Delta Loop HF Antenna for the Ariel

[ebb]

Once did extensive (for me) downloads on everything lightning I could find.
And I remember Prof Thomson's paper is in a thick file in a box here in the kitchen.
Altho I will have to read it again to remember anything!

My impression is that there is no route you can direct a strike to. If it wants
to come down the mast and jump sideways, it will. If lightning chooses any
or all at once of the stays & shrouds it will....... My conclusion,
remember, I really know nada about electricity, domestic or heavenly, is to
attach heavy duty battery cables to the wire at the forestay, backstay, and
top shrouds and throw the ends with wired-on chunks of zinc into the water.
Whatzat, baiting the lightning god?

I will go below if I can. If I can't, I'll pray that the Faraday tent works the way
you guys say it's supposed to. I will not ground the mast thru the interior
of the cabin. Last I heard, we ground to scintered bronze plate because it has
a lot of surface area in its structure. But somebody else says, wrong, it has to be
of lot of square footage of solid bronze to guanantee enough mass for a ground.
I have an objection to fastening a great hunk of metal on the boat underwater,
because I've also heard that a lightning strike can blow out a big hole....
right where the ground plate was.

If I remember, I'll wrap any loose electronics in an aluminuzed survival blanket.
And throw the breakers on the built in stuff. Make a cup of tea.

Really have misgivings about grounding the boat thru the interior.

[pbryant]

> My impression is that there is no route you can direct a strike to.

Benjamin Franklin answered that question a while back when he invented the lightning rod. Lightning CAN be directed, and it's a good thing too, or there'd be a lot of dead broadcast engineers and power utility workers. Seawater makes a pretty good ground. Fresh water is much more of a problem. If I were stuck in a thunderstorm in fresh water, and had enough all-chain rode to get a decent scope, I'd connect my common-point ground to the anchor chain and drop anchor to wait it out. A jumper cable from the forestay to the rode would do the trick.

The next time you are out in the country and see those high power transmission lines, look closely at the thin wire that has no insulators running along the top of the towers. That's a "lightning leader" intended to direct lightning strikes away from the three-phase power lines hanging from big insulators below.

Of course, the "more is better" approach of connecting everything, shrouds and stays, to the water like you describe has merit. But if you want continual protection, you may feel a bit silly dragging all those wires through the water all the time, and leaving them hanging at the slip. And there's also a problem with copper corrosion. Copper will rapidly dissolve in moving seawater because of an effect called: "erosion corrosion" (also known as impingement attack). If you stream copper wires underway, they won't last very long. Soon, you'll pull up stubs cut off at the waterline. But still, if you have no other protection, streaming jumper cables is a good form of episodic protection.

Bronze is chosen for "Dynaplates" because it doesn't rapidly corrode and doesn't develop an insulating layer on its surface. Cupronickel, a mixture of nickel and copper (10% nickel to 90% copper) which is highly resistant to corrosion from moving seawater, would also be good. Aluminum oxide is a bad conductor - so is copper when it forms compounds with sea salts (the "green stuff") which you will find rapidly develops on the submerged ends of your jumper cables. Pure zinc doesn't develop an insulating layer, and although it does corrode by dissolving, the corrosion is "beneficial" to any more-noble metals nearby. We're all familiar with that affect. If I used a bronze plate, besides being more expensive, it would corrode my aluminium outboard's prop. I already tried that. It's amazing how fast aluminum dissolves when its close to bronze.

>I have an objection to fastening a great hunk of metal on the boat underwater, because I've also heard that a lightning strike can blow out a big hole....right where the ground plate was.

Yes it can! It's like setting off a depth-charge right next to your hull! During a strike, a few thousand watts are dissipated into a small volume of water, the surrounding water is turned to very high pressure steam, and if there is a rigid attachment between the plate and the hull - since water is incomprehensible - but the hull is compressible, the vapor pressure blasts a hole in the hull. If it's attachment is weak (and you're very lucky), the plate may blow itself away from the boat - ripping somewhat smaller holes in the hull below the waterline where it was once attached. That's why I float a zinc plate a foot or so away from the hull behind the boat, suspended in the aft end of the engine well by its terminating wires alone. It just streams along behind the boat. I may lose the plate in a strike, but not the boat, and I've got spare plates (that cost $20 apiece). I admit that it would be with considerable trepidation - and many poured libations to Thor, that I would grab hold of the backstay chainplate to install a spare plate while underway after the previous plate just got blasted away. But lightning never strikes the same place twice, right? (Because that place has now been vaporized.)

I also object to making more holes in my hull below the waterline to mount a Dynaplate.

Wrapping up your loose electronics in anything conductive (foil, space blanket, etc.) is a good idea. I have a microwave oven on board (I ain't puttin' no propane inside my cabin!) and that's a great place to toss my spare handheld transceiver and GPS. I'm not sure about tripping the breakers, it's a coin-toss whether that would help or hurt by letting the positive side of the power supply float unimpeded rather than keeping everything connected to the low impedance path back to the battery. I'd be inclined to turn everything on instead. That's what we did at the broadcast transmitter: tower lights, building lights, and all the gear got powered up. We let the utility company, or the diesel generator when the power failed, absorb the hits. By the way, on the subject of surge suppression, on offshore oil rigs (talk about an extremely vulnerable spot to be during a thunderstorm!), they suppress lightning-produced voltage spikes on their AC power by connecting a bunch of 12 volt batteries in series. Two sets: each through opposite polarity steering diodes. The batteries had a voltage slightly lower than the peak voltage of the AC power. The AC keeps them partially charged, and when a spike occurs, the batteries absorb the spike as a sudden charge current. Ordinary automotive batteries (and boat batteries) will absorb hundreds of amps for a few tens of milliseconds without damage. Brute force. Works great! Cheap and effective.The folks at Exon-Mobil shared that little secret with me. They said they'd taken countless hits, and never had a battery blow up.

One thing I've noticed that puzzles me: I've never seen a single bit of marine life clinging to my zinc plate. Why doesn't anyone use zinc in anti-fouling paint - instead of copper? Because it dissolves too quickly?