Live metal work when out of the water?

[Piers]

Just be told by a Fairline owner of a new Targa 50 that if their boat is lifted they have to 'throw a switch' or the external metal work becomes 'mains live'. Apparently, this is a Fairline 'feature'.

Really? Surely not. Anyone know anything about this?

 

[prv]

Possibly some weird misunderstanding of earthing?

Pete

 

[David2452]

Does it have an isolation transformer? some, particularly Victron require a bridge installed or switch to be thrown on the IT when the vessel is ashore to maintain the Protective earth, nothing to do with the vessel builder, Fairline or otherwise. What he is being told may be correct(ish) subject to equipment installed.

 

[kashurst]

Thats plain nonsense - why would the metal work become live when it's out of the water. If the metal work is connected to the live at all I suspect he would have had a bit of a tingle by now.

Ask him if he fitted the sky hooks to the cabin roof before the lift out, and has he got the long weight to go with them?

Edit. Honestly does this guy really believe this to be true ?

Edit - sorry but I'm still laughing

Later edit -- sorry Piers if this was a bit harsh, I just had this image of a targa 50 being lifted out, then as the last tip of propeller leaves the water all the hand rails glow blue like a tron movie whilst making a dangerous humming sound

 

[jrudge]

Completely correct.

Fairline run earth to the metal parts of the boat below the water line. If there is a fault the current runs to earth - i.e. the water.

If the boat is lifted you activate earth bypass that breaks this connection. If they did not do this then if there were a fault the shafts could become live.

This is a feature of the Glendinning Cable Master on my boat, so not a Fairline feature per se, just how it is done.

Love the way so many people say it is total rubbish! Dangerous stuff following advice like that. Its all in the manual.

 

[kashurst]

Re the isolation transformer - a switch to join the two earths either side of the isolation transformer would be a good idea as once the boat is out of the water and shore power applied, the boats mains electrics will not be earthed at all. When its in the water the boat is electrically earthed via the anodes into the sea. Maybe this is what our friend with the new Targa 50 is doing? However even if he didn't do it the handrails etc won't become live and the boat will have an RCD fitted too so he's quite safe - well safe from an electric shock anyway.

 

[jfm]

It's a misunderstanding on the part of the guy who told you this. I have this on my boat. The shore power goes thru a proper isolation transformer, which is a proper way to build a boat. The earth circuits in the boat earth to the P bracket or a hull plate. Therefore, unavoidably and perfectly correctly, the earth circuits are not connected by copper to the shorepower earth, but if the boat is OOW that means there is no earth at all. To cure this, there is a big switch in the e/room or somewhere and you close it to join the boat's earth to the shorepower earth, when the boat is OOW. There is a little red light on the dash/panel to tell you this switch is closed - reminding you to open it once you are back in the water, so that you again become completely isolated (in the sense of no copper connection) from the dock and other boats in the marina

This is not a Fairline issue; you get it on any boat with a proper electrical isolation transformer system installed (as opposed to a mere "galvanic isolator" or whatever you call the inferior alternative)

 

[jfm]

Completely correct.

Fairline run earth to the metal parts of the boat below the water line. If there is a fault the current runs to earth - i.e. the water.

If the boat is lifted you activate earth bypass that breaks this connection. If they did not do this then if there were a fault the shafts could become live.

This is a feature of the Glendinning Cable Master on my boat, so not a Fairline feature per se, just how it is done.

Love the way so many people say it is total rubbish! Dangerous stuff following advice like that. Its all in the manual.

Erm you're sort of along the right lines but not exactly correct on the circuitry, and it has absolutely nothing to do with the Glendinning. When out of water, you make a connection not break one. See kashursts post and mine immediately below it (sorry kashurst, I worte my post before seeing yours; we are 100% agreeing )

 

[kashurst]

Glendinning cable master

The glendiining cable master is just an electric wind-up reel for the shore power cable. In order to wind the cable on to a rotating drum and maintain electrical contact there will be slip rings on the spindle with contacting brushes otherwise the cable wouldn't last very long. When the boat is in the water, a good electrical earth is maintained via the anodes so if there is a mains fault the boat is earthed. However when the boat is out of the water the boats earth to shore power is via a slip ring contact - this is probably not acceptable to the various testing authorities who would want to see something more substantial. Thats why there is a switch to make sure a boat with Glendinning style drums and or isolation transformers are properly earthed when ashore. Again though modern boats have RCD fitted so in the event of an electrical fault shore power will cut out in milliseconds earth or no earth. Again though the handrails etc won't become "mains live".

edit sorry JFM was writing whilst you posted

 

[jfm]

The glendiining cable master is just an electric wind-up reel for the shore power cable. In order to wind the cable on to a rotating drum and maintain electrical contact there will be slip rings on the spindle with contacting brushes otherwise the cable wouldn't last very long. When the boat is in the water, a good electrical earth is maintained via the anodes so if there is a mains fault the boat is earthed. However when the boat is out of the water the boats earth to shore power is via a slip ring contact - this is probably not acceptable to the various testing authorities who would want to see something more substantial. Thats why there is a switch to make sure a boat with Glendinning style drums are properly earthed when ashore. Again though modern boats have RCD fitted so in the event of an electrical fault shore power will cut out in milliseconds earth or no earth. Again though the handrails etc won't become "mains live".

