avb, "practical" is a personal and objective call.
EMP from a lightning
strike is a lesser concern than being in the path itself. Ham radio
operators often follow the path of using a 'bulkhead' connector in the wall or window of their home, and all wires that come in from the outside (i.e. antenna
cables) can be unplugged at the bulkhead and then moved to an external ground connection, so any strike travels through the cable and then down to ground--not inside to the equipment
. You could certainly do the same thing at the mast
, fit every cable with a disconnect and make up a second set of connections that take them directly to the lightning ground at the mast
. (Presumably to the keel
it is stepped on or over.)
Disconnecting at the rear of the instruments isn't quite as effective as that still leaves wires to conduct power around inside the boat, and lighting
has been known to jump any way it pleases from one to another.
You could also install lighting
protection (i.e. from Polyphaser) at the mast, which would take at least some strikes. They have white papers on the topic and are a leading supplier to folks who cannot afford to disconect during storms, like broadcast stations.
As to a Faraday cage...IF your instruments were all in one location, you could certainly fabricate a rear shield for the location, and a removable front cover. Bulkhead the cables
with one disconnect block of some type, secure the front cover (with conductive fingers all around it) whenever you weren't using the insturments, and how practical that is, is up to you.
Stowing the handhelds (GPS, VHF
, etc.) in a metal oven
or microwave cabinet, or large metal cookie tin, is probably more practical but of course, won't protect the hardwired stuff.