What Happens to Marine Life When Lightning Strikes Conductive Sea Water?

[saddlestone-man]

TL;DR

What happens from a physics/chemistry point of view when lightning strikes the sea?

Hello All

Has it ever been observed or modeled from a physics or chemistry point of view what happens when a lightning strike hits conductive sea water?

Because of the high current density and presumably high temperature, does the sea water dissociate into hydrogen and oxygen, and then recombine into water, resulting in an explosion?

best regards ... Stef

 

[Baluncore]

Since water has a high dielectric constant, it will take a relatively long time for the current to penetrate any depth of sea water. The current will therefore spread out through the surface air, covering a large surface area of sea water.

The current density will therefor be much lower than the current density in the ionised air. The resistance of salt water is also much lower than the ionised air, so little energy will be dissipated in the water.

I have watched lightning striking the sea surface nearby, and have not seen a jet of steam. I would expect a gentle depression of the surface due to the pressure wave from the expanding air in the strike above.

 

[davenn]

Summary:: What happens from a physics/chemistry point of view when lightning strikes the sea?

does the sea water dissociate into hydrogen and oxygen, and then recombine into water, resulting in an explosion?

Never seen an explosion yet in either sea or lake strikes. In fact it's a relatively quiet affair.

The neatest thing that can be seen is when there are the streamers coming up out of the water that didnt connect with the downcoming leader

Generic images

 

[saddlestone-man]

They are fantastic pictures! I wonder if you get dead/stunned fish from the electrical field and pressure wave from the strikes?

best regards .. Stef

 

[berkeman]

I wonder if you get dead/stunned fish from the electrical field and pressure wave from the strikes?

Looks like as long as the fish are a little under the water they are usually okay. Humans swimming on the surface -- not so much...

https://www.weather.gov/safety/lightning-fish

 

[snorkack]

Looks like as long as the fish are a little under the water they are usually okay. Humans swimming on the surface -- not so much...

https://www.weather.gov/safety/lightning-fish

Fish can stay under water because they can breathe water. Us amniotes must reach surface to breathe air.
Are whales, seals, hippopotami, crocodiles, turtles and other such aquatic amniotes commonly thunderstruck when surfacing?

 

[Baluncore]

Are whales, seals, hippopotami, crocodiles, turtles and other such aquatic amniotes commonly thunderstruck when surfacing?

No, it is very uncommon.

Lightning strikes at sea are rare compared with strikes on or near land. Whales and seals will be struck sometimes, and it is possible that some will be killed. A whale is covered in a layer of conductive salt water so the lightning current will spread out over a large area and so not burn their skin. People are burnt by the surface currents because they have dry skin. The whale also has a thick layer of insulation in the form of fat that should protect them.

So long as hippos and crocs are in the water, and near the bank, they will be protected to some extent by the higher vegetation. Maybe a couple will be killed every decade, but there is always something that will eat that evidence. Have you never wondered why hippos and crocs keep a low profile, with just their eyes above the surface? Do they dive during thunderstorms, or do they ride it out on the surface?

https://www.abc.net.au/news/2018-09-17/drought-impacts-croc-mating/10247516

 

[Baluncore]

Google; marine mammals killed by lightning

“What about animals at the surface like whales and dolphins?”
But no reference to the original work reported.
https://www.tidaltao.com/blog/107-blog-news/276-why-dont-fish-die-when-lightning-strikes-the-sea

“For the first time, lightning is known to have killed a marine mammal”
http://www.bbc.com/earth/story/20150813-sea-lions-hit-by-lightning
But they were on land at the time.

 

[tech99]

I have occasionally been in my little sailing boat and a thunder storm has occurred. Just hope that statistically it is unlikely to be struck. It is not usually practicable to get out of the storm. On one occasion, I noticed a metal pole on top of a nearby sand dune; it had been there for many years and there was no sign of a strike even under close study. I have a wooden mast, but I do carry some long copper cables to dangle in the sea and connect to the shrouds in the slight hope it might protect me. If possible I try to position myself at night fairly near a vessel with a very high mast in the hope of obtaining protection.

 

[anorlunda]

An animal floating on the surface of the sea is surrounded by salt water. Salt water is conductive; I suspect more conductive than the body of the animal. Why then should surface currents prefer to go through the body rather than around it?

One could attempt to make a model of the situation given various resistivities, surface areas, and lengths, but it would be very complex. On the other hand, it would be pretty straightforward to measure it by experiment using animal cadavers. My guess is that navies around the world have done the experiments and the results sit somewhere on the book shelves.

 

[hutchphd]

I do carry some long copper cables to dangle in the sea and connect to the shroud

My guess is that a dangly cable on the shrouds and stays might make a big difference. You probably want them all grounded (or "watered") . Anyone have better knowledge?

