MikeJohns

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About MikeJohns

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    Hobart

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  1. MikeJohns

    Warps reels

    Netting rope stuffing bags are good for long mooring lines. they can be washed/hosed in the bag , left on deck or in a deck box or slung below when dry. When single handed it's best to run the line out of a bag in the dinghy, then you can fix any run-out snarl-up immediately.
  2. MikeJohns

    Lightning Strike Mitigation

    No, not the total by any means. Keep worrying ! It’s only an indication of the ratio of what they term 'significant cost' claims, and only on claims to one companies office in Singapore. Did you have any protection fitted ? Zonker's method above would certainly help.
  3. MikeJohns

    Lightning Strike Mitigation

    Claims make poor statistics except for insurers. From shielded water area theory you’d certainly expect a ratio around 2:1. Globally there are areas where there are virtually no multihulls and other areas where they predominate. Same with Lightning, in some areas it’s almost unknown in others it's almost a daily event. Referring to the claims for SE Asia for one insurance company from the Singapore office, over half the claims for lightning strike were for sailing catamarans but they represented one fifth of the insured fleet of sailing craft. It’s possible, thinking about it, that that’s explained by geographic anchorages. Overall numbers are still relatively low, from memory over a 3 year period around 12 sailboats with significant claims. Probability for a claim was still low, around a fifth of a percent. Also the insured craft that may have been struck but had no damage aren't counted. Anyway the claims are minuscule in comparison to claims for collision and grounding so it’s never going to be considered a risk requiring mitigation by insurance
  4. MikeJohns

    Batteries

    Ditto for Trojan. I've had Sonnenschein Gell that were also very good.
  5. MikeJohns

    Lightning Strike Mitigation

    Multi ( and multi multi ;-) hulls are notorious for attracting lightning. Cats are an order of magnitude higher apparently. A friend was quite happy when he had ALL his outdated electronics replaced under insurance when his boat was struck. A quick upgrade that added a lot of value to his boat when he sold it later. Your friend is right. Small non conductive hulled boats below around 35 feet are extremely hard or next to impossible to fully protect. So are non conductive hulled boats in fresh water. Although the larger the boat gets the better the protection gets. But although smaller boats might lose their electronics, you can still stop the boat sinking by using relatively simple installations of down conductor and ground plate. More recent concerns both by regulatory bodies and insurance companies is new battery technologies and lightning both initial and secondary effects which haven't even been considered by the battery manufacturers.
  6. MikeJohns

    Lightning Strike Mitigation

    The level of protection depends on the cost benefit trade-off. It’s expensive to fully protect any terrestrial installation (especially in your situation), and generally requires some expert level design, but 100% protection it is achieved routinely. On boats and ships it's no where near as complex. Sailboats offer a near perfect position for an air terminal and the entire craft lies within the zone of protection.
  7. MikeJohns

    Lightning Strike Mitigation

    The crux is that it's made attractive ! The ground leader forms from a good discharge point and the downward path meets one of the upward. That's why a grounded spike or sometimes metal sphere is used at the top, it initiates a leader from the ground upward and that a strike will go direct to the spike, not to any other part of the boat. So yes the downward path is pretty random, but within a 45 degree cone that leader will go to a lightening rod. The attached pic shows a ground leader going up from a boat mast, the non contact downward leaders and the final contact that creates the plasma channel.
  8. MikeJohns

    Lightning Strike Mitigation

    It's not air anymore, it's a plasma and is a very good conductor indeed. If you did as you said it will all go via the mast. The rest will rise in potential for a few microseconds each pulse given the mast resistance but it won't develop enough voltage to break down any other conduction path. Oddly enough WRT conductor sizes, sometimes a small cable can simply act as a leader and once it vaporizes the plasma channel takes over. No good for subsequent strikes but.
  9. MikeJohns

    Lightning Strike Mitigation

    A quick calculation shows that even the ideal of a film of pure seawater 1mm deep over a surface has a resistance of a magnitude of hundreds of ohms per meter of path. That's not low impedance. In consequence it will vaporize instantly. I think you are confusing skin effect with charge distribution. Skin effect is not "on the surface" as you say but within the conductor growing in conduction depth in an order of magnitude of one mm per microsecond. A lightening current pulses main discharge conduction transient (say 100 thousand amps) lasts around 30 to 40 microseconds. That's all in one direction and is entirely a Direct Current transient (It's a capacitive discharge). Then the magnetic field collapses around the plasma channel and a lower reverse current flows for a similar time, this then in turn reverses oscillating like a classic LC circuit but rapidly damped. Then the charge redistributes in the cloud and the entire event happens again sometimes 2 or 3 times. So there's lots of HF but the main discharges are transient DC.
  10. MikeJohns

