Smith-Root ELECTROFISHING BOATS, User Manual, Page: 37 / 53

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USER'S MANUAL
LIGHTNING AND THUNDERSTORM
PROTECTION fOR SAILBOATS, POWER
BOATS, SMALL BOATS AND SHIPS.
1. GENERAL PRINCIPLES
Successful protection of persons and watercraft from
lightning is dependent upon a combination of proper design
and maintenance of equipment, and on crew behavior.
Proper design is covered in this and following sections.
Maintenance of equipment and personnel behavior is also
covered. In view of the wide variation in structural design
of boats, specific recommendations cannot be made for all
cases. However, basic guidelines should be considered
and used in designing and installing a lightning protection
system for any given craft.
A grounded conductor or lightning protective mast will
generally divert itself to direct hits which might otherwise
fall within a cone-shaped space, the apex of which is the top
of the conductor or lightning protective mast and the base is
a circle at the surface of the water having a radius related to
the height. For a mast height not exceeding 50 ft., (15 m)
above the water, this radius is approximately equal to the
mast height.
To provide an adequately grounded conductor or lightning
protective mast, the entire circuit from the top of the mast
to the ground should have a conductivity not less than that
of a No.8 AWG copper conductor and the path to ground
followed by the conductor should be essentially straight.
To remove all known risk of melting the conductor while
carrying lightning current, conductivity equal to No.6 AWG
or no. 4 AWG copper would be necessary. However, the risk
in using No.8 AWG is considered adequately small in the
applications under consideration, and in many cases will be
mitigated by the presence of electrically paralleling stays.
This statement should not be interpreted as permitting the
use of conductors of conductivity less than that of No. 8
AWG copper.
If there are metal objects of considerable size within
a few feet of the grounding conductor, there will be a
strong tendency for sparks or sideflashes to jump from the
grounding conductor to the metal object at the closest point.
To prevent damage from such sideflashes, an interconnecting
conductor at least equal to no. 8 AWG copper should be
provided at all places where they are likely to occur. Large
metallic objects that are not part of the electrical system of
the boat and that are not already grounded due to their own
functional or other requirements may be grounded to the
ground plate, provided that it is not practical to interconnect
with the lightning conductor or bonding systems.
Lightning protection provisions are quite likely to receive
scant attention after installation and therefore their
composition and assembly should be strong and materials
used should be highly resistant to corrosion.
2 INSTALLATION RECOMMENdATIONS
Lightning Protective Mast. A lightning protective mast
should be of adequate height and should be mechanically
strong in order to withstand exposure to use and weather.
If the mast is of nonconducting material, the associated
lightning or grounded conductor should be essentially
straight, securely fastened to the mast, should extend at least
6 in. (150 mm) above the mast, should preferably terminate
in a receiving point, should be led as directly as practical to
the grounding connection.
Radio Antenna. A radio antenna may serve as a lightning
protective mast provided it has conductivity equivalent to
No. 8 AWG copper and is equipped with lightning arresters,
lightning protective gaps, or means for grounding during
electrical storms. The grounding of metal rod-type radio
antennas constitutes sufficient protection for wooden boats,
without masts or spars, provided the following conditions
are met:
The antenna and all conductors in the grounding circuit of
the antenna have a conductivity equivalent to No.8 AWG
copper.
The top of the antenna is not more than 50 ft. (15m) above
the water, and a line drawn from the top of the antenna
downward toward the water at an angle of 45 degrees to the
vertical does not intercept any part of the boat.
LIGHTNING PROTECTION