Lightning

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  • 17 Jan 2022 05:43
    Reply # 12269732 on 12250597

    I have an aluminum boat with an aluminium mast and while I worry about a lot of things, lightning isn't one of them.

  • 16 Jan 2022 19:04
    Reply # 12268391 on 12250597

    How to connect the mast to the lightning ground plate is the question. As I understand it, a lightning induced pulse of electricity (average 1,000,000,000 joules or watts/sec) isn't all that keen to go around bends in conductors. However, I'm inclined to think that it's rather tricky to connect the bottom of a mast to a grounding plate without putting bends in the conductor.

    Some insurance reports suggest that, having travelled down the mast, lightning has a tendency to make for the waterline of the boat, peppering the hull with small holes as it leaves (fibreglass hulls).

    In an earlier thread, there was a video of a wooden telegraph pole being struck by lightning and being blown to smithereens.

    Like many of you, I dare say, I've read quite a bit on lightning and protecting a boat from it. There is a mass of contradictory information out there and a few companies marketing products of questionable effectiveness, based on claims made from questionable science.

    My feeling is that lightning will basically do whatever it wants, irrespective of what measures have been taken, but I could be wrong...

  • 15 Jan 2022 22:55
    Reply # 12265865 on 12250597

    A golden coin? Now you are getting into very mythological territory! However, copper coins are still used by many wooden boat owners, and while it seems like a superstition to place a coin in the mast step the copper actually prevents rot in the base of the mast, which is vulnerable to gathering rain water.

    I always place one in the mast step of our 140 year old open boat and at the end of each season the alloy is usually very corroded to the non-copper metal in the coin. It's the smallest expense! 

    Somebody on the forums posted pictures of something similar last year.

  • 15 Jan 2022 21:45
    Reply # 12265758 on 12262354
    Anonymous member (Administrator)
    Anonymous wrote:The current on the surface (skin effect) is an AC phenomenon.  DC does not behave that way at all.  Lightening of course is DC.

    Keel bolts are not available on all boats.

    How many junk rigs have sustained lightening strikes?     As a percentage of sailboats in total they are a very small percentage.   BoatUS states that the percentage of sailboats struck by lightening is about 3 per 1000.   I assume that is annual.   Power boats 5 per 10,000.   The difference is obviously the mast height.  Junk rigged boats usually have a lower aspect ratio and shorter mast, so I would expect the percentages to be somewhere between.   An unstayed wooden mast would seem to be a less likely "target" than an unstayed or stayed aluminum mast.

    A free standing fiberglass / epoxy mast would be an insulator.... but such a thing does not to my knowledge exist.

           I've heard that painting lambs blood on the "door post" of the companionway solves the problem.....but only if you are Jewish ;-)   Something I learned in sunday school as a child....

    Bonjour

    The "lambs blood " method, as efficient it may be, may induce some issues with the Vegans.; probably more than any lightning stike on the boat !

    I would suggest an alternative that has proved to be efficient from several centuries that consist in burying  a golden coin under the mast while stepping it. Otherwise the seamen would have stop that practice !

    I've written stupid things. The lightning is both high tension AND high current. It is neither AC or DC but an intense inpuls.

    For a more scientific aproach to lightning there is a nice PFD presentation on the subject (aircraft oriented I'm afraid !) :

    search on the web for : sikorsky lightning protection  rob majkner

    https://skybrary.aero/sites/default/files/bookshelf/3553.pdf

    Eric








    1 file
  • 14 Jan 2022 17:43
    Reply # 12262354 on 12261618
    Anonymous wrote:

    Bonjour

    As the electric curant remains at the surface of the conductor it would be easier and more efficient to use a flat conductor. It could be plain or a more flexible braid (you should not have any loop).

    A way to ground the lightning on « pointies »  is to use the mooring chain in loops dropping in the sea from around the shrouds. It could be around an aluminium mast.

    French and perhaps European regulation requires to link the bottom of the mast to a keel nut with a flat copper braid.

    In lightning the voltage is very important but the intensity is rather small. So the surface of the grounding is not that important. On an aircraft the groundings are the little sort of brush that you may see at the wing trailing edge. But if the lightning doesn’t find a proper way it will dig a hole to the sea (through the hull for example).

    Eric


     The current on the surface (skin effect) is an AC phenomenon.  DC does not behave that way at all.  Lightening of course is DC.

