Reversing the fittings on the top mast section

Discussion in 'Laser Talk' started by oztayls, Jan 16, 2012.

  1. oztayls

    oztayls Member

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    My stop mast has become soft so I want to reverse the fittings. Should I keep the fore/aft orientation of the tube or reverse that as well?
     
  2. Sail_J6

    Sail_J6 New Member

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    There is a really good video about this from Rooster :) Link -
     
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  3. oztayls

    oztayls Member

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    Thanks, in Steve's video, I think he aligns the stressed side the same way. Is this the accepted practice?
     
  4. Sail_J6

    Sail_J6 New Member

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    I expect it is because Steve will have done many of these in his career :) It would also seem to be correct as it will be less likely to break if the stress goes the same way - Reversing the stress could make it brittle :)
     
  5. AlanD

    AlanD Former ISAF Laser Measurer

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    As a metallurgical engineer, I'd love to see any scientific or engineering explanation of this.
     
  6. oztayls

    oztayls Member

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    Good to see two metallurgical engineers sitting on the fence Alan! I asked a ME friend last night what his thoughts were and he shrugged his shoulders;). I think you could box this one with the so-called work hardening of our masts. What are your thoughts on that Alan, truth or folk-lore?

    In the interests of research, I think I'll reverse the orientation and put the old compression side facing forward. If it breaks, you'll all be the first to know :)
     
  7. Sail_J6

    Sail_J6 New Member

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    As a child, I was making an assumption. Also the word 'seem' suggests that I do not know the correct answer, but am making an assumption to try to help a fellow sailor :)
     
  8. AlanD

    AlanD Former ISAF Laser Measurer

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    In part covered this a few weeks ago (see below). But essentially I do not believe that from ordinary use, Laser masts work harden, there for lining up the rivet holes etc will have no impact on on the mechanical properties of the spars. You could put forward a very weak argument that a rivet head 305mm from the top of the mast might increase friction of the sail preventing the luff adjusting easy but considering the amount impact the cunningham has on a sail that high up, the friction impact would be neglible. So the only real impact of a rivet filling the old hole is cosmetic.

     
  9. Merrily

    Merrily Administrator Staff Member

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    Alan,
    Any idea why the instructions that came with my Vanguard Laser said to always line up the top mast rivet with the gooseneck? They really meant this as there were also red arrows on the masts pointing to where they should line up. I always thought it had something to do with work hardening, but you say it ain't say so, n'est pas?
     
  10. AlanD

    AlanD Former ISAF Laser Measurer

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    Yes, it's because the rivet / rivet hole are stress concentrators, which basically means that it a localised point that the forces are magnified at to the point where if the rivet facing the opposite way, the forces can potentially exceed the stength of the material which will result in the top section breaking. This is completely unrelated to work hardening and whats being discussed in the rest of this topic. :)
     
  11. stuck in the 80s

    stuck in the 80s Member

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    As much as I want to believe in whats being said, I cant help thinking about Uri Geller & his spoon bending.
     
  12. Merrily

    Merrily Administrator Staff Member

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    Thanks, Alan.
     
  13. AlanD

    AlanD Former ISAF Laser Measurer

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    There are a group of metal alloys called "shape memory". If you bend them (or straighten them in this case) below a certain temperature, when the temperature is raised above a certain point, they will return to their original shape. If you chose the right alloy, just holding them in you hand is sufficient to cause the metal to warm sufficiently to change shape. These alloys are used quite a bit in electronics, but Uri just uses slight of hand.
     
  14. oztayls

    oztayls Member

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    That is the best explanation I have come across Alan, and at least we all now have a basic picture of what is occurring at the molecular level when our masts bend. I missed that earlier post, so thanks for repeating it here. Great stuff!
     

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