Shore power and solar power

No, nothing catastrophic will happen and you don't have to disconnect the solar system when you turn on the shore power charger.

The job of the solar charge controller is to monitor the state of the batteries and control the amount of solar power going to them.  If something else charges the batteries too, the solar controller will throttle back its charge accordingly.

I have a similar setup, except I'm in an office and not on a boat.  My Renogy 100W kit charges two deep cycle batteries, but I also have a Schumacher battery charger hooked to the batteries at the same time.  If I have an extended period of cloudiness and want to supplement with the battery charger, I just turn it on and let it do its thing.  If, while I'm doing this, the sun comes out, the Renogy controller will add any appropriate available current to the mix.  When the batteries reach full charge, both systems scale back their levels to a shared float charge.

Been running this system for quite some time now with no catastrophic events...so I think you'll be just fine.

paulh,

I'm totally with you on that! To me, there is no such thing as "too many fuses" or "too high a margin for safety."  Not after what I've seen in my years of working with electronics.

When someone sees my solar setup and asks, "why in the world do you have a fuse there?" or comments, "that's overkill...it could never get that hot" or similar things, I ask them "Have you ever personally experienced a flooded deep cycle battery explosion?"

I have.  Fortunately, it was at a Fire Department Academy demonstration/training event and we were well clear of ground zero.  But it was impressive.  Think giant grenade sending bits of superheated acid and shrapnel flying in all directions at high speed!

No way I'm taking any shortcuts with two of those things anywhere near me.