edit sorry JFM was writing whilst you posted

K, what you write above isn't correct re Glendinning. I have two of them and am intimate! They do not wind onto a drum (at least not at my 2x 100 amp size; I dunno about megayachts). Instead, they force the cable to curl inside a big dustbin rather like a snake before the snake charmer has enticed it out. The cable twists as it does this of course. Accordingly there are no slip rings and there is just a hard wired connection

The reason for this mystery switch therefore has nothing to do with a slip ring via an earth and classification societies. Indeed, as you correctly wrote in your earlier post the shorepower cable earth is redundant and doesn't connect to the boat's earth circuit at all. You could chuck it away and have no earth in the shorepower cable, EXCEPT when the boat is OOW then you throw the switch and connect the boat to the dock earth via the shorepower cable

 

[kashurst]

The smaller versions do wind on a drum - however yours sounds a much better solution I will have to look that mechanism up.

 

[jfm]

Ah yes I see. I have 2x CM 8s. Can handle 42mm dia cable though my cables are around 30mm. Of course, the thicker your cable the warmer the weather you want for this thing to work well, because it prefers the cable pliable than stiff!

In the pic below the drum looks quite small; mine are 2x this size. Also the shiny tube leading to the external/transom lid is short in this pic; in my boat these tubes are 4m long, from transom to e/room. The microswitch on top of the tube, a few inches from the transom lid, is opened by the shorepower plug and so turns the winder motor off automatically once the cable is fully reeled in. Very nice stuff

Seems quite heath robinson way to handle a cable but they are remarkably good. With the 4 I've had there has never been any problem at all. I love them

 

[DougH]

For a full explanation from an actual manufacturer see Energy Solutions www.energy-solutions.co.uk and look for the ES DOCKPOWER product.

I have a full system fitted and find the product first class in quality and operation.

Not sure if it is the same product that is fitted by Fairline.

 

[jfm]

For a full explanation

Hmm, not so sure Doug. That machine is dealing with something different (even though it uses isol transformers) and there is zero explanation on ES's website that is relevant to Piers' original Q.

This particular Energy Solutions product has always struck me as not one of their better inventions. I don't have one because their maximum size is 60 foot ish. Fairline generally don't fit them. It does of course do exactly what is says on the tin, if you are prepared to devote 620x620x450mm to it, which is getting on for a washing machine. But the problem is this: in the Med generally and perhaps in many other places you rarely get given 2 shorepower sockets. Sure, you might get lucky off season and have no boat in the space next to you, but generally that isn't the case. If you only have one shorepower socket at your berth, this large ES box is a total white elephant. The isolation transformer part of it still saves you from electrolytic corrosion which is nice, but you can have that with a much smaller isol transformer.

If I missing something and there is actually an advantage to one of these commensurate with its size, do please tell! You say you like yours - are you saying you often get a berth where you can plug in both your shorepower leads, to two different sockets???

EDIT - Doug maybe you meant "ES isolation transformer" not "ES Dockpower"? Then your post makes perfect sense. Yes these are the same ones that Fairline fit - I have two of the 24Kva versions on my boat

 

[Piers]

It's a misunderstanding on the part of the guy who told you this. I have this on my boat. The shore power goes thru a proper isolation transformer, which is a proper way to build a boat. The earth circuits in the boat earth to the P bracket or a hull plate. Therefore, unavoidably and perfectly correctly, the earth circuits are not connected by copper to the shorepower earth, but if the boat is OOW that means there is no earth at all. To cure this, there is a big switch in the e/room or somewhere and you close it to join the boat's earth to the shorepower earth, when the boat is OOW. There is a little red light on the dash/panel to tell you this switch is closed - reminding you to open it once you are back in the water, so that you again become completely isolated (in the sense of no copper connection) from the dock and other boats in the marina

This is not a Fairline issue; you get it on any boat with a proper electrical isolation transformer system installed (as opposed to a mere "galvanic isolator" or whatever you call the inferior alternative)

Hi jfm. Being a little baffled by this, the question I find myself pondering is why isn't the "P bracket or hull plate" connected to the mains earth to save having to throw a switch?

 

[Bertramdriver]

Love the tingle. My boat is earthed through a metal plate above the keel. Ashore I have to fix an earthing lead from the steelwork into the ground otherwise visitors climbing aboard on a metal ladder get a 12 volt AC tingle. Free ECT!
This only happens when shore power is connected.

