dyneema and lightning...

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

  1. robwilk37
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    robwilk37 Senior Member

    im thinking of an all dux standing rig to composite chainplates but curious how it tolerates lightning ? conductive or not ? any special considerations ?

    thanks in advance...
     
  2. Stumble
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    Stumble Senior Member

    Rob,

    It has been done a good bit, but I am not aware of any boat with dux rigging that has been hit by lightning. It is actually a pretty good insulator, which I would imagine would help direct an electric strike through the mast, and out the keel. Though in a continuation of my experience with lightning strikes.... If you get hit, you get a new boat the damage is almost always to significant to repair.

    The reality is that dyneema is actually a pretty good insulator, but in the event it is hit by lightning, pretty much everything either vaporizes or melts.
     
  3. michael pierzga
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    michael pierzga Senior Member

    Very many large sailing yachts with fabric rigging. Perhaps ask an inurance company ?
     
  4. Stumble
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    Stumble Senior Member

    All the insurance companies care about is if it passes survey.

    The reality is That on the one boat i have seen that took a direct strike, which had a very secure ground path... The batteries exploded, all the electronics were cooked, through hulls were blown out, the hull was embrittled in places, even non-connected stuff was cooked... There is no way to protect from a lightning strike, it is just too powerful.
     
  5. michael pierzga
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    michael pierzga Senior Member

    Sure there is. Ive been struck by lightning several times with minor damage ...blown off antennae and once an exploding Navtec backstay insulator.
     
  6. Stumble
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    Stumble Senior Member

    Sure if you get hit by a little strike, or are just nearby. But a direct strike... Not a chance?

    A lightning strike can have 5 billion joules of electricity, and can reach tempratures of 54,000 degrees. Which is hot enough to vaporize metals and melt glass.
     
  7. michael pierzga
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    michael pierzga Senior Member

    It only get hot if you have a poor ground
     
  8. Stumble
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    Stumble Senior Member

  9. MechaNik
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    MechaNik Senior Member

    I have been struck on the mast twice severely. Once was a direct strike on the mast of a swan 65 that I personal saw happen. The lack of damage made it hard to convince anyone else we were struck, good installation and double pole breakers on the DC.

    Look for the mythbusters episode where they lightning strike a shower with properly grounded copper pipes.

    Either way Dyneema has not proved itself suitable for standing rigging in my book. Stick too PBO, Carbon, Vectran/Kevlar like all the big boys.
     
  10. Herman
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    Herman Senior Member

    In the old days, dyneema had a lot of creep. You kepy turning turnbuckles. Did they solve that yet?
     
  11. michael pierzga
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    michael pierzga Senior Member

    Direct lightning hit on moored boat using conventional best practice grounding... minimum damage

    Vectran is Creepy. As your suppliers for details.
     

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  12. Silver Raven
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    Silver Raven Senior Member

    G'day 'Nik' - Why would you suggest 'carbon rigging'? ? What grounding would you say the manufactoring people - making carbon rigging - would suggest for lightening proofing?? We're all out here waiting!!! james
     
  13. michael pierzga
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    michael pierzga Senior Member

    On The last carbon mast ,fabric rigged, boat I saw with lightning damage ,the energy traveled down the alloy mainsail track then grounded out to the deck structure.

    Again..ask an insurance company or a mast builder ,for their take on best practice for fabric rigging.

    Lightning strikes are fairly common...best practice must be re considered for new materials .
     
  14. Stumble
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    Stumble Senior Member

    Dyneema as standing rigging is a pretty proven application at this point. While it may not be for everyone, the design characteristics are pretty well known and understood, and if done properly isn't any more complicated than doing wire.

    Herman,
    Just a few basics, there are three types of stretch that can be seen in materials, and it is important to know which you are dealing with.

    1) constructional stretch - this is caused by the way the line or wire is manufactured, but once put under a load doesn't increase over time. Additional tension can increase it, but for dyneema the elongation at loads experienced as shrouds is very, very minimal once the line is tensioned once. Additionally a new splice has to be pre-tensioned to work out the constructional stretch, though a good rigger can predict what this elongation will be and make allowances for it.

    2) elongation - this is the elastic like properties of a material where when stretched it returns to its original length. Dyneema has about the same, or slightly less elongation stretch as steel cable of the same size.

    3) Creep - is the eventual elongation of a material when subject to extended periods of load. The specific type of dyneema used in rigging, called Dynex Duc, does suffer from higher creep than wire. However, the amount of creep goes up predictable based upon the ratio of static load to breaking strength. In rigging applications this is the primary design criteria, with the intent to keep creep at, or below .1" a year.

    Early attempts to use dyneema line generally didn't use the Dynex Duc, and typically used line selected for breaking strength not creep load which led to some problems. But once the systems became better understood there haven't been any real issues.

    MechaNik,
    I don't know of any boat anywhere that uses Kevlar rigging, it has way to much elongation for use in standing rigging, and honestly to much for running rigging. The stuff is like an elastic band. PBO is great if you can replace it regularly, and I have already seen two boats shatter carbon rod rigging from minor collisions. As for the big boys.... Well the open 60's are starting to switch to Dynex rigging, and given they carry 50,000psi of rig tension, I am not sure how much bigger you want to get.
     

  15. Stumble
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    Stumble Senior Member

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