galvanic isolator

[mike e]

Hi everyone

I recently had a hull survey done on my narrow boat Thanfully it was sound,but the surveyor mentioned slight galvanic damage and recomended fitting a gavanic isolator to prevent further damage. I can understand how they work when you are connected to shore power But do they work when you are not, do you still get damage from others around you that are. I also use when needed, a standard car battery charger to top up the batteries and was informed that these can cause galvanic damage So is the answer to this to disconnect the battery and charge direct from shore power

 

what do other forum users think

 

 

mike e

[mayalld]

Hi everyone

I recently had a hull survey done on my narrow boat Thanfully it was sound,but the surveyor mentioned slight galvanic damage and recomended fitting a gavanic isolator to prevent further damage. I can understand how they work when you are connected to shore power But do they work when you are not, do you still get damage from others around you that are. I also use when needed, a standard car battery charger to top up the batteries and was informed that these can cause galvanic damage So is the answer to this to disconnect the battery and charge direct from shore power

 

what do other forum users think

 

 

mike e

 

If you aren't connected to shore power a GI won't do anything.

 

However, if you are using a car battery charger then you ARE connected to shore power (and if you are charging from an extension lead from the shore, rather than from a shoreline that is properly bonded to the hull, you really shouldn't be)

[blackrose]

I also use when needed, a standard car battery charger to top up the batteries and was informed that these can cause galvanic damage So is the answer to this to disconnect the battery and charge direct from shore power

 

what do other forum users think

 

 

mike e

 

No, that part is all nonsense. Running a battery charger has noting to do with galvanic corrosion.

 

I can understand how they work when you are connected to shore power But do they work when you are not, do you still get damage from others around you that are.

 

I think it is theoretically possible for a boat to suffer from galvanic corrosion even if it's not connected to shore power, if it's situated between two boats that are on shore power and are not galvanically isolated. But as Mayalld says, in that circumstance a galvanic isolator would do nothing to protect your boat.

Edited October 30, 2011 by blackrose

[mike e]

No, that part is all nonsense. Running a battery charger has noting to do with galvanic corrosion.

 

 

 

I think it is theoretically possible for a boat to suffer from galvanic corrosion even if it's not connected to shore power, if it's situated between two boats that are on shore power and are not galvanically isolated. But as Mayalld says, in that circumstance a galvanic isolator would do nothing to protect your boat.

[mike e]

Thank you

for your replies it looks like i should invest in a GI for the times that I do connect to shore power allthough i would yhink i only connect to shore power for about 2hrs per week . And in future i will connect the battery charger through the boat rather than direct from the shoreline.

one more point why are so called marine chargers alot more expensive than a bog standard car chargers

 

 

thanks again

mike e

[blackrose]

Thank you

for your replies it looks like i should invest in a GI for the times that I do connect to shore power allthough i would yhink i only connect to shore power for about 2hrs per week . And in future i will connect the battery charger through the boat rather than direct from the shoreline.

one more point why are so called marine chargers alot more expensive than a bog standard car chargers

 

 

thanks again

mike e

 

If you're only connected to shore power for only 2 hours/week then I wouldn't even bother with a GI. I have one because I live aboard and I'm connected permanently.

 

A proper 3 stage (marine) battery charger can be left on permanently and will not damage your batteries. Many bog standard car chargers can't do that. The other thing is that marine chargers start at 10 or 20 amp output whereas car chargers are generally lower output. However a small good 3 stage charger doesn't have to cost the earth. There's another current thread somewhere on the forum where someone is buying a 10 or 20 amp 3 stage charger for about 50 or 60 quid!

 

Bargain! Unfortunately it's no longer available. But there must be others out there.

 

http://www.ebay.co.uk/itm/FULLY-AUTOMATIC-MARINE-BATTERY-CHARGER-12V-20A-/130476404657?pt=UK_CarsParts_Vehicles_BoatEquipment_Accessories_SM&hash=item1e60ffefb1#ht_1068wt_905

Edited October 30, 2011 by blackrose

[Dominic M]

 

I think it is theoretically possible for a boat to suffer from galvanic corrosion even if it's not connected to shore power, if it's situated between two boats that are on shore power and are not galvanically isolated. But as Mayalld says, in that circumstance a galvanic isolator would do nothing to protect your boat.

Forget "theoretically." It is certainly possible. I had a 10 year old boat on brokerage 2 years ago. It had no 240v system at all. When it was taken out of the water for survey, there was very serious galvanic corrosion. This had to have been caused by a neighboring boat in the marina where it had spent most of its life. No GI will protect against that.

