I'll stay out of it for now, however you are
mistaken Cred about "almost guaranteeing" engine electrics are grounded,
indeed most proper marine engine electrics are not.


How can they not be? Every DC and AC motor I know of requires a + and -
current to run. I consider the - to be ground. The outdrive is connected to the
engine which must have a + and - (or ground) to run, and is fastened to the
metal hull. If theres no continuity there you will have to show me with a VOM.

True marine electrics even on big diesels where the spark risk is
minimal, have all their electrics above ground.

Define "above ground". Again, they require a positive and negitive to operate.


The starters &
alternators etc have their own earth returns kept above the cases, so if
the user/engine manufacturer chooses you can have a completely above
ground system with none of the electrics able to get to the prop shaft
etc via the block.

And the block is grounded (or negitive) and is connected metal to metal to the
metal outdrive which is bolted to the metal hull. The connection might not be
the best but it is there and I have to believe its making a pretty decent
connection. I have an aluminum boat with an outboard and there is definately
continuity from the hull to the motor.. It would take some pretty serious
custom made isolators to stop it.
I can admit it when I'm wrong so if someone can show me that I am I would like
to know how they work.