Hey Mate, sorry this is my first time wiring so sorry I'm a little confused.
The wiring in my boat is really all over the place making it a little difficult. I have one battery for my boat that is for cranking + all electronics. This is situated to the back of the boat, and it has a positive and negative wire running up into the console. These wires are quite a heavy gauge and the positive and negative wires are separately connected to a little device similar to a busbar but they only have one tiedown/nut down (I'll call them a tiedown/nut down busbar) spot for the wires. So all my electronics, nav lights etc have their postive wire connected to the single tiedown/nut down positive busbar and their negative wire connected to the single tiedown/nut down positive busbar, with the thick wires also connecting to these, running back to the battery. There is also a 6 switch fuse switchpanel which some devices are connected too. So my sounder has its negative and positive wires which I will just connect to the postive/negative tiedown/nut down busbar's and also another wire which I will connect to the switchpanel. But the sounder also has a specific wire coming from a separate port at the back of it that needs to be grounded. However since this is a small fibreglass boat I dont think I have a ground, thus I'm wondering how it should be done.
Sorry for the long post, but any help would be appreciated.
Cheers.