You can install a grounding plate near your centerboard well and run the engine ground to that. Now it doesn''t matter if the engine is up or down
2. Install another ground plate straight below the mast(electricity doesn''t like to turn corners). Now run your no. 4(at LEAST no. 4) to that. I think the best way to avoid a lighting strike is to avoid a lighting strike. This can be done by not allowing the static electricity to build up. Lightning just doesn''t strike, it is "provoked" by static electricity building up in your rigging and then jets skyword in the form of a streemer luring the strike. A electrical engineer told me the best thing to do to avoid this is to cable clamp a no. 6 tinned wire to the upper shroud base on each side of the boat,strip 6" of insulation off the other ends, solder up those ends and simply drop them into the water. (I''ve done this on my boat).This gives the static electricity a chance to bleed-off thus preventing a streemer thus preventing a strike. But remember, there are no absolute guaranties against a lightning strike.