Dennis contributed:  The bottom line is that the only gear that will likely
survive is not connected to either the electrical supply OR the ground
system...  Any connection will allow voltage to build up on the equipment
and then jump to something near by..

Scott thankfully asks:  I'm currently installing $30k in backup nav and
entertainment gear.  It will be installed exactly as you describe, I will
make certain each component is completely disconnected from both power and
ground.

Do you have any recommendations on good connector technology to achieve
this?  I'm visualizing a bulkhead behind a panel where the various
components source their power and antenna leads.  After gracefully shutting
down the gear I will gain access to the panel and physically remove the
power and other leads.  A connector that provides keyed, reliable connection
in a small package is desirable.

Finally, what do you think of electro optical isolators for the GPS and
other serial interfaces?  Easier to simply convert to RS232 physical
connectors and disconnect?  And finally, component or composite video?

Thanks, Scott Bulger, Alanui, N40II, Seattle WA

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

John advised:  I would suggest that will NOT include lightning even if it is
disconnected completely.

thank you John,

It sounds like even if I remove the power, ground and antenna connections,
stray current will damage the components through what sounds to me like
"induction".  I'd hoped that an air gap of inches would have prevented
conduction, but the forces are work here sound insurmountable.  I'm still
pulling the wires for the gear and I have not abandon my idea of making a
bulkhead that can isolate all the gear, it all goes the same place for power
anyway, it's just a simple step to put quick disconnect fittings at the end.
I'll consider this in light of your advice.  Again, thank you!  Scott

What you intend to do cannot hurt. There is probably an infinite variety of
strikes with different proximity and different outcomes. You do your best
under your concept of what's appropriate. In the Army, we disconnected our
antennas as a matter of personnel safety. Since power sources and grounds
were discrete, you could disconnect your radio completely. I had
disconnected my inverted "L" antennas just before two massive strikes about
40 yards away on a hilltop. The radio was unaffected even though I forgot to
disconnect the ground plane. This was a WWII/Korean War era radio. Yes,
lightning does strike in the same place multiple times.

If the strike is not direct, you might survive with some gear intact. In
reading the specs for a larger Nordhavn, I see that they use a grounded
fuzzy metal dissipater to lessen the likelihood of a strike. You might wish
to determine what method, if any, they used on your boat.

Lightning protection and bonding are both controversial subjects with
experts on both sides. You have to pick your theory.

Ron Rogers
----- Original Message -----
From: "Scott E. Bulger" scottebulger@comcast.net

| John advised:  I would suggest that will NOT include lightning even if it
is
| disconnected completely.
|
| thank you John,
|
| It sounds like even if I remove the power, ground and antenna connections,
| stray current will damage the components through what sounds to me like
| "induction".  I'd hoped that an air gap of inches would have prevented
| conduction, but the forces are work here sound insurmountable.  I'm still
| pulling the wires for the gear and I have not abandon my idea of making a
| bulkhead that can isolate all the gear, it all goes the same place for
power
| anyway, it's just a simple step to put quick disconnect fittings at the
end.
| I'll consider this in light of your advice.  Again, thank you!  Scott