Roger Long wrote:

It's a lot of work to produce a schematic that way. Scanners and digital
cameras are so common now that posting a jpg of hand sketch would be much
easier and clearer but newsgroup rules prohibit posting of images. If you
have a web site or friend with one, you could upload the image to the server
and post the link here as I do often.

You need better, or clearer, advice than you'll get here though. Try and
find a mechanic who knows boat systems.

I would recommend a dual output battery charger. It will make everything
much simpler.

In that scenario where does the alternator go?

Stephen