What is this mystery electrical accessory?

[chris95040]

Originally Posted by AlanR

If struck by lightning, it would instantly evaporate, the wire is so thin.

People love to make this claim, yet it never seems to happen to rigging wire!

Have you ever heard anyone say ‘and after the strike, my rigging evaporated and my mast fell over’?

[Wotname]

Originally Posted by MarkusK

I am glad I asked and happy to see the replies.

The approx 8" x 8" metal plate is fairly light-weight, but not sure of composition. How to verify if it is zinc? Or aluminum? It is definitely not copper or steel.

I ASSume the cable is copper but will give it a scrape to be sure.

The previous-previous owner was an engineer...who knows what he was tinkering with?

If it "feels" light, it is likely to to be Al; Zn would "feel" heavy.

Common Al alloys are also soft, Zn not so much.

You could determine it's volume and it's weight and work backwards from an SG table like this Solids and Metals - Specific Gravity

[Bleemus]

It's aluminium. Zinc would be heavy. Aluminium is a good conductor. Lightning protection.

[hzcruiser]

Originally Posted by AlanR

If struck by lightning, it would instantly evaporate, the wire is so thin.

So what size wire do you think would be needed?

[Bradwithnoboat]

Originally Posted by chris95040

People love to make this claim, yet it never seems to happen to rigging wire!

Have you ever heard anyone say ‘and after the strike, my rigging evaporated and my mast fell over’?

I know I'm new here and don't have a boat but the rigging question is probably simple to answer. The electrical resistance between the rigging and true ground would be very high, so despite there being a lightning strike, the current flow would be minimal - I = V/R - If 'R' is high, the 'I' is low (relatively speaking).

One of the places I used to work had some large wired antenna arrays with copper spark-gap grounding systems. The copper electrode wasn't wire, it was tube/rod, about 15mm in diameter. They had some mounted specimens that showed the damage caused by lightning strikes on the antennae. Partially vaporised is how I would describe it.

The other variable would be whether the rigging was directly struck, or just an induced level of voltage (proximity charge) was the source of electricity.

Sorry for the rambling response but I felt the need to comment.

[dfelsent]

Or magnesium. Used for electrolysis protection in fresh water.

[chris95040]

Originally Posted by Bradwithnoboat

I know I'm new here and don't have a boat but the rigging question is probably simple to answer. The electrical resistance between the rigging and true ground would be very high, so despite there being a lightning strike, the current flow would be minimal - I = V/R - If 'R' is high, the 'I' is low (relatively speaking).

One of the places I used to work had some large wired antenna arrays with copper spark-gap grounding systems. The copper electrode wasn't wire, it was tube/rod, about 15mm in diameter. They had some mounted specimens that showed the damage caused by lightning strikes on the antennae. Partially vaporised is how I would describe it.

The other variable would be whether the rigging was directly struck, or just an induced level of voltage (proximity charge) was the source of electricity.

Sorry for the rambling response but I felt the need to comment.

Many (most?) boats ground their rigging. While stainless rigging is not as good a conductor as copper, the resistance to ground is not what would typically be called ‘high’.

And even still, most of the time the subject of copper conductors ‘vaporizing’ comes up (including the post I was responding to), it is in regard to a series connection where rigging is provided a path to ground via copper conductor. The subject of this thread was a device that some were speculating was used to attach to rigging and throw overboard. This series connection means that the copper conductor will see no more current than what flowed through the rigging on its way to ground. If the copper conductor were to ‘vaporize’, why didn’t the rigging that carried that very same current?

Google ‘kirkoffs current law’, its basically your first stop in understanding electricity. While your observation that copper is a superior conductor to typical rigging materials is correct, it doesn’t really have any impact on whats being discussed.

[Bradwithnoboat]

Not sure what happened to the beginning sentance of this reply.....

I wasn't aware that the norm is for rigging to be grounded.
As to Kirchoff's laws, I learnt those some 35 years ago in my training. My mistake for responding to an open discussion where my mechanical knowledge of the configuration of ships rigging is lacking.

[Wotname]

Originally Posted by Bradwithnoboat

Not sure what happened to the beginning sentance of this reply.....

