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GordMay · 29-06-2008, 03:10

Lightning Rods (Air Terminals) are placed on top of sailboat masts, not to dissipate any accumulated static charge, but instead to be the guaranteed harmless target point for a lightning strike.

Lightning dissipaters, such as the “Bottle Brush” Air Terminals, have been widely discredited and criticized by lightning researchers and professionals over the last 30 years.

Blunt or rounded Air Terminals have been shown to be slightly more effective than sharp Lightning Rods, because they have lower breakdown voltages, and longer time to breakdown compared, to other air terminals*

The basic principles of lightning protection are:

1) provide preferential strikes point for lightning
(an array of conductors higher than the objects being protected), a good grounding system, and conductors between the two to conduct the damaging current from a lightning discharge away from the boat.

2) provide appropriate transient protection on power and signal wires entering the boat to protect equipment and personnel from the effects of induced lightning currents.

An Air Terminal (Lightning Rod) is a passive device, which serves as a sacrificial device when the lightning strikes it, rather than the occupants, boat, mast, or antenna.
The other components of the standard Lightning Protection System are the down conductor and the earth terminal. The function of the down conductor is to channel the lightning current safely from the Lightning Rod to the ground terminal. The function of the ground terminal is to safely dissipate the large lightning current into the water (ground) effectively. Together, they form a low impedance grounding system, which dissipates the lightning strike energy, with a minimal rise in ground potential .

The results of studies suggest that moderately blunt metal rods (with tip height–to–tip radius of curvature ratios of about 680:1) are better lightning strike receptors than are sharper rods or very blunt ones.

Dr. Charles B. Moore et al, reported* that the electric fields above the blunter rods were as much as two times stronger over greater distances than those above the sharp rods. This, he said, ''can be significant in the possible interception of an approaching lightning streamer.''
Moreover, Dr. Moore said, “the sharp rods create around their tips a dense sheath of electrified, or ionized, particles, which reduce the probability of lightning's striking the rod. In so protecting itself from lightning, instead of drawing it, the rod is not as likely to fulfill its intended function of diverting lightning from other exposed objects in the vicinity. “

Goto: Lightning Rod Improvement Studies
By C. B. Moore, William Rison, James Mathis, and Graydon Aulich
Langmuir Laboratory for Atmospheric Research (New Mexico Tech)

Abstract:
AMS Online Journals - Lightning Rod Improvement Studies

Full Text (from Journal of Applied Meteorology, May 2000):
http://ams.allenpress.com/perlserv/?...t-document&doi

29-06-2008, 03:10	#11
GordMay Registered User Join Date: Mar 2003 Location: Thunder Bay, Ontario - 48-29N x 89-20W Boat: C.L.O.D. (Cruiser Living On Dirt) Posts: 12,577	Lightning Rods (Air Terminals) are placed on top of sailboat masts, not to dissipate any accumulated static charge, but instead to be the guaranteed harmless target point for a lightning strike. Lightning dissipaters, such as the “Bottle Brush” Air Terminals, have been widely discredited and criticized by lightning researchers and professionals over the last 30 years. Blunt or rounded Air Terminals have been shown to be slightly more effective than sharp Lightning Rods, because they have lower breakdown voltages, and longer time to breakdown compared, to other air terminals* The basic principles of lightning protection are: 1) provide preferential strikes point for lightning (an array of conductors higher than the objects being protected), a good grounding system, and conductors between the two to conduct the damaging current from a lightning discharge away from the boat. 2) provide appropriate transient protection on power and signal wires entering the boat to protect equipment and personnel from the effects of induced lightning currents. An Air Terminal (Lightning Rod) is a passive device, which serves as a sacrificial device when the lightning strikes it, rather than the occupants, boat, mast, or antenna. The other components of the standard Lightning Protection System are the down conductor and the earth terminal. The function of the down conductor is to channel the lightning current safely from the Lightning Rod to the ground terminal. The function of the ground terminal is to safely dissipate the large lightning current into the water (ground) effectively. Together, they form a low impedance grounding system, which dissipates the lightning strike energy, with a minimal rise in ground potential . The results of studies suggest that moderately blunt metal rods (with tip height–to–tip radius of curvature ratios of about 680:1) are better lightning strike receptors than are sharper rods or very blunt ones. Dr. Charles B. Moore et al, reported* that the electric fields above the blunter rods were as much as two times stronger over greater distances than those above the sharp rods. This, he said, ''can be significant in the possible interception of an approaching lightning streamer.'' Moreover, Dr. Moore said, “the sharp rods create around their tips a dense sheath of electrified, or ionized, particles, which reduce the probability of lightning's striking the rod. In so protecting itself from lightning, instead of drawing it, the rod is not as likely to fulfill its intended function of diverting lightning from other exposed objects in the vicinity. “ Goto: Lightning Rod Improvement Studies By C. B. Moore, William Rison, James Mathis, and Graydon Aulich Langmuir Laboratory for Atmospheric Research (New Mexico Tech) *Abstract:* AMS Online Journals - Lightning Rod Improvement Studies *Full Text* (from Journal of Applied Meteorology, May 2000): http://ams.allenpress.com/perlserv/?...t-document&doi __________________ Gord May ~~_/)_~~ (Gord & Maggie - "Southbound") "If you didn't have time/$ to do it right in the first place, when will you get the time/$ to fix it?"