Ships earthed or not?

[jenevers]

Someone once told me that Ships are not earthed electrically. Is this true or not?

[Scholar Gypsy]

See other recent thread on galvanic transformers. The neutral and earth on electrics within a ship/boat should be bonded to the hull.

 

If the ship is moored then you need to be careful if you connect that earth to the landside earth connection.

[bizzard]

Not to mention Degaussing circuits of cable for the likelihood of getting blown up by magnetic mines, no singular, 'mine' as you're only likely to be blown up once.

Edited May 3, 2015 by bizzard

[raymondh]

Most large ships use an insulated neutral distribution system which I think has no connection to "earth"

 

Ray

[Timleech]

Someone once told me that Ships are not earthed electrically. Is this true or not?

 

Certainly some are not, I believe that used to be the norm. Fashions may change, of course, even with electrics, I've no idea what they do with modern ships.

 

Tim

[bizzard]

I don't know, but if earthed to the actual earth of mother earth and not via the water, the ship would have to be kept earthed to it by a massively long cable connected to say a metal lamp-post on the promenade and pay out and haul in miles and miles and miles of cable wherever it went.

[Timleech]

I don't know, but if earthed to the actual earth of mother earth and not via the water, the ship would have to be kept earthed to it by a massively long cable connected to say a metal lamp-post on the promenade and pay out and haul in miles and miles and miles of cable wherever it went.

 

http://www.bbc.co.uk/staticarchive/5d3a5690c0c3a16ea35477564bf2638fc432655f.jpg

[bizzard]

 

http://www.bbc.co.uk/staticarchive/5d3a5690c0c3a16ea35477564bf2638fc432655f.jpg

Bet they've got a headache. That's the trouble being amongst lots of electrical fields with all those electrons buzzing about. I know folk whose boats are 'power station boats' and they often complain of continual nagging headaches to the point where taking loads of pills have no effect. They gain a little relief now and then when they turn it all off. Perhaps if they wrapped themselves round and round with wire to degauss themselves it would repel the bombardment. A big opposite pole repelling magnet bolted to the scalp might help and save them from a horrible and dizzy fate.

[Mac of Cygnet]

I put this question to Son No 2 who is an electrical engineer on a seagoing ship. Here is his reply (not that I understand it!)

 

 

 

Opening post is right and wrong... Most ships electrical systems do not have a neutral and therefore earthing in way people think of it does not happen. Equipment is still bonded to the ship's hull so that in the event of a fault, the voltage potential is tied to the hull rather than just the local electrical equipment. This means that the hull is essentially 'floating' and can be at anything between zero and several hundred volts potential to the supply. It is set up like this to prevent a single 'earth' fault (short circuit between line and hull) on any one phase causing failure of equipment. If two 'earth' faults occur, on separate phases, a direct short circuit results in instantaneous tripping of the motor, breaker, etc. With high voltage systems (anything over 1000V on a ship, again, different from shoreside which I believe is tens of thousands of volts), the neutral is connected to the hull of the ship, though not directly. High voltage is is totally different kettle of fish however and I suspect it's not really of interest here.

[ditchcrawler]

Someone once told me that Ships are not earthed electrically. Is this true or not?

If you are talking real ships then some of them have some earth free systems and normally have earth fault monitoring. There are times when an earth fault blowing a fuse could be more than embarrassing.

[Timleech]

It used to be the norm for boats, even narrow boats, to have their electrics isolated from the hull. Some still are, including mine

Basically, that changed when vehicle-type engines became the norm, and it would have been expensive to isolate their electrics.

Now that the change has been made, the 'experts' tell us we're better off with the neutral bonded to the hull.

 

 

 

Tim

[Arnot]

It was indeed the norm. But, things have changed since then, RCD's have become more reliable and a whole lot cheaper. And - we have a generation of boaters who expect to be able to plug a toaster in, and why not?

 

The concept of earthing the hull is to ensure that an RCD operates at the earliest possible moment, ideally before the fault voltage or current becomes high enough to initiate combustion or death. If the hull were to be insulated from the mains electrical system, then if a short circuit between the "live" conductor and the hull would not necessarily trip the RCD and prevent the hull from becoming live.

 

Of course, at sea this is a redundant concept but when moored and connected to shore power, if someone were to board or disembark a faulty boat and accidentally touch both the hull and any shore connected metallic device at the same time, they would get a sharp belt.

 

In the case of bigger ships, they can generate sufficient power to be self sufficient and so rarely if ever connect to shore power. But - in the case of smaller craft, pleasure craft and particularly narrow boats, a connection to shore power is commonplace.

 

The risks are somewhat mitigated by using a correctly configured isolation transformer but even then, the extra safety provided by bonding the neutral to the hull as an earth point is significant, whereas the cost of the bit of wire, a terminal and a bolt is not.

 

The real downside of course is that if the mains supply to the boat is problematic and no isolation transformer is used, it can lead to hull erosion and pitting.

 

Oh and BTW, I'm no "expert", I'm old enough to remember Blaster Bates...

 

Hi Tim!

