DC ground on Steelboat

[Lu_Be]

Hi all.


I'm about to completely rewire our new to us steel boat.

I'll have 2 Batteries, 1 Starter AGM and 1 LiFePo4 Housebank.

DC/DC Charger and a 230V charger. There is no inverter and no 230V system on the boat. Only 1 Landline to the Charger.



I came across different options of grounding...

I'll not try to completely isolate the systems, nor use the steel hull as a common ground.



The most logical way to me is to connect both negative of the batteries and then run a big grounding wire to a zinc anode.

Is this the right way to go?

[tkeithlu]

Bond everything together, but do not use the hull as a negative (or any other) conductor. Always run a negative wire as well as a positive wire to the use.

[Lu_Be]

Yes I will run a negative back to the bus-bar from every component.
The question is, do I connect the grounds of the battery to a anode at the outside?

Because the engine for example is a negative ground and has watercontact via the propshaft.

[noelex 77]

When wiring the DC system the first option of isolating the battery negative supply is the best solution for reducing the possibility of stray current corrosion, but this is also considerably more expensive to implement correctly. It requires dual switches and circuit breakers.

The simpler and cheaper option is to have one and only one DC negative connection to the hull. The risk of stray current problems is considerably higher and unfortunately it is difficult to monitor faults, but it is an acceptable solution.

Using the steel hull as a negative return is the cheapest option, but is not generally considered an acceptable practice.

The above is only an outline. If you want to include an AC system, especially shore AC power, things become more complex.

[Bowdrie]

Investigate "Impressed Cathodic Protection".
Best solution for a steel boat.

[Statistical]

Originally Posted by Lu_Be

Yes I will run a negative back to the bus-bar from every component.
The question is, do I connect the grounds of the battery to a anode at the outside?

Because the engine for example is a negative ground and has watercontact via the propshaft.

I would not add an extra connection to the water. You already have one via the propshaft and I assume the prop is protected by an anode.

Technically you don't even need that. It is possible to use a composite coupler to ensure the propshaft is isolated from the engine. It does require having an isolated alternator (many already are) and an isolated starter (very rare for this to be stock but it can be upgraded).

Avoiding all connections to the water is challenging so a compromise is a one planned connection to the water via the engine/propshaft and then provide an anode there. You have that. There is no reason to add another one.

[tkeithlu]

Own a reference electrode. They are easy to use - drop the electrode into the water, connect it to one pole on your multimeter, connect the other pole to the hull of your steel boat. You should get approximately 1 volt. Less, and you do not have enough aluminum plate anodes. I pull the boat and switch out the anodes when it drops to 0.8 volts. We own two sets, and wire brush them between uses. There are 14 plates plus a prop shaft doughnut on our 44' steel trawler. The two sets are still in use after 13 years. Here's a source:

https://www.boatzincs.com/corrosion-...ode-specs.html

[MicHughV]

I owned a homebuilt steel boat for a number of years. all my 12v dc runs had both pos and neg runs.
The engine sat on rubber mounted supports, and the shaft was led thru' a std. rubber stuffing box, so no direct electrical connection there.
I had a sacrificial zinc mounted to the hull....it was 12"x"6x 1". It lasted for years and years with minimal loss of material. My shaft zinc was also goof for about a year at a time.
The entire boat was painted with a zinc primer.
I can't say that I ever remember having a problem with electrosis of any kind.

I certainly would not recommend using the hull as a ground as that would seem to be an invitation to trouble.

The other plus with having a pos and neg run to any device is that it makes it easier to find a fault should one occur. Naturalyl each independent item was protected by it's own fuse or breaker at the panel.