    Lightning Strike Mitigation

    Sea water is a relatively poor conductor and rain water is an effective insulator. Conductivity ( S/m) of seawater is around five, Conductivity of boat building steel is around 6.3 million, there's no way a thin film of seawater could provide any similar protection !
  11. MikeJohns

    Lightning Strike Mitigation

    I think most of the world applies ISO these days for EM emissions. Military contracts come with some detailed specific standards all country specific but all similar, some better than others. The UK is quite detailed even down to wiring layout. The US provides separate installers guides for compliance. EMP is a big issue for them. A few years ago the US military introduced specific lightening protection (mainly electrostatics if the rest is allready EMP resistant). But lightening diverters from antennae and other sensors has become mandatory too. All vehicle manufacturers are now aware of the bonding earthing shielding and filtering requirements for EMC standards. When a design or layout prevents EM getting out of an enclosure or wiring loom for example it also stops it getting in.
  12. MikeJohns

    Lightning Strike Mitigation

    In high lightening areas, vehicle electronics failure from lightening strike is not considered a problem; it’s extraordinary nowadays if it causes any damage. Same for aircraft. Metal aircraft are innately protected. Composite aircraft embed an external conductive mesh for lightening protection. On aircraft, even a strike that fuses alloy aircraft skins doesn’t damage the electronics providing a few simple design rules are followed. There are various design standards from several sources, automotive electronics adhere to a similar standards. As for windscreen openings in metal bodies : Polarization of the low frequency EM wave is critical for it to enter, it doesn't get into holes very well, and if it strikes the roof of the aircraft or car, the EM field won’t enter even through the larger front windows, at least not at significant levels. The significant EM emission radiates outwards. Secondary EM from conduction of the charge are not significant providing cables are run together and microprocessors are screened . The same Spurious EM Emissions standards have actually made most electronics almost completely immune from nearby direct and indirect lightening related EMP.
  13. MikeJohns

    Lightning Strike Mitigation

    The commercial fleets of smaller coastal craft are a good indication. There was a lot of effort to make wooden boats safer when a strike would often jump or track from deck gear or mast base to the engine block vaporizing wiring on the way. The results were not pretty. The recommendation for proper protection is a straight low resistance conductor. For example the US Navy on non metal boats requires a copper AWG 0000 cable, installed in a straight line from a high point or metal mast base to a substantial immersed grounding plate . But metal boats don’t need anything other than a spike atop the mast providing the mast is metal and in contact with a metal deck. There are also protective MOV's across the power cables ( metal oxide varistors ) these are very cheap, effective and seldom installed for protection in leisure craft . The majority of metal vessels, boh ships and smaller craft are often unaware that they havee even been struck by lightening, and it very rarely if ever causes any issues providing antennae are kept within a cone of protection ( provided by a higher grounded conductor). Protecting sailing craft is no different, a straight low resistance path to ground is the recommended practice, relying on rigging shackle contact is not sufficient. There should be a good high current low resistance contact to a stay and it should lead on to a grounding plate. Rigging shackles have a low contact area and can have high resistance to lightening and aren’t considered an ideal conduction path. A sizable high current connection should be provided across rigging terminations if you rely on an immersed chain-plate. The area of the chain-plate may also be inadequate.
  14. MikeJohns

    Lightning Strike Mitigation

    I have direct experience here: We were hit in steel boat at anchor, It was an intense electrical storm with several strikes hitting the water close by. Only afterwards we were told by others that one discharge struck us directly. There was some visible discoloration of one of the stay terminations atop the mast. The only electrical fitting up there was the tricolor and it was OK. We had no damage to any electronics. The backstay was the HF antennae but both the ATU and the SSB radio were fine. I think metal boats and ships are generally pretty much immune.
  15. MikeJohns

    Girl with patreon account goes sailing in hot place

    A friend, a schoolteacher, had significant trouble with a 12 year old girls parents after a written report saying he thought she was precocious. The first he found out was the heavy hand of authority suspending him until review of a complaint that he'd made lewd comments about their daughter. Fortunately Paul was intelligent and confident enough to immediately go over their heads with the full facts including that he was ignoring the suspension.