Anti-Thunder system on boat

[Janis_59]

Hi! Hopefully I will not lift the already discussed theme(dead corpse kicking), but searcher shows not much of this was ever touched. So, I have 29 ft sailboat from about 1980+ when in Europe was no regulations about earthening of mast. Mast is 25x15 cm 11 m aluminum. As the last year I got in the violent not forcasted thunderstorm where flashing occurs each 2 seconds so near as 50 meters off to me, I am scared now. Thus I see the mast-top earthened spike is mandatory. But - that is exactly the point where the VHF antenna stays. Antenna has mandatory rule be no nearer than 0.94 meters off the ANY metallic parts (wavelength half). But the platform size is 25x15 and no more. How should I mount the peek? What have to be taller than antenna having 457 mm height. Should I construct some sort of side-keeper thus the two rods are scraping the sky, where antenna in center and thunder thing is meter aside, higher? Seems illogical and fancy. Or construct the antenna be inclinable or some sort of hinge, downward and upward, thus the thunder peek is only some 20 cm upper the mast top? Or use the antenna spike as streamer sharpness spitting charges against flash? But cable, in-spite it is rather heavy, have only 2 mm of central diameter, thus it is too small against existing recommendations. Or let I lower the antenna? Then the reach will be lost and then mast electronic shade will make a partial short-circuit to antenna field. That not good idea as well. So, what I should do before lift up that mast now??

 

[BlueBell]

Hi Janis_59,

Welcome to the Forum.

I think the first step is not to go out when thunder and lightning are possible.
The next step might be to install a grounding plate below the waterline connected to your mast by heavy, copper cable.
Also, you can use the search window (top right corner) to find answers to this same question in previous posts.
("lightning" may be a better keyword than "thunder" in your search)

BB

 

[Janis_59]

Hi! Blue Bell. Thanks for the attention, however the question was NOT about grounding plates, but about mast-top instead.

Surplus to this - if o know where one may fall, the soft pillow may be outspread that place. Storms are the thing what badly underlays the prognoses, that is only the habit that Windy.com shows the 0.8 meters waves but somewhere them are 2 meters, or shows the sunny weather with 0.4 meters but for 20 minutes overcomes drastic rain, thunder and wind for 30 m/s - and then after 20 minutes again really is the sunny nice weather and no waves. To guess for sure is never possible thus MUST be prepared for harmaggeddon if want be in the safe side.

And third, as I wrote above, I had carefully searched by that button before to print anything. There was no discussion previously about.

 

[fallguy]

Disconnect antenna before storm and run line away from or out toward water.

Add arrestor.

Lightning Protection For HF/UHF/VHF Antennas https://modernsurvivalblog.com/communications/antenna-lightning-protection/

 

[Janis_59]

Rather interesting discussion at the blog, however even author admits, that antenna is very bad lightning rod because the cable, and whatsomore the commenters. This is the system I use until today, just disconnect the plug and connect with the grounded schaumplast pontoons with wires immersed in water. Its sure better than nothing but known well it ought be better if apply the prescribed sharp rod with prescribed 5 mm diameter grounding wire.

P.S. actually, never understood clear why not to use the mast pipe itself for part of wire??

 

[BlueBell]

_59

I am so sorry to have misinterpreted your original post.

I found 3 pages of threads on lightning protection on boats on this forum.

Best of luck to you when lightning strikes!

BB

 

[Janis_59]

OK, Blue Bell, I shall search more carefully. Thanks for the care.

PS Do You are from the Greal Lakes area?? I have rather far relatives there, but never yet travelled to see them. Nice country, when I watch the NatGeo sequel about Canadian far-beat choffeurs. Enough snow to freeze anything . I am from climate where boating season begins at April by melting the ices and ends in November when first ices comes over. May is seeding/planting time, and December is for stable snow time, what releases at very end of March.

 

[rnlock]

Rather interesting discussion at the blog, however even author admits, that antenna is very bad lightning rod because the cable, and whatsomore the commenters. This is the system I use until today, just disconnect the plug and connect with the grounded schaumplast pontoons with wires immersed in water. Its sure better than nothing but known well it ought be better if apply the prescribed sharp rod with prescribed 5 mm diameter grounding wire.

P.S. actually, never understood clear why not to use the mast pipe itself for part of wire??

I don't know if there's a reason not to use it either, although you'd need a substantial conductor going through the hull to a conductive plate or something with a reasonable amount of area exposed to the water. Water is not a great conductor, which is why you need the big area. Your wires in the water may not have enough area unless they are quite long.

One thing to keep in mind is that you want the path to be as straight as possible. If you have a sufficiently sharp kink in it, you may get a side flash, because it creates impedance.

There are all sorts of other considerations. For instance, I think certain large metallic things have to be bonded together somehow.

I wonder if your VHF antenna (and radio) would have a chance of surviving even if the strike hit a lightning rod and followed a path straight to a big plate in the water. My guess is that that much current, adjacent to the antenna cable, would create electric and magnetic fields strong enough to induce large currents in the cable.

A guy I used to work with had a large yacht that was hit. Most of the electronics were destroyed. I didn't really understand why he couldn't go sailing without most of that stuff, but he didn't want to and missed most of a season of sailing. Fortunately, he wasn't on board at the time.

