Grounding 12v system

[neilmac]

Hi Guys

Is it necessary to earth a 12v systems to the boat. I'm replacing and the old wiring (and relocating the panel) and I notice that their is a green wire that appears to be attached to the bottom (below deck) of the Shroud chainplate. I have installed a Negative busbar. My research suggests that it may not be an issue for simple DC systems.

thanks Neil

[Greg]

Was there a 240v generator used on the boat at some point? The point of grounding is to give high voltages/amps a route to go other than through you. Can't see any point to doing this on a 12v system but I could be wrong?

[neilmac]

Hi Greg
Don't know about the 240v generator and I certainly won't be using one. The old wiring is a bit of a mess. I think i'll skip the earth.

[Ozzie]

Do you know if the boat was ever moored and if so was there a sacrificial anode on the boat. I have long forgotten the theory but that may have has something to do with it.

My old cruiser had sacrificial anodes as the tip of the OB dipped in and out of the drink on the mooring. I have nothing on Spritzig II as no metal is in the water except the swing keel.

Nothing had decayed after 10 years ......except me.

[neilmac]

I have found out that it was the radio (car style) that was earthed for some reason. Anyway I've taken out the radio.

[Steve]

Alot of radio/electronic equipment recommends RF grounding. I have the same wires that you have on the chain plates etc (another boat) that go to a - terminal for RF grounding the HF and Vhf

Steve

[atles]

just take it out i did all my wiring and 12 v just needs the bar
have fun with it

[Peter T]

The reason for using the negative side of the battery to earth is that if there is any electrolysis , then the chassis of any electrical equipment will be eaten away instead of the fine wiring of the electronic devices ( radio's etc). This is also why you use a sacrificial anode. Because of the direction that electrical current flows, the negative side is the sacrificial side, ie earth, chassis, anode. Also, if your aluminium mast etc is also connected to the anode, it gives a path for lightning to exit the boat via the anode. I knew of a chap who had it connected the wrong way and when lightning struck his mast, it found its way via all the electrical devices on his boat and ended up disapating itself through the depth sounder blowing a large hole through the hull at this point ending in the sinking of his boat. ALWAYS but ALWAYS fit an anode and have it connected to the negative side of the battery. Also it's a very good idea if the boat is moored, to electrically connect your mast to a chain hanging over the side of the boat into the water giving an easiest electrical path ( of lowest resistance ) to the water (earth) without going via the internal electrics of the boat.

Regards Peter T

[Ozzie]

Peter, David, I do have a small battery on board but I totally disconnect it when not on board as I have always done . I have on occasion connected a small solar panel (front window size) but it’s always just to the battery which is disconnected from the boat. I’ve never had any issues with electrolysis (so far ) and my cb as I’ve mentioned is still viable after 16 mooring years, which is where I figured issues might happen.

There is a fair bit of stuff on the net on having you vessel set up as a faraday cage for lightning strikes . As I have basically no electronics left in board I have not been too concerned. I think the chain over the side is probably a good idea and if caught out in a lightening storm I’d do that, with my anchor chain although I’ve read some reports that it’s ineffective. Best to avoid storms and not test these things

[Peter T]

Hi Ozzie, with what you are doing with your battery, you shouldn't have any problems although electrolysis can occur in a salt water environment between dissimilar metals, especially if you are for instance moored in a pen of a marina in close proximity to other boats. Stray voltages are a very strange thing. I won't be mooring my boat, so will not worry about an anode. When you consider that anodes are zinc blocks, it makes sense that because galvanised coating is Zinc, that the coating on the centreboard can get eaten away with any electrolysis.
Cheers
Peter T