 

Regards

 

Arnot

[Timleech]

It was indeed the norm. But, things have changed since then, RCD's have become more reliable and a whole lot cheaper. And - we have a generation of boaters who expect to be able to plug a toaster in, and why not?

 

The concept of earthing the hull is to ensure that an RCD operates at the earliest possible moment, ideally before the fault voltage or current becomes high enough to initiate combustion or death. If the hull were to be insulated from the mains electrical system, then if a short circuit between the "live" conductor and the hull would not necessarily trip the RCD and prevent the hull from becoming live.

 

Of course, at sea this is a redundant concept but when moored and connected to shore power, if someone were to board or disembark a faulty boat and accidentally touch both the hull and any shore connected metallic device at the same time, they would get a sharp belt.

 

In the case of bigger ships, they can generate sufficient power to be self sufficient and so rarely if ever connect to shore power. But - in the case of smaller craft, pleasure craft and particularly narrow boats, a connection to shore power is commonplace.

 

The risks are somewhat mitigated by using a correctly configured isolation transformer but even then, the extra safety provided by bonding the neutral to the hull as an earth point is significant, whereas the cost of the bit of wire, a terminal and a bolt is not.

 

The real downside of course is that if the mains supply to the boat is problematic and no isolation transformer is used, it can lead to hull erosion and pitting.

 

Oh and BTW, I'm no "expert", I'm old enough to remember Blaster Bates...

 

Hi Tim!

 

Regards

 

Arnot

 

Hi, good to see you back.

Actually my last post was meant to refer to DC on small boats, slipped up by mentioning 'neutral' instead of Negative!

My boat has 24V DC isolated from the hull, but the 240V wiring (shore power and inverter) is indeed bonded to the hull, with RCDs, in the modern manner.

 

Tim

[jenevers]

As a matter of interest is there any record of anyone ever being killed due to a hull not being earthed.

[ditchcrawler]

As a matter of interest is there any record of anyone ever being killed due to a hull not being earthed.

Gibbo said there was but he was not quoting the UK at the time.

[MtB]

Someone once told me that Ships are not earthed electrically. Is this true or not?

 

 

The point made amusingly by Mr Bizz earlier is that your question is rather fuzzy. Have a think about what you mean by "earthed electrically", precisely.

 

Then I think (hope!) you might decide to re-frame your question.

[by'eck]

As a matter of interest is there any record of anyone ever being killed due to a hull not being earthed.

 

Link

[jenevers]

The point made amusingly by Mr Bizz earlier is that your question is rather fuzzy. Have a think about what you mean by "earthed electrically", precisely.

 

Then I think (hope!) you might decide to re-frame your question.

OK. Do ships have their neutral connected to earth and their hulls?

[ditchcrawler]

OK. Do ships have their neutral connected to earth and their hulls?

Some ships do and some ships don't, on some circuits it is and some it isn't.

Not very helpful but a fact

[MtB]

OK. Do ships have their neutral connected to earth and their hulls?

 

I'll be more specific then! The 'earth' is a big stake driven into the ground, broadly speaking. A mobile ship by definition cannot have one of these.

 

How do you expect a ship to connect it's neutral to earth?

[jenevers]

I'll be more specific then! The 'earth' is a big stake driven into the ground, broadly speaking. A mobile ship by definition cannot have one of these.

 

How do you expect a ship to connect it's neutral to earth?

So boats don't need an earth cable? Just live & neutral.

[by'eck]

So boats don't need an earth cable? Just live & neutral.

 

When ashore you stand on earth. On a boat its the hull electrically speaking. If you substituted hull or even boat ground for earth I'm sure it would satisfy the pedants, although I suspect they already know what you mean.

[bizzard]

To be safe I can only suggest that when going anywhere by ship or in your boat with an inverter switched on to insulate yourself by binding yourself up entirely from head to foot with miles of insulating tape and to wear over that a rubber wet suit, gloves and boots and don't touch anything. To make doubly sure of not getting any shocks on your boat or while the ship is at sea, drag, by hand a cannonball along the seabed on a chain or wire cable to earth yourself, which you should not under any circumstances let go of, for fear of sharks, no shocks.

Edited May 9, 2015 by bizzard

[jenevers]

When ashore you stand on earth. On a boat its the hull electrically speaking. If you substituted hull or even boat ground for earth I'm sure it would satisfy the pedants, although I suspect they already know what you mean.

Me too.

[Arthur Brown]

Ships use many earthing regimes. Some have hull referenced neutral, some run a power supply unconnected to the hull. Some use USA voltages (120) Some a more typical European voltage (235 ish) Some container ships supply huge amounts of three phase to refrigerated containers.

 

New ships intended to sit cold iron when it port will have an 11KV substation on board and power the moored vessel from shore supply, which is better from the point of engine emissions. -Their shoreline is a bit special and has multiple sense pins to ensure that it's dead at both ends but connected at both ends before the 11KV switch on happens.

 

Technically the hull of a boat is always grounded because "ground" includes all the water mass of the oceans, so only a plastic boat with no metal fittings could isolate inside from outside. (and if you are in a canoe than you are wet anyway)!