Is the signal digital (on/off) or an analog voltage?
Okay looks digital.
Where comes the 2A from? You can measure a voltage or a current, but not both with a single input.
I'd dimension the signal voltage divider for 1mA, in order to make it somewhat insensitive to noise. Also add some safety precautions, because the 12V on a boat can mean anything from about 9V to 16V, with spikes of 100V and more. An opto coupler is fine for digital inputs.