Earthing a metal boat

[Piers]

A dear friend of ours is having a steel dutch barge built. The question that's attracting a great deal of debate is whether the hull should be earthed or not.

Anyone know the reason and logic behind earthing or not?

 

[[2068]]

From another post on this topic:

http://www.ybw.com/forums/showthrea...-earthing-in-a-steel-boat#zjMhTOlVxSl50kRl.99

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The earth must be connected to the hull at the same or as near as possible to where the 12v negative is connected.
This then gives you the problem of isolating the incoming earth when connected to a shore line this can be done with an iso transformer or a Galvanic isolator your choice.
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[MapisM]

Anyone know the reason and logic behind earthing or not?

I don't, but in a few steel boats I came across, the hulls were definitely earthed.
Btw, coming to think of it, if there would be any strong reasons AGAINST earthing, I wonder how safely/reliably (and for how long) the hull could be completely isolated, in real world...

 

[rogerthebodger]

A dear friend of ours is having a steel dutch barge built. The question that's attracting a great deal of debate is whether the hull should be earthed or not.

Anyone know the reason and logic behind earthing or not?

On my steel boat I have connected the mains earth to the steel hull at only one point through a galvanic isolator.

I also differ from those who say that the DC negative must also be connected to the steel hull at the same point.

My reasons are like any metal casing of a mains powered appliance the earth hull connection is to protect any one from getting a shock if a short ever occurs between the mains live and the hull i.e the case of an appliance.

In my vies the DC system negative must be isolated from the steel hull to prevent/reduce the possibility of of DC current loops in the conductive metal hull and possibility of excess anode erosion. I see no logical reason to connect any DC negative to hull of anodes as it just provides for a current path for galvanic corrosion.

On a metal hull the anodes must be connected to the hull to prevent galvanic corrosion.

It is now considered unnecessary/undesirable to connect all the anodes on a GRP boat together only connect the anodes to the item the anode is protection.

I have also eliminated as many different metals on my boat to again reduce the galvanic corrosion this causes.

My boat is in sea water if your boat is always in fresh water there is less risk as fresh water is not sa good as sea water as the electrolyte needed for galvanic corrosion.

 

[grumpy_o_g]

On my steel boat I have connected the mains earth to the steel hull at only one point through a galvanic isolator.I also differ from those who say that the DC negative must also be connected to the steel hull at the same point.My reasons are like any metal casing of a mains powered appliance the earth hull connection is to protect any one from getting a shock if a short ever occurs between the mains live and the hull i.e the case of an appliance.In my vies the DC system negative must be isolated from the steel hull to prevent/reduce the possibility of of DC current loops in the conductive metal hull and possibility of excess anode erosion. I see no logical reason to connect any DC negative to hull of anodes as it just provides for a current path for galvanic corrosion.On a metal hull the anodes must be connected to the hull to prevent galvanic corrosion.It is now considered unnecessary/undesirable to connect all the anodes on a GRP boat together only connect the anodes to the item the anode is protection.I have also eliminated as many different metals on my boat to again reduce the galvanic corrosion this causes.My boat is in sea water if your boat is always in fresh water there is less risk as fresh water is not sa good as sea water as the electrolyte needed for galvanic corrosion.

I'm glad you said that - I couldn't work out why connecting a steel hull to the negative side of the battery would ever be a good idea, especially one in saltwater.Reconsidering what I have written - are we talking about connecting the battery negative to the hull, the shore power earth to the hull or actually earthing the hull (i.e. ensuring that there an electrical path between the hull and the water/mud in which the boat is)?

 

[VicS]

A dear friend of ours is having a steel dutch barge built. The question that's attracting a great deal of debate is whether the hull should be earthed or not.

Anyone know the reason and logic behind earthing or not?

The wiring should should be in accordance with the latest editions of ISO 13297 and ISO 10133

ISO 13297:2014 specifies the requirements for the design, construction and installation of low-voltage alternating current electrical systems which operate at nominal voltages of less than 250 V single phase on small craft of hull length up to 24 m.

SO 10133:2017 establishes the requirements for the design, construction and installation of extra-low-voltage direct current (d.c.) electrical systems which operate at nominal potentials of 50 V d.c. or less on small craft of hull length up to 24 m.

Anyone wiring a boat should be familiar with these two standards. A professional will follow their requirements


There should be a single earth connection to a steel hull above any anticipated bilge water

 

[rogerthebodger]

I'm glad you said that - I couldn't work out why connecting a steel hull to the negative side of the battery would ever be a good idea, especially one in saltwater.Reconsidering what I have written - are we talking about connecting the battery negative to the hull, the shore power earth to the hull or actually earthing the hull (i.e. ensuring that there an electrical path between the hull and the water/mud in which the boat is)?

The mains earth connected to the hull.

The hull will be electrically connected to the water in my case through at least the anodes that are connected to the steel of the hull through studs welded or the anodes welded directly to the hull

My propshaft is totally insulated from the hull but has its own anodes as does my steel rudder.

The DC negative not (this is ans isolated DC system.

VicS knows the ISO standards better than I, but in one of then an isolated DC system was allowed if I remember correct

 

[Piers]

So.....

Assume 1) that the steel hulled boat has shore power but uses an isolation transformer so there's no earth coming from shore power. Then 2) assume everything electrical is isolated from the steel hull.

Why bond to the hull?

If it's in case of something live touching the hull, use a galvanic isolator between the hull and the supply, immediately to trip all the CBs.

What's wrong with this?

 

[rogerthebodger]

So.....

Assume 1) that the steel hulled boat has shore power but uses an isolation transformer so there's no earth coming from shore power. Then 2) assume everything electrical is isolated from the steel hull.

Why bond to the hull?

If it's in case of something live touching the hull, use a galvanic isolator between the hull and the supply, immediately to trip all the CBs.

What's wrong with this?

In this case connect one side or the output of the isolation transformer to the hull this becomes the neutral. Then connect a RCD in the supply and the neutral (connected to the hull) between the appliances you are powering and the isolation transformer. the incoming earth will be connected to the case of the isolation transformer.

No DC connections to hull

 

[PCUK]

My 30 year old steel hull has DC earthed to hull as is correctly recommended. No AC isolator for shore power and no problems

 

[Piers]

This has become really interesting and has led me to think about Electric Shock Drowning. I'll start a new thead for this so it's seen as a fresh subject.