LIGHTNING GROUND PLATES:
A good Ground requires a direct and permanent immersion in seawater. It must also have sufficient area, mass, and edging to adequately dissipate the strike energy. Electrical
energy dissipates better through edges and points, that it does through flat surfaces.
Minimum design criteria for this ground plate by ABYC-E4 standards are:
• Minimum area – one square foot totally submerged for salt water
(more for fresh water)
• A Ground Strip is preferred to a rectangular plate.*
• Thickness – minimum of 3/16"
• Width – minimum of 3/4" (for a grounding strip)
• Materials – copper, copper alloy, stainless steel
or aluminum. (others have suggested adding monel or navel bronze)
Other important guidelines relative to designing the external ground plate are:
(1) the ground plate should be located as close to directly under the down conductor (mast) as possible;
(2) the edges must be sharp and exposed, and not caulked or faired into the adjoining hull surface;
(3) *the grounding strip, if used, should extend from directly below the mast
towards the stern and be electrically connected to the aft end of the engine
(a minimum strip length of 48" is recommended, with an appropriate width to yield at least 1 sq. ft of area); and
(4) a pair of thru-bolts should be installed at each end of the strip to prevent it from twisting. Intermediate bolts may be used as necessary.
Ewen Thomson, Ph.D (Marine Lightning
Protection Inc): http://www.marinelightning.com/
“Lightning& Sailboats” Florida Sea Grant
“A Critical Assessment of the U.S. Code for Lightning
Protection of Boats”
IEEE - Transactions on Electromagnetic Compatibility
“Comments on ProBoat Article”
In the December/January 2003/2004 issue of Professional Boatbuilder , pages 26 - 43, Nigel Calder gives a comprehensive analysis of lightning protection. While Calder's article was particularly well written and accurate, we felt that some of his scientific comments could benefit from some elaboration. Specifically, the role of ground plate edges has suffered from a drift in interpretation over time. Consequently, we submitted a letter that was subsequently published in the 2004 April/May issue, pages 4 - 6. The exchange concerning lightning dissipaters on pages 6 - 10 is also well worth reading.
Lightning Grounding Systems - Basic Theory & Practice ~ by Johnathan Klopman
ABYC ~ “LIGHTNING PROTECTION” - Standard E-4