 

[kashurst]

Hi Piers
the hull plate, P bracket anode etc are all electrically connected together so they individually and collectively act as an electrical earth into the sea. (usually the anode as it doesn't get blathered with antifoul). The anodes now have two roles
1) galvanic protection for the boats metal work
2) electrical earth when 240V ac is present on board the boat and in the water
When a boat is connected to shore power without an isolation transformer, the shore power earth is connected to the boats' earth. In isolation this is OK as the marina earth and sea earth should be at zero electrical potential. However all the other boats and all the steel work in the marina are also connected to this same earth and ultimately to your anodes. If a near neighbour has dodgy anodes then there is a chance your anodes will start to work to protect his boat and yours and they will disolve rather rapidly leaving you unprotected from galvanic corrosion.

If you simply disconnected shore power from your boat to shore then this cannot happen and your anodes only work with your metal work. But you have no shore power.

If you have an isolation transformer you can earth the transformer to the marina earth and you can earth the boat through your anodes but there is no direct electrical connection between your boat and the marina - so no neighbours disolving your anodes and no risk of electrical shock. But when the boat is out of the water the boat has no earth connection at all - so the switch is used to temporarily join marina earth to the internal boat earth.

Now there is another way to earth a boat and avoid excessive anode disolving - fit a galvanic isolator. This is four diodes in the earth connection from the shorepower earth to the boats earth. This effectively breaks the link between shore power earth and boat earth for voltages less than @ 1v. Galvanic voltages are typically less than 0.5V so it is not possible for your neighbours boat to use your anodes and your boat is still connected to either the sea when its in the water or marina earth when its ashore. No switch, no transformer, simple.

An isolation transformer does have another advantage - it solves the potential problem of reversed live and neutral on shore power connections. However with the majority of 240V power stuff on boats and houses it actually doesnt matter which way around they are - if you look at appliance plugs in Europe and the US you can put them in either way around. The serious potential issue is if you have a generator on board you must have a double pole isolation switch from the generator to the boats 240V circuits when on shore power. Because generator neutral is usually connected to the boats earth.

Isolation transformer or galvanic isolator - they are both a compromise, JFM wants total isolation and a seawater earth, I am happy with sufficient galvanic separation and a seawater earth (whats the difference?). However I trust my anodes to protect the props and my life to the Residual Current Detector because most marina wiring after years of sea air can be a bit shonky

 

[kashurst]

Hi BertramDriver
If you are getting a tingle thats not good - sounds like something on board is on its way out, or the shore power earth isn't! (see previous post)
You might want to try isolating the various 240V kit on board and see if the tingle stops.

 

[jfm]

Hi jfm. Being a little baffled by this, the question I find myself pondering is why isn't the "P bracket or hull plate" connected to the mains earth to save having to throw a switch?

You mean connected when in the water, or connected when oow?

When in the water, you do not want it connected for all the reasons kashurst gives. you want the only earth on your boat to be the sea, and not a copper stake driven into the ground (which is what the shorepower earth is). If you use the shorepower earth, your boat's metal work is connected to your neighbour boat's metal work (via the dock earth wires) and you have a nice battery/galvanic cell in which your metalwork might just happen to be the anode and the other guy's the cathode, which means yours will fizz away (The reason you might be the anode as opposed to the cathode could be a fault on the neighbour boat or just the fact his metal is more noble than yours)

When OOW you do want your boat's earth circuit connected to the dock earth. You could get an auto jump lead and connect one end to your hull plate/anode/P bracket and the other end to the dock earth or to a copper stake in the ground, but that is EXACTLY what closing the "big fairline switch" does

 

[kashurst]

Im just being frivolous really but BertramDrivers tingle problem has got me thinking. What ever the cause of BDs tingle, the shore power earth is not working. Either BD has a problem on board and some electrical kit is leaking electricity to earth or the shore power lead is not earthed and something else is leaking into that. However if the problem is on BDs boat a good earth would stop any tingle and probably blow a breaker. So I think BDs shore power earth is bad and he has been very wise to create his own.

Bearing this in mind here is a good "what next skipper":-

I'm not so sure having a big earth join switch to link boat earth to marina earth is such a good idea really. At first glance the boat is immediately earthed directly to shore power so all in theory is good. However there is a problem..
You know from use that your own boat is electrically safe as you have been using it in the water - so if it had a fault to boat earth, the circuit breakers or RCD would be tripping out. Assuming they are all OK then your boat is electrically OK and you are quite safe, earth or no earth.
Now lift the boat out of the water and connect to a strange shore power connection. You don't know if that is safely earthed. Chances are staff in the yard have used it for power tools etc but they will be double insulated etc and they won't know if its earthed properly either. You would hope that all the marina electrics are periodically tested. Now, if for instance our friend with the Targa 50 goes to a marina with a dodgy earth, gets a lift out and plugs into the shore power, closing the earth link switch could be the last thing he ever does!

By not closing the switch you are at risk from your own boat - which you know is OK, if you close the earth link switch you expose yourself to a potentially unknown risk, that doesn't have a circuit breaker or an RCD inline to save you.

So what should you do? (sorry I'm a bit bored today, waiting to go the boat tomorrow so feel free to ignore)