Ideas for Improving the Top section

Discussion in 'Laser Talk' started by rippa, Nov 5, 2007.

  1. rippa

    rippa Member

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    Recently there a more and more reports of broken top sections of the Laser mast and many anticipate a move towards a carbon fibre top section. It would seem that we have not explored all options regarding the aluminium part. Discussion: increase the lenght of top section that slides into the bottom section and/or put a sleeve, similar to that in the boom, into the lower 50cm of the top section. We will see dramatically fewer broken top sections plus a more organic curve of the whole mast under load. Old top sections could be upgraded with a sleeve and would not become obsolete.
     
  2. Clive Humphris

    Clive Humphris ILCA Technical

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    Re: Top section

    I think the idea of a sleeve has a lot of merit. The other idea that should also be considered (and has also been mentioned in the past) is the idea of a rivet less collar. This rivet less collar would essentially be a 305mm deep cup that would insert in the bottom section and accept either end of the top section which would be sealed at both ends with the current top plug. This would overcome the stress concentration and corrosion problems associated with the current rivet collar part.
     
  3. computeroman2

    computeroman2 Member

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    Re: Top section

    I don't see how lengthening the upper section would help. If the fit is tight, like it should be, adding more length in the mast won't take load off of the point right where the lower mast ends, it would only make the whole joint stiffer (but still just as likely to break). You could make the uppers out of thicker aluminum, but then they wouldn't depower as much. Carbon lasts longer anyway- I think it is the way to go.
     
  4. rippa

    rippa Member

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    Re: Top section

    Mountain Bikers have gone through the discussion "carbon against aluminium" for some time and lately there are some amazing examples of very light and stiff alu bikes on the market-at half the price of a carbon product.
    Consider that:
    a) the Laser Class has adopted change in the past only in mini steps (e.g. sails) it is unlikely that I as a Grand Master sailor will ever enjoy sailing a Laser with a carbon mast.
    b) Aluminium is a common element on this earth although it gobbles up a large amount of energy in the production process.
    c)Carbon fibre composite requires oil based materials which will be in short supply for some time to come.

    I will fit out one of my permanently bent top sections with a sleeve this summer and will let you know what happened during training.
     
  5. Chainsaw

    Chainsaw Brmmm Brmmm

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    Re: Top section

    As far as I know, the furthest you would need to insert the top section into the bottom section from a strutural point of view is 6-8 times the diameter of the tube. I think it's about that now.

    Mixing carbon and alloys is not a good idea from a corrosion point of view. You'd need to make sure that the collar was made of a completely neutral material and free from any salt residue.

    It may be time to go the whole hog into a carbon fibre mast. All these half pie additions to the laser, attempting to modernise without modernising, are ridiculous. Just do it properly.
     
  6. SFBayLaser

    SFBayLaser Member

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    Re: Top section

    Just to push the discussion along a bit... here are a couple of pics of the composite section being considered for the Radial right now. These aren't very good photos, I must admit, but hopefully you can get a feel for what the spar looks like from them.
     

    Attached Files:

  7. SFBayLaser

    SFBayLaser Member

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    Re: Top section

    PS I believe there are a set of these spars getting a work out in Australia right now though I think they are on the East Coast.
     
  8. Wavedancer

    Wavedancer Upside down? Staff Member

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    Re: Top section

    Reminder: the carbon top section (if approved) will only go with the radial rigs.
     
  9. SFBayLaser

    SFBayLaser Member

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    Re: Top section

    And 4.7s.

    But... it is certainly worth debating whether or not these composite spars (they are only 5% carbon so don't deserve the label "carbon spar" in my book) might be the answer to the aluminum top mast problems.

    Just throwing that out there to see what people think.
     
  10. 49208

    49208 Tentmaker

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    Re: Top section

    Perhaps it helps to state the problems ?

    1. Inconsistent sections resulting in changes in stiffness - IIRC this is caused by both material spec and the dies producing a thicker section the more they are used..

    2. Breaking at the collar caused by the hole thru the spar for the rivet.

    3. Perm. bends caused by both mis-use and inconsistent material


    Anything else ?


    IMHO, The class should fix #2 right now, that doesn't need a change to a composite spar, I believe there was a proposal for a change that would eliminate having to drill the section. Any progress on that ?

    I don't see #1 and #3 getting solved if we stay with aluminum.
     
