Since you are only asking about the second half of lightning vs. vessels - the answer is rather simple. You want to provide the easiest low resistance path for a lightning strike to pass through the boat to ground/ocean.
- - To do this you need the equivalent of 4 sq ft of copper plate -minimum- mounted in the water. To this plate you attach a welding cable of at least 2/0 to your main mast with virtually no bends in the cable between the attachment to the plates and the attachment on the mast. The best attachment device for an aluminum
mast is a pre-made bimetallic grounding lug which is available but difficult to find. It is a casting made with one half being aluminum
and the other half bronze.
- - Lightning will connect with the highest thing near or on your vessel which with a sailboat is normally the main mast. Aluminum conducts electricity better than stainless steel
so the energy will try to flow down the mast first. If you have a nice "fat" escape route
via the welding cable and grounding plates the energy will complete its journey with probably minimal damage to your vessel.
- - However, if there is no "escape path" for the energy it will then (all of this occurs in nanoseconds) try going down the stainless steel
shrouds where it will encounter that super skinny bonding wire system connecting everything metal together. In this case now your vessel is the inside portion of a surging electromagnetic field which will happily fry most of your electronics
. And still trying to get through your boat to earth/water ground it can and has passed through your bronze through-hulls raising their temperature sufficient enough to melt the FRG and allow the through-hulls to fall out of the boat. Now you have 1.5 inch open holes allowing sea water to enter the boat. Although not in ABYC yet, bonding bronze through-hulls is generally not considered a good idea.On the other hand not bonding bronze through-hulls to a zinc can lead to tin leaching out and through-hull failure. (pick your poison).
- - The sintered bronze grounding plates (Dyna-plates, etc.) are, if you read the label carefully, listed as "equivalent" to "x" square feet of copper. Which they are when newly installed. But before long all those nooks and crannies fill up with sea life and there goes your "equivalent" sq. ft.
- - Wooden masts generally have a thick copper strap that runs down the length of the mast of give the energy of a lightning strike an easy path to ground versus splintering the wood.
- - However, all of the above is theoretical and looks good on paper and has "theoretically" worked on some vessel struck by lightning - it is not a guarantee or "sure-thing." Mother Nature does what Mother Nature wants to do and she does not read our physics books
- - And secondly installing a proper grounding path system for a lightning strike is both expensive and time consuming and when you consider the probability of being hit is very, very low some folks and manufacturers all consider it not cost-effective. There are a lot of more probable high risk things that can sink a boat which will consume most of your money
trying to prevent.