Earthing batteries on steel boats

[Baggywrinkles1]

My engine starting batteries are earthed to the hull (steel) The surveyor says they should be earthed to the engine. Will this not just transfer any electrolosis to the engine though? Some engines have anodes but mine does not!! Comments please.

 

[noelex]

Each earth point is at a slightly different voltage and this creates the potential for corrosion when immersed in seawater.
Metal boats use a couple of solutions to overcome this problem.
1. Earth the boat above ground, so no earth wires are in contact with the hull ( this is the best system)
2. Create a single earth point.

If the engine and hull are earthed you are not creating a single earth point, but many metal boats create an earth point on the hull and isolate the engines earth.

Is the engine isolated ?
Clues that it is isolated will be each sender will have 2 wires attached to it and there will be a large negative relay near the engine.

 

[vyv_cox]

The need for engine anodes is dependent upon whether it is raw water or indirectly cooled. Indirectly needs no anodes, same as your car, and corrosion will be kept under control by using antifreeze with inhibitor. The heat exchanger may need one though, dependent upon the materials of construction. Raw water cooled engines need an anode but the location of the earth is not critical.

 

[VicS]

My engine starting batteries are earthed to the hull (steel) The surveyor says they should be earthed to the engine. Will this not just transfer any electrolosis to the engine though? Some engines have anodes but mine does not!! Comments please.

There should be a direct connection between the engine and the battery negative

The DC negative may also be connected to the hull except when a fully isolated system is used.

The steel hull should not be used for current carrying in the way that a car body is. The negative wiring of all equipment should be independent of the hull.

The earth of a shore power installation should be bonded to a steel hull and a galvanic isolator fitted, unless an isolation transformer is used

Some engines have anodes some do not.
Indirectly cooled engines do not need anodes themselves as they are protected from corrosion by the inhibitors in the antifreeze/summer coolant. There may or may not be an anode in the raw water side of the heat exchanger it depends upon the materials used .
Older directly cooled engines may not have an anode. More modern ones are likely to have an anode.

 

[Baggywrinkles1]

Earthing Batteries on steel Boats

Thanks advice. I would mention I have a barge in fresh water with keel cooling is it better to earth through the engine or the hull? There are no engine anodes. Daf 575.

 

[noelex]

The most important thing is to have a single earth. The hull is generally the preferred option, but the engine should be ideally isolated.
If the boat will stay fresh water the concerns will be less, but I have little practical experience with metal boats in fresh water.