[PUP] FW: Lightning preparedness

[John Harris]

Scott,

I wish you good fortune with backup Nav and entertainment gear, having a 
second set will protect you from many failures but I would suggest that will 
NOT include lightning even if it is disconnected completely.

The electrical equipment and lightning issue is based on the following 
analysis.

1. The lightning strike is produced by a very large "spark - if you wish" 
that is millions of volts in potential.

2. The large "capacitor" discharges - at least in part - by ionizing the air 
to a "(often)  sharp high object - for example your mast.

3. The electrical energy is dissipated during several very very high current 
surges down the mast to ground - think in the 100,000 amp range

4. These VERY large current produces a large magnet field the engulfs the 
whole boat - this field is generally not damaging to anything except 
"conductors".

5. All of your nav and entertainment equipment contains electrical 
conductors, many of them and only stand a few or a few dozen volts before 
they fail - that includes all the semiconductors in the equipment.

6. Given that even some of the semiconductors in the nav and entertainment 
equipment fail the equipment is generally far beyond repair.

7. The only protection that I know for this problem is a "Faraday box" which 
with provide a near complete blockage of the magnet field reaching the 
equipment.

I hope this is helpful and not too disappointing.

John Harris
World Odd @ Sea
N-4657