 

[anorlunda]

Here we go. Lightning effects is a perennial favorite topic on PF.

My guess is that a dangly cable on the shrouds and stays might make a big difference. You probably want them all grounded (or "watered") . Anyone have better knowledge?

Yeah. I used to be up to my eyeballs in that topic as a full-time cruiser living on a boat 24x7x365. When you do that, there is no chance of getting off the boat to hide from storms.

The answer is that it is one of those topics where every experiences expert has his/her own opinion about small boat lightning protection.

The metal mast, not the side stays, is the subject of most focus. I grounded my deck stepped mast to a Dynaplate grounding plate mounted on the outside of my hull below the water line. A second Dynaplate grounded the engine. Some experts writing articles in boating magazines swear by that, and others say that is it useless.

I also put a plastic conduit around the cable connecting the mast and the plate to prevent molten copper from spraying around the cabin full of people.

Despite that, one strike wiped out my electronics (including hand-held devices). But I blame that on EMP, not through flow of current. Our friends had a strike that blew a 40 cm hole in their hull (above the water line, thank goodness). Another case of 3 men hiding from a storm in a boat inside lock 9 of the Erie Canal. Lightning blew multiple holes in the cabin roof and the hull below and the boat immediately sunk in the lock. The men weren't hurt. EMP can't make holes in fiberglass.

Here's the official word from ABYC standards.

A good lightning protective system ensures that all large masses of metal are electrically connected. This purpose should not be confused with that of the vessel's basic bonding system. A properly installed and isolated bonding system is there to provide a low resistance electrical path to reduce electrolytic corrosion and as a measure of personal protection if there is an electrical fault in the boat's AC/DC electrical systems.

If your sailboat is a vessel with an aluminum mast you have the starting point of a well-grounded lightning rod. This will provide a zone of protection for a radius around its base equal to the height of the lightning rod. Due to some vessels overall length, it may be necessary to install another lightning rod to encompass any areas that do not fall within the zone of protection. Don't forget that the mast itself must be physically bonded or connected through to the common ground - one of the keel bolts or if a encapsulated keel, to the grounding plate, in order to provide optimum protection.

The apex of the rod should be a minimum of six inches above any masthead device. The end should be sharpened to a point. The base of the mast or the mast step if metal, should be connected to a keel bolt on externally ballasted vessels. The preferred wire gauge is No. 6 or even better, #4AWG stranded copper. In no case should such a connection be made to a vessel with internal ballast. The result could be a hole blown through the bottom of the hull. Boats with internal ballast should have a copper ground plate of at least one square foot in size installed externally on the hull bottom. The grounding wire should then be connected to the ground plate.

All wire conductors should be kept as straight as possible. All large metal objects above and below decks should also be electrically tied into the lightning ground conductor. This is a precaution against side flashes. Large metal objects include shrouds, chainplates, toe rails, sail tracks, winches, steering wheels, and bow and stern pulpits. These items can be tied into the ground conductor wire by a minimum #8AWG stranded copper gauge wire, or connected directly to the hull ground terminus.

 

[DBO]

As a long time sailor who lives in FL and am frequently in thunderstorms, I am very careful about it. A lone sailboat under s t-storm has a pretty good chance of getting hit (I forget the numbers). A Dynaplate will not work. You need an actual copper plate. Mine is 2' X 2' X .025"connected with crimped, bolted and soldered 00 gauge tinned copper cable. Other end has a welding clamp to be connected to the mast up kigh above the boom so as to minimize bends in the cable.
Ive modified this rig so that it can be used while underway. I use floating pool noodles slid over the 00 gauge cable and I stream it astern.
I was thinking of selling my lightning ground but I seem to be the only person paranoid enough to actually use it.
BTW, there is no good way to prevent a strike, all you can do is dissipate one.
I don't think EMP blows holes in boats, it is done by direct heating of moisture in the fiberglass laminate by thousands of amps

 

[berkeman]

I don't think EMP blows holes in boats, it is done by direct heating of moisture in the fiberglass laminate by thousands of amps

I think @anorlunda was just saying that he thought it was the associated EMP that took our his electronics...

one strike wiped out my electronics (including hand-held devices). But I blame that on EMP, not through flow of current.

 

[256bits]

An animal floating on the surface of the sea is surrounded by salt water. Salt water is conductive; I suspect more conductive than the body of the animal. Why then should surface currents prefer to go through the body rather than around it?

Probably for the same reason one doesn't get out of a car that is hit with a live wire.
The voltage decrease the farther away from the vehicle, and even thought the ground can be highly conductive, the voltage between steps can put you at risk.
Although, for a live wire, the electric potential is continuous in time, so there is some difference.
Smaller length animals in the water near the strike should be at less of a risk.