I wasn't aware that the norm is for rigging to be grounded.
As to Kirchoff's laws, I learnt those some 35 years ago in my training. My mistake for responding to an open discussion where my mechanical knowledge of the configuration of ships rigging is lacking.

Bradwithnoboat, welcome aboard CF, the crewmates here are generally fine fellows but they can be a bit rambunctious at times.

For the record there are many many boats around the world that do not have their rigging grounded just as there are many many with the rig grounded in some form or another (and often inadequately IMO).

If you want to get involved with some controversial threads, find some about lightning mitigation, lots of different opinions, occasional facts and very occasionally, some serious electrical theory discussion .

[GordMay]

Greetings and welcome aboard the CF, Bradwithnoboat.

[AlanR]

A lightning strike would prefer to run down the aluminium mast. At 100,000 volts or so, it would punch a hole in the bottom of the boat, to reach ground. It does not like to turn corners, as they create inductance, so the lightning will tend to jump off the conductor and find another route at these points.

The current will be in the order of thousands of Amps. Look at the lightning conductor on the spire of your local church. Probably an inch by a quarter inch of solid copper, to handle the current.

Most lightning damage to equipment is caused by induced voltages from a strike a few miles away. The mast and rigging survive, but electrical equipment on board is wrecked, by the voltage, not the current.

I have seen a skipper wrap several turns of anchor chain around the foot of the mast, at deck level, and dangle several loops over the side, into the water. Even if the chain is welded into one piece, it's better than the mast exiting the boat through the bottom.

Thousands of Amps anccompanied by thousands of Volts behave differently to your household electricity, even if they do follow the same rules.

73s

Alan

In temperate climates, lightning STRIKES are rare.

[stormalong]

I stick by my post that it is for measuring stray currents in a marina that could cause significant electrolysis damage to underwater metal.

A lightening strike would vaporize that thing.

[chris95040]

Originally Posted by AlanR

A lightning strike would prefer to run down the aluminium mast. At 100,000 volts or so, it would punch a hole in the bottom of the boat, to reach ground. It does not like to turn corners, as they create inductance, so the lightning will tend to jump off the conductor and find another route at these points.

The current will be in the order of thousands of Amps. Look at the lightning conductor on the spire of your local church. Probably an inch by a quarter inch of solid copper, to handle the current.

Most lightning damage to equipment is caused by induced voltages from a strike a few miles away. The mast and rigging survive, but electrical equipment on board is wrecked, by the voltage, not the current.

I have seen a skipper wrap several turns of anchor chain around the foot of the mast, at deck level, and dangle several loops over the side, into the water. Even if the chain is welded into one piece, it's better than the mast exiting the boat through the bottom.

Thousands of Amps anccompanied by thousands of Volts behave differently to your household electricity, even if they do follow the same rules.

73s

Alan

In temperate climates, lightning STRIKES are rare.

Many sailboats are struck by lightning at the masthead as it seeks a path to ground. What percentage of them end up with a hole punched through the hull?

[AlanR]

[QUOTE=chris95040;2636657]Many sailboats are struck by lightning at the masthead as it seeks a path to ground. What percentage of them end up with a hole punched through the hull?[/QUOTE

I think many reports fail to differentiate between a lightning strike and "damage caused by lightning."

Have you seen the damage caused by a lightning strike on an unprotected chimney. It's like a bomb went off. I believe that many (most) reports are of lightning damage from induced current, and so current flows through equipment where these high voltages break down insulation, wrecking the equipment, and track to earth through through a metal hull or the sacrificial anode. Still very much less current than the original strike.

Induced current is the same effect that causes a transformer to work. The lightning's huge current creates a huge magnetic field, which induces currents in any conductor within that field. The crackles you can often hear in a medium wave broadcast band radio are from lightning strikes perhaps thousands of miles away. You can not see the flash or hear the thunder, only hear the electrical pulse, through your radio.

A real strike had a huge current, causes explosions, fires, splits trees and kills people standing nearby. That is, unless there is a proper lightning conductor, like the one on a church spire, or several lengths of anchor chain. Not the little wire in the unknown piece of equipment we are discussing. That would most certainly provide no protection against a direct strike.

73's

[Franziska]

Here a first hand story of a strike:

http://www.sailingcatamarans.com/ind...n-eclipse-2003