    Keel bolts are not available on all boats.

    How many junk rigs have sustained lightening strikes?     As a percentage of sailboats in total they are a very small percentage.   BoatUS states that the percentage of sailboats struck by lightening is about 3 per 1000.   I assume that is annual.   Power boats 5 per 10,000.   The difference is obviously the mast height.  Junk rigged boats usually have a lower aspect ratio and shorter mast, so I would expect the percentages to be somewhere between.   An unstayed wooden mast would seem to be a less likely "target" than an unstayed or stayed aluminum mast.

    A free standing fiberglass / epoxy mast would be an insulator.... but such a thing does not to my knowledge exist.

           I've heard that painting lambs blood on the "door post" of the companionway solves the problem.....but only if you are Jewish ;-)   Something I learned in sunday school as a child....

    Last modified: 14 Jan 2022 17:46 | Anonymous member
  • 14 Jan 2022 10:59
    Reply # 12261618 on 12250597
    Anonymous member (Administrator)

    Bonjour

    As the electric curant remains at the surface of the conductor it would be easier and more efficient to use a flat conductor. It could be plain or a more flexible braid (you should not have any loop).

    A way to ground the lightning on « pointies »  is to use the mooring chain in loops dropping in the sea from around the shrouds. It could be around an aluminium mast.

    French and perhaps European regulation requires to link the bottom of the mast to a keel nut with a flat copper braid.

    In lightning the voltage is very important but the intensity is rather small. So the surface of the grounding is not that important. On an aircraft the groundings are the little sort of brush that you may see at the wing trailing edge. But if the lightning doesn’t find a proper way it will dig a hole to the sea (through the hull for example).

    Eric

    2 files
  • 14 Jan 2022 08:51
    Reply # 12261516 on 12259758
    Anonymous wrote:
    Kris wrote:

    I plan to use a copper plate, about 1 square foot. Copper surface is an antifouling by itself. Copper plate dump in the water requires copper wire to be connecter to, not aluminum one, I think. Kind of expesive set.

    Hi Kris,

    If I remember correctly your boat has two tabernacles for the masts. How do you plan to connect the aluminum mast, in a wood tabernacle, to the copper plate? 

    Both tabernacles are located in the proximity of wells: Main next to the outboard engine well, foremast next to the chain locker with the drain hole in the bottom. The 6mm (1/4") rod, aluminum or copper, will go from the mast hinge proximity to the opening in the well/bottom out to the grounding plate. I am not sure whether to use copper or aluminum set. With alu I avoid electrocorrosion, but am not certain how the alu plate will behave in the water. With the copper I am down with some funds and have sensible connection between mast and thr rod. However this connection is up, open and easy for inspection and protection with a greese or so. The graunding plate want to fix to the bottom from outside with small screws and epoxy.
    2 files
  • 13 Jan 2022 17:08
    Reply # 12260054 on 12250597

    I've heard of bermudan rig boats putting jump leads from their shrouds into the sea to divert the electricity from passing through the boat.


    Don't know how that might be effected with a free standing rig.

    Maybe from below the lower batten to over the side?

    Maybe 3-4 lines from the lower mast to create a faraday cage effect?

  • 13 Jan 2022 14:53
    Reply # 12259758 on 12259080
    Kris wrote:

    I plan to use a copper plate, about 1 square foot. Copper surface is an antifouling by itself. Copper plate dump in the water requires copper wire to be connecter to, not aluminum one, I think. Kind of expesive set.

    Hi Kris,

    If I remember correctly your boat has two tabernacles for the masts. How do you plan to connect the aluminum mast, in a wood tabernacle, to the copper plate? Right now I have an aluminum mast completely disconnected from all the other metal in the boat. this is on the list of things to 'fix' before I find myself out in a thunderstorm.

    I am also not sure exactly how to attach the plate to the boat. Epoxy and glass seem like the obvious choice, but I expect the metal could get hot conducting a lightning bolt (!) to the earth. Could this melt the epoxy and open up a hole in the bottom of my boat?

    Last modified: 13 Jan 2022 19:15 | Anonymous member
  • 13 Jan 2022 07:06
    Reply # 12259080 on 12250597

    I plan to use a copper plate, about 1 square foot. Copper surface is an antifouling by itself. Copper plate dump in the water requires copper wire to be connecter to, not aluminum one, I think. Kind of expesive set.

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