  11. SFBayLaser

    SFBayLaser Member

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    Re: Top section

    I have heard two proposals for this:
    1) glue the collar to the mast instead of using a rivet. The WC has been told that this has been investigated but that there is not a reliable adhesive that would work as effectively as the rivet.

    2) Develop a mast insert to replace the collar. If I understand correctly, there are several issues but the primary problem is the combination of tolerance (e.g. the variation in inner diameter of the bottom section) versus strength. There was a very serious investigation of this just a few years ago.
     
  12. vtgent49

    vtgent49 Member

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    Re: Top section

    Couple of thoughts:

    Problem 4 is the knuckle-type bend at the joint, that causes the sail to look so bad in some photos.

    A boom type sleeve could be used to both stiffen the stress point, and maybe help with 4. At little cost and hardly causing any obsolesence to old rigs. If someone wants to risk the bend/break to have the de-power effect, then that's their choice. The sleeve could be sliced or taper cut to spread the stress point out, instead of just moving the knuckle up.

    I also think that the rivet could be moved to the bottom half of the collar. I'd bet this would eliminate any break passing thru the rivet hole. Bending type failure might be the same, but we all know a bend is better than a break, as it saves the sail, makes getting home easier, and it allows the spar to be straightened/reversed. This one change is a no-brainer in my mind.

    Since the "Cf" spar is being aimed at lightweights/depowering, then what's gonna happen when a 180 lb master goes out in 25+?

    Al
     
  13. 49208

    49208 Tentmaker

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    Re: Top section

    Thanks for update - amazing that with all the adhesives the aerospace guys are cranking out that we can't bond aluminum and plastic.. back to the mixing pail
     
  14. rippa

    rippa Member

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    Re: Top section

    Funny how the sleeve works on the boom. Same diameter.
     
  15. computeroman2

    computeroman2 Member

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    Re: Top section

    The boom sleeve isn't a snug fit in the tube- there's about a 16th to an 8th of an inch of clearance. I just added a sleeve this summer, and was a little concerned about the space. The sleeve doesn't even start to help until you're vanged hard. I don't see a sleeve as helping that much, unless it was four or five feet long.
     
  16. Ross B

    Ross B Guest

    Re: Top section

    which would add a good bit of weight aloft, and possibly hurt righting movement
     
  17. bjmoose

    bjmoose Member

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    Re: Top section

    Hi Tracy,

    In the past you've mentioned that the class seems to be extremely resistant to any sail cut or material change that would represent a "game changing" difference.

    The sail costs $500+ and wears out relatively quickly (depending on who you ask)

    The upper mast section costs about $200, and breaks less frequently (depending on who you ask.)

    Personally, I'd vote for both changes. But if we can't sell the class on a more durable sail, the relatively decreased cost/benefit of an upper section seems like a tough sell to me.

    The only difference is the catastrophic, sudden unexpected failure of a top section can cause people to lose what otherwise would have been a fine showing in a regatta. So I can see folks to whom that has happened voting for a more durable section to keep it from happening again.
     
  18. madyottie

    madyottie Apprentice

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    Re: Top section

    I'd go for a composite section, even though I've not lost a major regatta due to a failure.
    Like a lot of people though, I've saved my pennies for a new sail, only to have the top section snap on one of the first few outings, rendering that nice pretty sail totally poked!This wouldn't bug me so much if it had been 30 knots, but considering that sail had barely been worn in, it was kinda annoying!

    Anything that might help preserve the racing life of a new sail would be good in my books. If it was marginally stiffer than the ali one, it might even prevent some of those ugly creases which get blamed on the joint! Or at least it might stop the arguments! ;)
     
  19. rippa

    rippa Member

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    Re: Top section

    I am sailing in country Western Australia and I am out there by myself regularly in 20 knots+ offshore and I do not feel comfy with that top section. The overall length of the common shark here is about 2 feet longer than my Laser.

    If someone fits a sleeve to their boom and it is not a snug fit, they chose the wrong sleeve, my factory sleeve in my boom sits snugly.

    I am currently on the road, when I get home I will put a sleeve in and will report back to anyone interested. Should I not be able to find a sleeve that fits perfectly I will say sorry to comuteroman2.

    Same with the glue. Do not abandon a good idea because of hearsay that it is not possible.
     
  20. dougreynolds10

    dougreynolds10 Member

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    Re: Top section

    If the rivet in your top section is looking worn or rusted if you replace it does it extend the life of the spar?
     

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