Here is my understandings from speaking with and correspondence with Dr. Thomson.
The edge effect of a conducting plate underwater is mainly at the points of the corners, so it is as effective or more effective, to have one point and a bigger one at that, hence the through
hull conductor. The principle is to give the
electrical voltage field the easiest path to ground, as we've all heard. I believe the evidence is partially based on voltage discharge experiments with high speed
photography. I am not sure of the
references for this.
As Hellosailor has outlined, the same high speed photography/film also shows lightning discharges at the surface film where the charges balance, in milliseconds. The Siedarcs are therefore placed as close to the waterline as possible.
It's a bit easier to locate the bridgedeck conductor as it is adjustable, so we will lower it to the sea surface when at
anchor, in case a thunderstorm comes during the night.
The specs of how to implement the system are part of Dr. Thomsons
service so it has the highest effectiveness.
As far as effectiveness, I spoke to a cruiser in
North Carolina who was struck, he believes, on his cat while at
anchor in
Florida with no damage to any
equipment, but it's my only user data point. Still, since cats are struck about twice as often as monos and suffer on average much more damage, (US
Boating Association study) I think it's as good a preventative measure as there is, so we're going with it during our build. Its easier to run the
cables when there is good access rather than after all furniture and interiors have been installed.
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