a blue cast on rigging signifies a lightning strike

[vpbarkley]

I believed my boat was struck by lightning prior to purchasing her. Most of the electronics were dead. But, otherwise I had no actual evidence of a strike.

I had riggers on my boat last week. I asked if they would check the rig for any signs of a lightning strike while they were aloft.

They reported the VHF antenna and wind instruments were still there. But they noticed the rigging had a blue cast to it.

I checked with my surveyor and she verified that stainless rigging having a blue cast is indeed a sign of a lightning strike.

I wanted to pass this information along to fellow cruisers. I was previously unaware of this indication of a lightning strike.

[Knotical]

Originally Posted by vpbarkley

But they noticed the rigging had a blue cast to it.

On stainless stays/shrouds or aluminum mast? Did the surveyor say how it forms?

[Alan Mighty]

Originally Posted by vpbarkley

I checked with my surveyor and she verified that stainless rigging having a blue cast is indeed a sign of a lightning strike.

Most interesting. Thanks VPB for the information.

I used to ride a motorcycle with stainless steel exhaust headers and pipes. A blue tint of the chromium oxide layer in that setting is called 'heat tint' and just indicates the temperature of the exhaust gases.

The same 'heat tint' shows up on some stainless steel cookware.

In the case of exhaust headers and cookware, the 'heat tint' does not affect performance.

Does scientific evidence exist to suggest that stainless steel wire rope, terminals, or other fittings are compromised in strength if they show heat tint?

[vpbarkley]

The oxide layer thickness on stainless steel increases when heated in air, giving coloration.

At a constant temperature this starts to occur at ~ 500 degrees F.

If heated to a much higher temperature but for only a fraction of a second you get the same reaction.

Lightning travels along the skin of conductors, directly heating the surface.

[Alan Mighty]

Originally Posted by Alan Mighty

A blue tint of the chromium oxide layer in that setting is called 'heat tint' and just indicates the temperature of the exhaust gases.

Searching for 'heat tint' comes up with a handy guide to what temperature the colours of heat tint mean and how they form.

See: https://cougartron.com/blog/heat-tint-removal/

[vpbarkley]

I suspect the strength of the stainless wire rope is not seriously effected. But, check for welding at the fittings. This shows as dark discoloration with pitting and cracking.

[JohannDW]

I know for a fact that my boat took a direct strike a few years ago because almost everything electric and electronic had to be replaced. There was absolutely no 'blue cast' to any of the rigging we replaced, but the radio antenna and the Windex as well as the wind speed instrument were all vaporised- nonexistent. So, if the antenna and masthead fittings are all there, then I do not think it could have been any significant type of lightning strike.

[NPCampbell]

Heating austenitic steels like 316 to 400C or higher will often soften them.

[vpbarkley]

Johann,

So you're saying it was just a little, insignificant strike; just enough to take out the VHF radio, auto pilot, chart plotter, wind instruments, alternator, regulator, water maker lift pump, inverter, air conditioner control board and satellite TV receiver. And, while it visually did not damaged the VHF antenna and mast top wind instruments, it did damage the mast cables.

[barnakiel]

Originally Posted by JohannDW

I know for a fact that my boat took a direct strike a few years ago because almost everything electric and electronic had to be replaced. There was absolutely no 'blue cast' to any of the rigging we replaced, but the radio antenna and the Windex as well as the wind speed instrument were all vaporised- nonexistent. So, if the antenna and masthead fittings are all there, then I do not think it could have been any significant type of lightning strike.

What was your "anti strike" attitude back then?


Was rig grounded in any way (special copper cable to the keel, etc?)


Any damage to thru-hulls or similar?


thanks.


barnakiel

[n5ama]

Originally Posted by vpbarkley

Johann,

So you're saying it was just a little, insignificant strike; just enough to take out the VHF radio, auto pilot, chart plotter, wind instruments, alternator, regulator, water maker lift pump, inverter, air conditioner control board and satellite TV receiver. And, while it visually did not damaged the VHF antenna and mast top wind instruments, it did damage the mast cables.

In my experience a non direct hit can take those items out.

A direct hit Will not only take out all the solid state items but will also vaporize cables, power lines, ground lines and most anything conductive in the area and it doesn’t necessarily have to be connected.
The ground cables can be destroyed if they have some resistance or their connection to ground Has resistance.

So yes, a “ little insignificant strike” can do that level of damage.

[CassidyNZ]

I must say that, looking at the VHF antenna on my boat, it’s hard to believe that enough current to fry all electrics on board and “heat tint” the rig would not damage the antenna. I would have thought a VHF antenna would simply melt. Interesting.

It is of course possible that the previous owner could have replaced the masthead gear but why would you if everything in the boat that is connected to it is dead?

[vpbarkley]

The boat has a deck stepped mast. There is a good sized copper cable connecting the port chainplate to a keel bolt. The boat has a cast iron keel.

Possibly the mast itself is not connected to ground except through the mast top instruments while the rigging is definitely well connected to ground.

I suspect that keel stepped (aluminum) masts provide a superior, more direct path to ground than do deck stepped masts.

[boatpoker]

The only boat within 1 mile. The lightning hit the water about 30' off our starboard side and boiled a huge hole in the lake.

Why didn't it hit us ? ... because 200,000 amps travelling at 300,000,000 meters per second does what ever the hell it wants.

Lightning and boats on water are completely unpredictable.

I've seen boats with no electronic or electrical damage but with thousands pf pinholes in the hull from side flashes. No one can predict what will happen when lightning strikes.

Flash heating of ss rigging can certainly cause bluing

[n5ama]

Originally Posted by CassidyNZ

I must say that, looking at the VHF antenna on my boat, it’s hard to believe that enough current to fry all electrics on board and “heat tint” the rig would not damage the antenna. I would have thought a VHF antenna would simply melt. Interesting.

It is of course possible that the previous owner could have replaced the masthead gear but why would you if everything in the boat that is connected to it is dead?

A lot of modern electronics can be damaged with just the static discharge on your body when working on it. Ground straps connected from the wrist to the device is frequently needed before a service person works with the discrete components to dissipate the static from the body before touching the device.

This obviously isn’t a problem once the device is assembled and ready for use. It doesn’t take a large amount of power to “fry” these things, just high enough voltage at low current will do it. The voltage in the static discharge on your body can be fairly high.

The coil in your antenna is fairly robust and can take much more voltage and current without damage.