galvanic isolator -worth fitting??

[ozzie]

While we were packing up last Sunday we had an interesting conversation with our neighbours. I keep shore power plugged in just for the battery charger, neighbour was advised to keep his turned off when not on the boat. Having done a bit of research I think it would be worth fitting a galvanic isolator as other electrical activity could effect our anodes, and I dont want them wasted in less than a season as has been suggested could happen.
A couple of questions. Do they make a difference, and is it an easy DIY job? I have also seen one on *bay which just plugs into the power point and shorepower lead with no wiring. Any suggestions welcomed, will also pass on to my neighbour!

 

[superheat6k]

Make a difference - Yes; easy to fit - Yes; lead mounted - I would rather have a permanent one - simply wire into the earth lead directly adjacent to the shorepower connection. The rating must match the power supply rating e.g. 16amp. About £70 from the chandlers.

However, switching off AND unplugging completely disconnects you from most stray current problems. The minor risk of this is a water leak occurring and the pumps draining the battery before the leak is discovered.

Note a GI will not prevent AC stray current leaks (from other boats / poor quality marina electrics) damaging underwater metalwork, and contrary to popular belief, AC leakage current can cause underwater corrosion and at a far faster rate than DC galvanic current leakage, which is all a GI will protect against. Fortunately in the UK the rigorous electrical testing regimes do generally reduce marina electrical problems, but these can occur surprisingly easily, which is why I will always retrieve any power lead drooping into the water I see in a marina, being careful not to touch the wetted part.

But please also check for other obvious issues with the boat's electrics ...

No Live / Neutral crossovers on the shorepower lead
Neutral not connected anywhere to earth on the boat (the only exception being at the earth connection of an on board generator and this must be separated from the neutral of the rest of the boat when the generator is switched off
RCD fitted on the boat
No DC leakages through on board fittings, e.g. bilge pump float switches
Bonding connection between the shorepower earth and on board negative / grounding / bonding circuit - note expect a lot of disagreement on this one !

The above list is not exhaustive, and includes some basic safety issues with boat 240vac electrical systems.

Causes and prevention of galvanic and stray current corrosion is quite a subject. Having said all this fitting a GI is well worth while, and will likely stop excessive zinc wastage. If you want some material to read on the subject please PM me.

 

[jimmy_the_builder]

Definitely fit one. Have a search on the forum, this has come up before, lots of discussion about why people fit them.

 

[NoviceRod]

I asked this question when getting our new boat, and there were mixed responses, but generally in favour.

After 12 months:
Prop shaft anode (Volvo end of shaft) completely gone, but no signs of prop or shaft damage. Residue could well have fallen off on way to liftout.
Hull anode and trim tab anodes approx 50% gone

It has no effect on the engine anodes - they seem to last about 6 months.

I am told they are straightforward to fit, but I had it specced into the boat, so cannot be sure.

Hope this helps, no doubt others with more experience will also respond.

 

[Gentlemanracer]

An isolation transformer was the eventual conclusion and solution I adopted in preference to a galvanic isolator. I understood particular reasons why at the time and an IT was a better / more comprehensive solution but now it's fitted, I've forgotten about it, which I remember was one of the benefits! Conclusion, look before you leap, you can only spend it once!

 

[rafiki_]

Definitely worth fitting. I have the plug in version, as mounting the kit permanently looked a bit of a challenge.

 

[l'escargot]

Fitting is straightforward if you have the space, you basically split the earth wire between the input socket and the consumer unit and connect the end of each wire to the GI as in these instructions: http://www.safeshoremarine.com/assetts/diyinstallguide.pdf

 

[jfm]

As mentioned above, there are two alternative devices you can fit: a GI or an isolation transformer. The latter is the Rolls Royce way to do it and results in you being plugged into shorepower but not connected physically by copper wire to the dock. All your electricity supply from shore onto boat comes "through the air" inside the transformer rather than passing along a continuous copper wire. They're quite big things though, so there are practical issues/compromises to consider, as ever. A GI is definitely easier. As mentioned above it's worth searching forum for threads on this in last couple of years

 

[MapisM]

I think it would be worth fitting a galvanic isolator as other electrical activity could effect our anodes, and I dont want them wasted in less than a season as has been suggested could happen.

Just as a FYI, my boat stays in the water at least 7 months/year, with shorepower connected 90% of the time, has no GI, and I never had to replace anodes mid season.
Mind, I'm not against GI by any means, in principle.
In fact, I have half an idea of replacing the battery charger with an inverter, and if I will, quite likely I'll take the opportunity to fit also a GI in the process.
But just saying that no GI doesn't necessarily/always imply catastrophic consequences...

 

[Brightside]

After stray current in our Marina I fitted a GI to my steel cruiser. Very pleased with the results, anodes certainly lasted longer probably 2 or 3 times as long at a guess. The yard were surprised on the last lift when all that was needed was re anti-foul. I am mainly on non tidal Thames so cannot speak for salt/bracken water. However, so pleased that I am about to fit same model of GI to my new fibreglass cruiser. All said, I know people who have used sonic anti foul system and been delighted and others extremely disappointed. No apparent reason/differences. However, for £100 or so IO reckon I have saved that times over. Good luck with what you decide. Best wishes

 

[sharpness]

Fitting a GI has been on my to do list for a while, this post has given me the kick I needed so thanks to the OP for the post. GI ordered and delivery next week. Wiring is a doddle, just a bit of thought needed where to mount it, and another job ticked off the list