tensile - how hard to pull it apart
    Shear - how hard to snap it under a heavy weight
    Compressive - how easy is it to crush

    and a combination of these.

    However, for something like a keel, you have to to consider the working conditions. Generally, you would expect solid wood to last longer than plywood when its exposed to continual damp, especially when you have to let in slots for frames and other hull members.

    The 'intended use' mentioned by Mr E and FMS is all important.
     
  5. El_Guero

    El_Guero Previous Member

    Several have pointed out the obvious, it DEPENDS.

    2x4 made from two 2x2's is hard to beat. For the weight to strength solid wood is hard to beat. Especially at the price.

    But, in positions where the plywood is used for where it performs best, it hard to beat marine plywood. Say the skin for the hull, or decking.

    So, what do you intend to use this for?

    A keelson? Or, stringers? Go solid, or a larger piece from two smaller solid wood pieces. If for the skin on the hull? Go bs1088 plywood.

    If it will get wet, you must use solid wood covered, or marine plywood.
     
  6. dskira

    dskira Previous Member

    In the US the standard are 2 by 4 or 6 8 10 12
    Then 4 by 4 by 6, 8by
    And so on.
    The real measurement is 1.5" by 3.5" in the case of a 2by4 for example since it was considered that the customer pay for the rough dimension of the wood before milling. This is the reason why the dimensional number are these 1 by, 2by, 4by, 6by, 8by.
    It is a good wood from high end Douglas fir, even some red wood, PortOrford cedar, and even some of the oak can be find in dimensional.
    But also you can find house quality, spruce/hemlock/fir, of pine, all sort of pine.
    It is quite inexpensive, practical and without to much surprise. The price can be by linear feet.
    You find also the classical flintch sold by board foot of course.
     
  7. tunnels

    tunnels Previous Member

    If its bending solid wood is stronger !!! do you know why ?? :confused:
     
  8. Skua
    Joined: Apr 2013
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    Skua Senior Member

    Intended purpose is stringers. I have plenty of 2x8 2x6 1x6 dimensional in cedar, maple and fir. I also have 400 ft of 3/8, and 1/2 plywood (not Marine) A/A interior. All material will be epoxy coated first and then laid up with 1808 Triax.
     
  9. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    Do not use interior plywood on a boat build..................................
     
  10. Skua
    Joined: Apr 2013
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    Skua Senior Member

    It is completely dry now. Rear cabin bulkhead leaked for years before I owned it. All of the leaks and migration have been cured. If there is water in the bilge, I put it there.
     
  11. Skua
    Joined: Apr 2013
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    Location: Hunt's Pier WW NJ

    Skua Senior Member

    Boat is a 28 ft cabin cruiser Stringer on port side was compromised by water leak in bulkhead. Water migrated down nail holes in decking. The nails holding the cabin decking completely wasted allowing the deck to flop up and down. I am replacing the gas tank which developed a leak after 25 years, and decide to remodel the cabin.
     

  12. Petros
    Joined: Oct 2007
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    Petros Senior Member

    plywood has half the grain running in perpendicular direction, it is not suitable for loads in the primary dimension, and it will have half the compression strength in any direction as compared to compression loads in the axis of the grain. A clear solid swan timber is much stronger, and lighter too if the primary load is in the grain direction.

    Plywood is suitable where you have shear loads going in more than one direction, like the skin on the hull. And it would be stronger if you have compression in more than one direction on it. Plywood has more end grain exposed which makes it more prone to water intrusion unless all the edges are sealed well.

    A perfectly clear piece of straight grain lumber with no grain defects would be stronger than a laminated piece of wood with all the grain running the same direction (unlike plywood), because there are more grain boundaries cut in the layers. However, finding a perfect piece of wood is more difficult so laminating will be stronger since the grain defects tend to cancel, or be much smaller in a think vainer. You can also make curves and complex shapes without steam bending by laminating many thin layers.
     
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