24 volt wiring question

currently, on my bass boat i have 2-12 volt batteries.
one is for my gas outboard starting.
the second 12 volt is for my trolling motor, depth finder livewell pump.
iam going to replace my existing 12 volt trolling motor with a 24 volt system, using an extra 12 volt battery wired to produce 24 volts.
can i isolate 12 volts from that 24 volt setup to power my 12 volt accessories ?
my thought is that i have to re-route my 12 volts to my extra 12 volt battery i use for my gas engine.
i hope that makes sense

you'd be better off keeping all the 12v stuff on one battery.....you can do what you described, but one battery will run down before the other and the trolling motor will know it.

best solution would be four batteries - one for the engine, two for the trolling motor and the last for the accessories - but it comes with the weight penalty.

Makomark's solution is the best and most straightforward. The 24 V trolling motors are sensitive to unbalanced battery power. Typically you will be using your fish finder and MAP/GPS while using the trolling motor with the main charging motor off, so you don't want to be using your cranking battery to power accessories.

However, I've seen diagrams of a 3-battery setup that allows the accessory load to some off of the 24-volt set-up using some sort of electronic box that keeps everything balanced. Don't remember what it is called or how well it works. An internet search of "24 volt marine wiring" or something like that will likely lead you there.