[C320-list] Lightning

[Allan Field]

Tom - Practical Sailor has several articles on their website that speak to
lightning protection. You would need a login and password to access. But
following is just one article with a recommendation at the end that might
help.

Allan S. Field
Sea Shadow - C387, #103 (formerly C320, #808)
Columbia, MD

Most boat owners have only the vaguest idea of what is involved in
protecting their boats from lightning damage. Many believe that their boats
are already protected by the boats grounding system. Most are wrong.

Just because your boat may be bonded with heavy copper conductors
connecting the masses of metal in the boat doesnt mean that it is protected
against lightning. A bonding system may be a part of a lightning protection
system, but bonding itself offers no protection to the boat unless a good,
direct path to ground is part of the system.

While neither aluminum nor stainless steel is an outstanding electrical
conductor, the large cross-sectional area of both the mast and the rigging
provide adequate conductivity for lightning protection. The trick, however,
is getting the electricity from the mast and rigging to the water.

The straighter the path is from conductor (mast and rigging) to ground, the
less likely are potentially dangerous side flashes. Put simply, side
flashes are miniature lightning bolts which leap from the surface of the
conductor to adjacent metal masses due to the difference in electrical
potential between the charged conductor and the near by mass of metal.
Ideally, therefore, the path from the bottom of the mast and rigging to
ground would be absolutely vertical. In practice, this is rarely achieved.

If the boat has an external metal keel, the mast and standing rigging is
frequently grounded to a keelbolt. There are pitfalls to this method.
First, the connection between the bottom of the mast and rigging to the
keelbolt must be highly conductive. ABYC (American Boat and Yacht Council)
standard TE-4 for lightning protection systems require that these secondary
conductors have a conductivity at least equal to that of AWG #6
copper-strand cable. There is no drawback to using an even larger conductor.

Connecting the short conductor to the mast and keelbolt presents some
problems. A crimp eye can be used on the end that is to be attached to the
mast, but you may have to fabricate a larger eye for attachment to the
keelbolt. This can be made from sheet copper. Soldering the connections is
not recommended, since the heat generated in a lightning strike could melt
the solder.

Then you have to face up to a basic problem. Your mast is aluminum, yet
youre connecting it to ground with a copper cable. Everyone knows that
aluminum and copper are not galvanically compatible, so whats the solution?
While it will not eliminate corrosion, a stainless steel washer placed
between the copper cables end fitting and the aluminum mast will at least
retard it. But this connection is going to require yearly examination to
make sure that a hole isn’t being eaten through the mast. In addition, of
course, the process of corrosion creates wonderful aluminum oxide
byproducts, which have very low conductivity. The aluminum oxide may reduce
conductivity to the point where your theoretical attachment to ground is in
fact non-existent. Once again, disassembling the connection and cleaning it
yearly are essential to maintain conductivity. Constant attention to all
the conductor connections is essential in any grounding system, whether its
for lightning protection or grounding of the electrical system.

For more information on how to best protect your boat from lightning
strikes, purchase Nigel Calder’s “Boatowner’s Mechanical & Electrical Manual
<https://www.practical-sailor.com/subscribe/main.html?t=Ad1&s=P_Waypoints050813F#books>”
from *Practical Sailor*.

On Sun, Dec 13, 2020 at 10:51 AM Tom Grass <tgrass462 at gmail.com> wrote:

> Wondering about lightning protection on Catalina 320 boats?  I don't
> believe they come grounded (mast to keel) from the factory - wondering what
> the members of this forum have done in an attempt to minimize the impact of
> a possible lightning strike?
>
> Also what is the collective opinion of installing a Forespar Performance
> Products Forespar Lightning Master™ - Static Dissipater
> on your mast?  We're planning on sailing down to the Chesapeake Bay and
> perhaps to the Bahamas in 2021 - just preparing in advance.
>
> Thanks,
>
> Tom and Tracy Grass
> Bucket List
> 2008 Catalina 320 MK II
>