Fusion Stereos - A word of Warning

[Noelm]

A couple of things need to be investigated here, if you have a fiberglass boat, then how does it get the earth return? The screws you mention may indeed be earthed, but I am pretty sure the power cable has a black and a red wire? I if hats not he case, hen insulating it from the Aluminium boat, it will not work will it? Now to the GME radio, I have a main battery switch, and my radio keeps the stations as they were, even if the battery switch has been off for a week?

[scottar]

It is just that the case provides another connection to earth - same as every car stereo ever made pretty much. The case is not used as a negative to actually run the unit but is grounded in an attempt to minimise electrical noise. It generally isn't a point of contention with an outboard powered tinny as the hull is grounded (connected to negative) via the outboard anyway but could well be an issue with a larger alloy rig that is inboard powered with no negative connection to the hull.

One of the biggest safety issues in this situation is that the radio may become a path for a short circuit if the positive from the battery or any heavy current positive makes contact with the hull. If there is no fuse in the negative line, the much lighter negative wire on the stereo unit would very probably melt or catch fire.

This is not typically going to be what would happen in an outboard powered rig as the much heavier negative via the outboard should carry most of the current. That said - if there is no fuse in the negative stereo line and the unit is mounted directly into an alloy dash, it would not hurt to fit one just to be on the safe side.

[Noelm]

That's more or less what I was alluding to, being earthed does not mean it is supplying the return to run the device.

[Fed]

I think that's exactly what it means noel, whenever the radio is on or the motor is running there would be current flow through the hull.

Bad case would be a dodgy negative connection to the motor either at the block or at the battery then the hull & the radio negative could start carrying higher currents and you may not even know about it.
Galvanic corrosion pales into insignificance when compared to electrolysis.
I say there should only ever be one negative to a tinny hull and that's via the main engine negative and the motor bolts.
You could go nuts thinking about this stuff, too may wotifs for me.