Do spars deteriorate?

Discussion in 'Laser Talk' started by Rubicon, Aug 4, 2010.

  1. Rubicon

    Rubicon New Member

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    I'm looking at getting a new top section for my mast but have been offered the top section from a very old laser that has hardly been used in the last 5 to 10 years. Does it lose any flexibility or change in any way with age?
     
  2. 49208

    49208 Tentmaker

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    Flexiblilty - no

    You do want to check that it's straight.

    You do want to check to see if it's already been end for ended. If it hasn't, that's a plus and probably the first thing you want to do if you decide to get it.

    If it's already been end for ended, it's worth well less then 1/2 the cost of a new one
     
  3. Wavedancer

    Wavedancer Upside down? Staff Member

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    If the spar was put away wet, especially after a sea outing, I would be concerned about corrosion.
     
  4. urbo100

    urbo100 Ian

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    What is the reason behind end for ending the top section? Also wouldn't you be left with a rivet hole where the stop fitting was. What is the recommended way to do this?

    Ta Ian
     
  5. gouvernail

    gouvernail Active Member

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    Nah. Once they are teriorated they stay that way forever.
     
  6. AlanD

    AlanD Former ISAF Laser Measurer

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    From a metallurgical perspective, the mechanical properties of the spar will not change with age (unless stored at temperatures close of above the boiling point of water).

    The main issue is with corrosion around the rivet holes, particular the rivet on the collar as this is a high stress location. If there is any corrosion it would be a good idea to end for end the section.
     
  7. 49208

    49208 Tentmaker

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    The most common cause of breakage is at the rivet hole on the collar (max load from bending, corrosion, putting the rivet towards the front, etc) So, not knowing the history, swapping the ends lets you "start over" with a section that has not been subject to those stresses.

    Yes, you have a left over hole - but it's in a location near the top now that has very little stress, and you can simply cover it with tape
     
  8. laserxd

    laserxd Member

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    The aluminum is protected by a thin layer of aluminum oxide, for this reason the metal has good corrosion resistance.

    You should check that the spar is straight, shows no signs of corrosion, cracks ect (corrosion and cracks=time for a new spar). If the top mast is bent you can bend it back by placing it in the lower mast section, resting it between the ground and a solid elevated base, then apply smooth downward pressure until the bend is out.

    When you have to straigten the mast on a regular basis then its time for an end for end, or a new top mast section.
     
  9. Rubicon

    Rubicon New Member

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    Had a look at the spar on the weekend, it is straight but the collar (is that what it is called?) that the bottom section comes up against moves a bit with some slop in the rivets. Each plastic bit has been put on with 2 rivets, I'm starting to think it might be better with just one. This spar comes at the price of a beer so I'll take it, just need to work out how to make sure it will be OK to use.
    Regards.
     
  10. J22sailor

    J22sailor New Member

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    The timing on this thread is funny as I just broke my top section tonight in a breeze of about 15-20kts. The snap was the classic break right at the rivet and collar and I can only assume was due to deterioration on my 1996 Laser and original spars. Now the question is whether to purchase a Laser top section or a practice upper spar from APS or intensity. Any thoughts or personal observations on practice spars?

    Also, what is the general consenus on the placement rivet of the upper spar.....do u like it to face aft or forward when you are sailing? What is the best position to lessen the load on this weak spot?
     
  11. 49208

    49208 Tentmaker

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    You want the rivet facing aft.

    As far as practice vs class legal. The upper is standard extrusion, so they should have similar characteristics.

    (and you can turn your broken upper into a spare boom)
     
  12. AlanD

    AlanD Former ISAF Laser Measurer

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    Even if the dimensions are the same, it doesn't mean that the alloy composition or the heat treatment that gives the mechanical properties are the same.
     
  13. 49208

    49208 Tentmaker

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    Agreed - That's why I said similar, not same. (but I have deflected one and it fell within the range of others that I have numbers on)
     
  14. AlanD

    AlanD Former ISAF Laser Measurer

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    Deflection tests are related to the stiffness. But stiffness is dependent upon only the cross sectional area and the young’s modulus. The young’s modulus is within most aluminium alloys identical and not impacted by the heat treatment. Essentially as long as long as you remain within the alpha phase alloys (most commercial alloys) the number is the same.

    Alloy composition and heat treatment impacts on a range of mechanical properties including yield strength (when the material deforms permanently), UTS (when it fails because of the load), brittleness, hardness etc.

    Variations between top sections deflection will be identical if the wall thickness and diameter are identical. But chemical composition, heat treat will determine whether the spar permanently bends in 10 knots or 30 knots, whether the spar snaps in 20 knots or 50 knots. When people start measuring the vaiation of deflection, all they are really doing is measuring the wall thickness, this can also be done by measuring the weight.
     
  15. nedsbeds

    nedsbeds New Member

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    So taking that one step further, what you are saying is that the chemical composition and heat treatment of a spar has no effect on racing performance.... ;)
     
  16. wessel

    wessel Member

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    If the spar snaps in a 15 knot breeze -- then you don't finish the race. I guess that would be considered performance.

    It would seem to me that the original spars were *off the shelf* back in the 70s when they locked down the design for the Laser and the industry has moved on past to new alloys and processes today, so after following the long thread about the legacy sailcloth in the sail, I wonder if the builders are required to keep the same alloy and process alive for the legal spars and this would keep the cost of production up.
     
  17. jotag

    jotag Member

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    Aluminium heat treating consists in three phases: solutionizing, quenching and artificial ageing. Because it changes properties with time. Aluminium alloys do not allow to control hardness like the steel. If chemical composition is right, then laser spars are well made or not depending on heat treatment. The only way to control them is by hardness tester. Webster scale. Many times, even in world championships, sailors complain about stiffness and many times they bend. In our factory we always test one by one.
     
  18. Andy B

    Andy B Member

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    I may just have been unfortunate but I broke a top section and my local chandler only had a replica parts in stock so I bought one so I could sail the next weekend. It was a disaster, the boat would not point and I could not keep up with the sailors I usually race with. When I checked, the spar was very soft and it's weight was 10% to 15% less than a selection of class legal spars I weighed in the dinghy park. Bought a class legal spar and my old boat speed came back. I'm sure there are good replica spars out there but you do have to be cautious. I just buy from Laser now and keep a spare in the garage.
     
  19. jotag

    jotag Member

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    Why don´t you try ours???. Intensity Sails support this page.
     
  20. AlanD

    AlanD Former ISAF Laser Measurer

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    As explained above, stiffness, how much your mast flexes is a factor or Young's modulus, diameter and wall thickness. Young's modulus is fixed for all alpha phase aluminium alloys irrespective of the heat treatment or hardness and chemical composition (alpha phase alloys only). The yield point, ultimate tensile strength, where the mast permanently bends or breaks is something controlled by the heat treat and chemical composition and that can be indicated by the hardness, although it only an indicator, it can be wildly inaccurate, the only true test for YS and UTS is tensile testing.

    AlanD former Metallurgical Engineer.

    Btw the depending on the alloy natural aging does occur and not all aluminium alloys will age, this is very much controlled by the chemical composition.
     
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