How To Avoid Ligthening Designing A Sailing Yatch

Discussion in 'Boat Design' started by metin_mehel, Apr 11, 2014.

  1. BertKu
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    BertKu Senior Member

    Indeed, because you have up to many burst of short current pulses (up to 40 -50) the pulse has a shape , which contains 1st, second, third , fourth etc ... hundred harmonic, for those very high harmonics, the inductive resistance is very high for those upper harmonics and then flashes start being formed at those bends. Like I have said before, the trick is to re-route the lightning surge via the shortest way and lowest resistance and that applies for the upper harmonics as well. Not to suppress nor block. Thus no coils or part there off by bending the copper wire. Aluminium has a higher resistance and is thus not really suitable for lightning conductors.

    For primary protection, I agree. Not for secondary protection a kind of Faraday cage protection can save your life. Bert
     
  2. powerabout
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    powerabout Senior Member

    although objects get fried on the outside of steel ships, rarely does anything go bang inside.
    I wonder if thats the faraday cage or the isolated earth components?
    One of my mates has isolated earth on all his kit in a yacht and 15 years or so no issue in Singapore. Every yacht in Singapore has replaced kit due to lightning ( some we call lightning magnets, are always replacing kit)
     
  3. BertKu
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    BertKu Senior Member

    Yes, the electrons are moving along the outside surface layer, not penetrating deeply into the surface layer. Indeed a steel ship is a kind of Faraday cage.
    Powerabout, could you explain more what you mean with an isolated earth on his kit. What do you mean with the kit?. Bert
     
  4. powerabout
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    powerabout Senior Member

    all IMO approved equipment on board has isolated earth as in the housing is not at the same voltage as the low side of the 12/24v
    The 24v on a commercial vessel is floating and not on the ship ground.
    What my buddy did was to add 12v power supply on board that has its minus isolated and then ran that to each accessory and ensured their case did not earth on board.
    Then he also added optical isolators to all data feeds ( as per a commercial vessel).
    It seems to have worked so far?
    Kit is British slang for equipment/gear
     
  5. BertKu
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    BertKu Senior Member

    Metin, just because one large airplane has disappeared , that does not mean you should not fly anymore. You can still go safely out onto the sea, as long you understand what to do, when you lend up in the middle of a storm with lightning. You probably have a greater chance to get thrown overboard then to pick up a direct hit. In your part of the world, the lightning strikes are not as severe as in some other parts of the world. However, on your boat. I would not stand up, but lie down and make yourself the lowest point and move a little more away from the mast. ( and pray very hard) There are many people who have survived close to a direct hit, but the healing of the wounds will be very difficult when a side flash start rolling and hits you. You should just look at your boat and make logic decisions in how to protect your boat the best way.

    Not sailing and having your boat anchored in the harbor, I would still advise to consider a copper lightning protection from the top of the mast, without bends to the sea. Your investment is probably a lifetime savings and a few dollar more to create a basic good solid lightning conductor is worthwhile, even anchored in the harbour. Bert
     
  6. BertKu
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    BertKu Senior Member

    Hi powerabout, thanks for the explanation. Normally commercial boats are steel boats, but on a GRP or wooden boat you take a risk.
    Bert
     
  7. SamSam
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    SamSam Senior Member

    I have an old lightning protection system that I took off a barn, the wire conductor is about 1/2" in diameter, a coarse braid of small copper wires but the cable is hollow.

    It looks like this, but as I say, the cable is hollow. I asked why and was told that with large doses of electricity like lightning strikes, the current mainly travels on the surface so a hollow cable is just as efficient as a solid cable of the same size. I believe that was the theory back around 1900, I'm not sure if it still is or if it was ever valid to begin with, but patents were issued for different hollow cable configurations.



    [​IMG]
     
  8. BertKu
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    BertKu Senior Member

    Surviving a direct hit

    Hi all, Sometimes readers think I am a flipping cucumber, but I read a few days ago in the monthly magazine "Sailing South Africa", that this person survived , together with friends, who never had been sailing before, a direct hit on their sailing yacht on the lake by Johannesburg. I know that that area is known as a very high severe lightning area. It proofs, that it is possible to survive a direct hit, provided the resistance from the entry point of the lightning strike to the water is so low (copper direct line preferable) that the heat and surrounding magnetic field is low.
    refer http://www.sailing.co.za , "Lightning a real life experience".
    Bert
     
  9. BertKu
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    BertKu Senior Member

    Does anybody know. If I copy that article from the Sailing magazine and mention at the bottom : copyright and published by "Sailing South Africa", am I in copyright infringement? or not?.
    Bert
     
  10. powerabout
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    powerabout Senior Member

    direct hit is no big deal for the occupants that I have every heard of and know plenty who have been on board in direct hits
     
  11. Eric Sponberg
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    Eric Sponberg Senior Member

    Probably not. Magazines actually like to have their information passed around as long as it is properly credited, as you suggest. You might add the link to the actual on-line magazine so that others can go to it at their will.

    Eric
     
  12. BertKu
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    BertKu Senior Member

    Thanks Eric ,
    The problem is that this link only allows a short "headline", but the full article is not accessible by non subscribers to this magazine. I will play it safe and tomorrow I will contact the editor.
    Bert
     
  13. portacruise
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    portacruise Senior Member

    Can't really do AVOIDANCE within a hundred feet, though most of the above suggestions will be helpful AFTER a strike occurs.

    "Cloud-to-ground lightning strokes initiate high in thunderstorms, miles above the surface where ground objects have no effect. Even after initiation of the discharge, the downward-moving stepped leader is 'blind' to objects on the ground until it is very close to the ground, within 50 to 100 feet. At that distance, lightning will strike within the very small area it is already descending in, regardless of any devices nearby that claim to divert or prevent the strike. For example, a photograph exists of a lightning strike to the Merchandise Mart building in downtown Chicago. Merchandise Mart is very close to the 1,700 foot tall Sears Tower, yet not even the Sears Tower influenced the ground connection of this close cloud-to-ground stroke."

    Makes sense to me and seems like a credible source, but who knows: http://stormhighway.com/protection.php

    Maybe the only avoidance would be to have a position where there is at least one taller and more conductive profile within 100 feet, YET not too close where you can have sideways jump (10'?) to your position.

    PC
     
  14. BertKu
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    BertKu Senior Member

    Hi powerabout,
    There seem to be a split opinion on this issue.
    The one states, noway will a sailor on a yacht at sea be able to withstand a direct hit.
    Others like me and you say, Provided you have proper thick multi stranded copper from top of mast (not an aluminum mast alone, what so many sailors/builders have) down to a proper checked , free from algae and good water contact base plate , you will survive.

    Thanks, I agree with you.
    Bert
     

  15. BertKu
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    BertKu Senior Member

    Hi Porta,
    Very interesting article and examples. The problem is that most of it is written for strikes on land. At water, there are other conditions and considerations. The most important one, I feel is used wrongly, is the aluminum mast as lightning conductor. One can easy calculate the difference in Voltage potential at let say 50.000 ampere. Like somebody said, Aluminum has often a protective layer and reduce the conductivity. Also the resistance is higher than copper.
    At 50.000 Ampere, it would mean 52,5% more for the same square surface area. That could be the extra voltage to create side flashes or induce more than 20 milli Ampere through your heart, when you become the secondary part of an "air transformer". Nobody can dispute that our body has lots of conductive liquid. The magnetic field created by lightning loves it to test you out. Play it safe and use thick or multi stranded copper wire.

    I don't know whether I should suggest to have the copper wire in the center of the aluminum mast. I have no means to have such proposal tested. Bert
     
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