dyneema and lightning...

Discussion in 'Boatbuilding' started by robwilk37, Jan 28, 2012.

  1. michael pierzga
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    michael pierzga Senior Member

    Ya...the lightning , energy , had no way to escape the boat. Ive also known best practice grounded boats ,hit in the water ,to be destroyed. I saw a swan with its alloy toe rail blown off the sheer clamp.

    Best practice is not a guarantee. Personally , when at sea, I steer clear of lightning even if means hours lost in transit.
     
  2. michael pierzga
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    michael pierzga Senior Member

    For big yachts out of the water its best practice to ground the yacht.
    Shipyards mostly do this to prevent electrocution of workmen.

    On a metal yacht this typically means dropping an Anode, then bolting a heavy copper conductor to the anode stud and the shipyard ground plane.

    I dont know if this is effective against lightning strikes.
     
  3. Stumble
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    Stumble Senior Member

    I guess my point is that the effects of a major hit are so poorly understood and the damage potential so severe, the best you can do is just follow best practice for grounding, and not worry about it any more. I guess theoretically dyneema would help to channel lightning into the mast for disposal out the grounding plate, but in all honesty I don't think it would make much difference.

    As far as dyneema as standing rigging, it works, has for years, has the same recommended service life as wire or rod, and weighs 1/7 what wire does for less money. When I replaced the rod on my race boat I didn't go with dyneema because it was no new, but I am now wishing I had.
     
  4. michael pierzga
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    michael pierzga Senior Member

    I sailed with first gen fabric rigging 18 years ago on diagonals. Good stuff but UV and Chafe were problems. I would imagine that it is the same now only the rigging is cheaper
     
  5. Stumble
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    Stumble Senior Member

    Uv on dyneema is certainly an issue, but the degredation is again predictable. It goes realatively fast at first, but then slows down, and eventually flatlines over time as the outer fibers act to prevent the core from taking damage. Since the line is speced at multiples of the necessary breaking strength one of the ways to determin when UV has become a problem is when creep starts to accellerate. With uncoated rope this process takes about 8 years (the same as the replacement interval on wire or rod).

    Chaff is certainly an issue, and you have to work to minimize it, but absent someone taking a knife to your rigging, isnt really a problem. Just round over edges, and remove burrs. In fact dyneema is actually the prefered choice to make chaff resistant coverings for other things. Like ANSI level 5 cut resistant gloves.

    I would also point out that dyneema is pretty much impervious to chemical attacks, though it does have some sensitivity to very high PH bases (13.7 or higher... this is higher than caustic lye). But it is impervious to gas, diesel, water, solvents, acetone, ect...

    And I just noticed that if you burn it, all it releases are Water, and Carbon Dioxide, so no harmeful vapors.
     
  6. MechaNik
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    MechaNik Senior Member

    Stumble, Kevlar is a very good choice for a yacht rig. Bare in mind it is a brand name and there are many versions available. There are probably more yachts with it combined to rod rigging than every other fabric used. It does not make good running rigging due to the bending required. Lifespan has certainly been proven.

    There should also be a distinction between racing and performance cruiser when talking about fabric rigging choice. Also weather you can tolerate failures and constant rig tuning.

    How big, try southern spars 64m carbon rig on Vertigo. I'm sure that wasn't a whim when choosing the EC6 system for such a yacht.

    There are many discussion and research papers about sizing conductors for sail boats and dealing with isolated grounding. It seems the biggest issue is that lightning strikes sometimes aren't the biggest issue when building a boat.

    Personally I think that removing rod rigging would make it more likely a conductor would attract the full lightning strike, perhaps isolating any damage better.
     
  7. Stumble
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    Stumble Senior Member

    Yup, you are right, I was mistaken about the Kevlar rigging using a trade name. So there is another option.

    Do you know if it is a monofilament like PBO, or is it more like rope?
     
  8. MechaNik
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    MechaNik Senior Member

    The Aramid/Kevlar is normally a fine strand cable that needs a mechanical compression fastener such as a cone and spike because knots and braids don't work.
    There is normally a plastic protection sleeve over the line which gives it it's noticeable appearance.
    I would have a guess that if you wanted to use fabric rigging on a boat other than a race boat ie you want insurance, then you would need to have system in place to monitor wear and strain (creep).
    For example with rod rigging you would have the new pieces dimensions and length. Then you would need to present how much elongation and thinning of the cable is acceptable over time.
     

  9. Stumble
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    Stumble Senior Member

    As far as insurance is concerned... This is an area of law I practice in a good deal. The following is not to be considered legal advice, but a statement of experience.

    Most insurance companies don't know, or care what your rigging material is made out of, and there is no reason to believe that a claim would be denied because you are using Dyneema, PBO, or even dental floss. There might be an issue if the surveyor won't pass the boat for survey purposes, but that's it.

    The real question though is if the specific rigging on the boat is what is called 'seaworthy'. In this seaworth is a term of art in maritime law and doesn't really mean what you might think. But generally it can be construed as meaning that the boat and it's systems are in reasonable condition at the time the voyage began for the expected conditions, and expected duration. The problem here is that since most rigging manufacturers state a lifespan of 7-8 years for rigging (including dyneema), if your rigging is older than this, unless you have had x-ray inspection or dye testing done there is a possibility that you rigging is not seaworthy regardless of the material it is made out of.
     
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