Galvanic Isolation

[Ray]

Gimmick? Essential? Somewhere in between?

My boat came with a GI unit externally mounted on the outside of the transom. It's ugly and I'm going to remove it.

At a pinch I could open the case and use the components inside it as an inline device somewhere near the consumer unit.... But I'd rather not bother!

New anodes were fitted a month ago. At a very basic level I understand what it does but with an anode do I need it?

[BrundallNavy]

Depends where you moor, when I bought Nipper I was moored in a shed with around 60 boats most on shore power, at the back of my mooring there was a steel key heading within 6 months half my rudder had disappeared.

Along with a new rudder and anodes fitted a Galvanic Isolated and had no further problems. 
 

 

[eddybear]

Personally I would say no you don't need it, as long as when the boat is lifted to anti-foul etc and your anodes are checked and replaced as necessaryyou should be okay Assuming your boat is lifted every two years and anti-fouled It's probably a good idea to replace the anodes They are not callled sacrificial anodes for nothing 

They can vanish before your eyes in very salty water

 

[Ray]

Thank you... it seems to be yes and no depending on the circumstances and conditions of mooring then. I guess that's as expected.

Will remove it I think then maybe have a look at putting it somewhere else as part of winter tinkering, I mean maintenance.

[Polly]

Sorry in advance!! I wondered if this was anything to do with Covid ( actually no, I didn’t but it’s an interesting concept). Sorry Ray!😊

[Cheesey69]

well, I had a boat moored in the Medway. Lost the anodes, The prop shaft pitted like mad, and the bronze prop de zinced.

Your trusting the marinas and your neighbours have not got any leakage from their 240 or 12 volt.

Are the wire connections in the power post clean? if not stray milliamp voltage needs to find its way back.

And the more salty the water, the conductive it is.

Anti foul has nothing to do with it. you have metal swimming in a low grade battery. It forms a conductive bond with your engine and back to neutral.

[Cheesey69]

so we turned off the battery isolators, disconnected any power drains before the switch and measured any current flow across the terminals. 

its going to be measured in the milliamp range and mine was high. Disconnecting the alternator stopped it, a leaking diode.

This is stray current corrosion and in pure salt water can do real damage but less so here.

so make sure your 240 is isolated from the rest of your boat and keep your plug clean. an isolator can be a belt and braces approach. 

[Ray]

I like a belt and braces approach to things 👍

[thunder]

"essential" keep it mount it inside never did understand why it was fitted on the transom.

personally I would change it for an isolation transformer, but a gi is better than nothing,

[BroadAmbition]

Fitting a GI is far cheaper than replacing shaft / Rudder / prop etc. I would opt for essential as you can’t rely on neighbours boats being leak free

Griff

[ExSurveyor]

Had a GI fitted for 9 years here and previously 7 years on the medway. Both exhire boats that don't have annodes fitted. Never had any issyes to the metal work.

[annv]

Hi Ray i would advise fitting it in side before connections to the consumer unit, This is more important now as more and more boats have mains power connected.  also to get protection on a glass fib a boat ALL metal items in contact with the water need a wire connection to the galvanic isolator, the prop needs a carbon brush cont-actor to get the protection, anodes also need a wire connection to all metal items in contact with the water or have a anode them bolted to each item, often only rudder has this. ,PREVENTION is much cheaper than cure/replacement. John

[Ray]

Thanks John, I will move it rather than remove it. I guess as I have one and as it can clearly be useful it would be a bit daft of me not to fit it 👍

[Polly]

Sounds right to me.

[floydraser]

This subject has been raised again around our marina and one of the next jobs I have to do is replace the old 240 shore power socket on my boat. I'm now thinking it may be a good time, while I'm messing with the very wires where a GI would go, to fit one.

My questions:

Is size important? I see various sizes available

Would the girls be impressed by the size of my galvanic isolator? "Hi, would you like to come aboard and I'll show you my galvanic isolator. It'll make your eyes water!" 

[Ray]

As above my boat came with one bolted to the outside of the transom! Preferring to maintain my air of mystery until at least the second date I moved it inboard in case anyone "came back for coffee" 😁 

I've had no complaints about size!

[floydraser]

Safeshore do a 70amp or a 100amp for instance. I can't find a guide to how to chose a suitable size for the boat.

Would a steel hull need the higher rating? 

[Ray]

Sorry, I got carried away and didn't answer properly. I hope this helps -

"15 amps, 30 amps, 70 amps, 100 amps? What does it mean?

A question we are asked all the time. Basically the amperage rating of the isolator is the amount of current the isolator can handle under severe fault conditions. The isolator must be able to handle more than the available current supplied to the boat. Usually UK marina supplies are either 16 or 32 amps so the isolator must be able safely handle at least 20% more than the maximum current available to comply with legislation. Realistically the higher the rating the more reliable the isolator."

[floydraser]

6 hours ago, Ray said:

Sorry, I got carried away and didn't answer properly. I hope this helps -

"15 amps, 30 amps, 70 amps, 100 amps? What does it mean?

A question we are asked all the time. Basically the amperage rating of the isolator is the amount of current the isolator can handle under severe fault conditions. The isolator must be able to handle more than the available current supplied to the boat. Usually UK marina supplies are either 16 or 32 amps so the isolator must be able safely handle at least 20% more than the maximum current available to comply with legislation. Realistically the higher the rating the more reliable the isolator."

And as Michael Caine would not say, "There's not many people know that!".

[grendel]

galvanic isolation, is that what you have to go through when you catch a nasty case of the corrosion's, does it last 10 days?

[Smoggy]

1 hour ago, grendel said:

galvanic isolation, is that what you have to go through when you catch a nasty case of the corrosion's, does it last 10 days?

I told you not to lick the handles of galvanised shopping trolleys, don't post it on youtube or it might go viral.

[floydraser]

Well I think I have to be happy with this. I have no finacial interest here but hope this helps anyone searching this subject in the future.

https://www.ebay.co.uk/itm/182802256088?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2648

It came with some fittings and a bit of earth wire, along with ten pages of literature including fitting instructions. I went for the 70amp version which is advertised at £69 but this was £48.45 delivered from the manufacturer's own Ebay shop. Not much for peace of mind I would say?