However, I'm no expert on this stuff, and I'm sure there are some pretty clear standards available. Plus, I seem to recall there were a few articles in Sail magazine that went into a fair amount of detail. But that was decades ago. I don't know if there's an archive.

BTW, I've done some diving in Lake Erie, but it was really boring. This is not a fault of Lake Erie, but of the project we were working on.

Further thought:
The only really effective anti-thunder system I can think of is to turn your boat into a submarine so you can't hear anything on the surface. ;-)

 

[Janis_59]

RE: rnLock
Firstly, I have no much questions about minimum demanded grounding plates area, it is well known value, and have experience what happens if to immerse the diy "mobile" plates - them very successfully tries to crush the hole into hull by the sharp corner . Thus, as the fixing copper plates to the keel contradicts the demand them be as possible near to the upper sea level and makes the problem with connecting wires (You`ll not intended to drill the underwater holes, seriously!); the same way fixing plates on the hull may easily result with fashionable carbonized hole in size of cow where water is flowing in to sweep all what have resisted to thunder EMP. Thus, yes, I believe the "mobile" electrodes is must to be, but not the plates. Or cylinders (santech copper pipe part with rather large diameter or much better - just the numerous cable wires hanging down from the perimetral alu bar over the boat deck. It already is there and cable may be used the brass wire-rope of something like 8 mm or 10 mm. Thus, to pass into right contact area, if the immersed part is 1 m long, the demanded count of such wires is about 5 (only!) in each side. In spite the direct hit by steel wire wouldnt get hole into hull, the hit energy is strongly diminished by air-bubble-polystyrene bobber keeping steel wire some 10 or 20 cm away of hull. Last time I checked such construction mechanics, it gave the very promising results. So, my question was solely for electronics - how to co-work antenna and arrestor

 

[Rumars]

I would make the air terminal (mast top spike) telescoping alongside the mast. Just insure that it has a good electrical contact with the mast exterior when raised. When it's raised it will interfere with the VHF antenna on transmit (pattern distortion), but you only raise it two situations, when you leave the boat (anchor, marina), or in a thunderstorm, and in both cases the radio is not in use.
Since you also plan for mobile grounding plates, it's not a problem to also pull a string to raise the air terminal.

 

[Janis_59]

RE: Rumars: Yep, similar was my initial idea to make antenna inclinable on the hinge and spring, when pull by rope that stays downright, when released it becomes upright. But then mechanical construction was more than the bit clumsy and sure the coaxial will suffer in the long run, even if spiralized some 3 to 5 turns. Then I meditated about inclinable arrestor, but stays written the copper cable to it ought to be at least 8 mm thick or better 10 mm. Thus the cable bending again is not the good deed. Sliding... OK, its not much simpler but still OK, however the cable problem persist. Coiled wire of course may amortize the half meter elongation, but then it makes the serious inductance to current, what for expected time-scale of lightning in few microseconds equal to Megahertz scale event, thus inductance plays the significant if not critical role. If to organize the contact via sliding contact, its clear what happens if lightning hit into arrestor. And specifism of marine arrestors systems different like on the land is that on land the probability to struck into arrestor is about 1: 10 000 000 whilst on the sea about 1:100. Thus marine arrestor must be capable to survive the smaller to average hit. However, probably, the inclinable arrestor having parallel plates contacture on the hinge-screw may work even at megaampere scale (once in the life-span). Shall meditate about it, when will come one sleepless night. So, thanks for idea to shift the arrestor instead of antenna.

 

[Rumars]

I see two possibilities, folding or sliding.

Folding: around 30-50cm below the head of the mast you rivet a hinge, made out of two L plates. Necessarily the pivot point will be about 2cm from the mast wall. On the entire lenght between hinge and masttop you rivet a distance piece to bridge the gap between mast and rod. This can be a half tube and spacer, or a solid piece milled (can also be done with hand tools and time) to match the contours of the mast and rod. This is the primary electrical connection path, a good fit is preferred. You use a low strech line to keep the rod pressed against this spacer when in the up position. It won't be as tight as a screwed connection, but this doesn't matter with megavolts and megaamperes.
Below the hinge you have the same arrangement, one or two short plastic spacers and a line, this will keep the rod from banging on the mast when folded.

Sliding:
You need a track, this can be milled or made from two flat bars (a narrower one riveted under a wider one) or a commercial one from a genoa or traveler. The car is made from a piece of square tubing in wich you cut a slot, or bent from sheet. The rod gets a flat on one side, and is riveted to the car. Between car and track you install a conducting shoe made from graphite, for that you use several electric motor brushes (cheap, buy some reserves). The car needs removable endcaps so the brushes doesn't escape. Everything gets coated with electric conducting grease. The track has two stops, the lower one a simple L, the top one is made from a pice of tubing in wich the rod can slide, grease it.
This is a one line affair, the rod should slide down under its own weight. You could make it a two line thing and have a very stiff friction fit, then you need to regularly shim or exchange the carbon brushes. This is an option if you normally remove the mast for winter storage, you could do it every spring.
There are other possibilities for a sliding arrangement, for example a tube with a slot riveted to the mast into wich the rod can slide, but you need to have a good fit between tube inside and rod, this usually involves machining.

All of the above constructions I would make from Al, with the actual air terminal (arrestor) beeing a pipe with a riveted on solid tip, ground to a point.

 

[Janis_59]

OK, then I have one at least, the similarly thinking captain. Seems I should go this way.