Edited October 30, 2011 by Dominic M

[blackrose]

Forget "theoretically." It is certainly possible. I had a 10 year old boat on brokerage 2 years ago. It had no 240v system at all. When it was taken out of the water for survey, there was very serious galvanic corrosion. This had to have been caused by a neighboring boat in the marina where it had spent most of its life. No GI will protect against that.

 

I guess if that's true then the only answer would be to move the boat. The trouble is that identifying galvanic corrosion isn't easy - how many people are qualified or experienced enough in aspects of ferrous metal corrosion to know the difference between the many different types of corrosion?

Edited October 30, 2011 by blackrose

[JDR]

 

 

one more point why are so called marine chargers alot more expensive than a bog standard car chargers

 

 

thanks again

mike e

If you unplug your car battery charger but leave it connected to a battery the charger will still be drawing power from the battery (albeit at a very low level).My understanding is that the expensive chargers must include transformer coils to isolate the battery from the charger and prevent it being backfed allowing it to be hardwired permanently to the bank.If you find a reliable 30A charger that can be permanently connected let me know.

 

If you unplug your car battery charger but leave it connected to a battery the charger will still be drawing power from the battery (albeit at a very low level).My understanding is that the expensive chargers must include transformer coils to isolate the battery from the charger and prevent it being backfed allowing it to be hardwired permanently to the bank.If you find a cheap reliable 30A charger that can be permanently connected let me know.

[theguitardoctor]

Forget "theoretically." It is certainly possible. I had a 10 year old boat on brokerage 2 years ago. It had no 240v system at all. When it was taken out of the water for survey, there was very serious galvanic corrosion. This had to have been caused by a neighboring boat in the marina where it had spent most of its life. No GI will protect against that.

 

That's slightly worrying...what circumstances would cause that...something the neighbouring boat was running...? Was that boat also cursed with Galvanic Corrosion..?

[bizzard]

I worked on a 12'6''wide/beam boat in dry dock during the summer. It has inside powerful mains appliances,ie Washing machine,tumble dryer,washing up machine,micro-wave, powerful hi-fi equipment,massive tele,electric fire towards the front ect ect.Most of these things were down one side,and ''EXACTLY!'' where they are is really serious electrolosis pitting,also the propeller and rudder were badly zapped.It had a correctly fitted galvanic isolator.

I also had to renew stern-tube bearing and remount and align the engine as it was hopelessly out of alignment.

All this on an 4 year old boat with about 250 hrs on the clock. I suggested that if he wanted to continue running all that stuff,to get a wooden boat.

[mike e]

I worked on a 12'6''wide/beam boat in dry dock during the summer. It has inside powerful mains appliances,ie Washing machine,tumble dryer,washing up machine,micro-wave, powerful hi-fi equipment,massive tele,electric fire towards the front ect ect.Most of these things were down one side,and ''EXACTLY!'' where they are is really serious electrolosis pitting,also the propeller and rudder were badly zapped.It had a correctly fitted galvanic isolator.

I also had to renew stern-tube bearing and remount and align the engine as it was hopelessly out of alignment.

All this on an 4 year old boat with about 250 hrs on the clock. I suggested that if he wanted to continue running all that stuff,to get a wooden boat.

[mike e]

Thanks everyone

thank you all for your replies, my boat is not permanently connected to shore power at most for 24hrs for a battery re-charge or a day on the mooring.I am not surrounded by boats that are on shore power although i am moored next to a large marina I suspect most of the damage was caused by the previous owner who used it as a live-aboard connected to shore power. Although i am still undecided about fitting a GI

[ditchcrawler]

Thanks everyone

thank you all for your replies, my boat is not permanently connected to shore power at most for 24hrs for a battery re-charge or a day on the mooring.I am not surrounded by boats that are on shore power although i am moored next to a large marina I suspect most of the damage was caused by the previous owner who used it as a live-aboard connected to shore power. Although i am still undecided about fitting a GI

Not on shore supply means completely disconnecting the cable, not just switching the power off.

[mike e]

Not on shore supply means completely disconnecting the cable, not just switching the power off.

 

Yes

unpluged power lead stowed

[blackrose]

I worked on a 12'6''wide/beam boat in dry dock during the summer. It has inside powerful mains appliances,ie Washing machine,tumble dryer,washing up machine,micro-wave, powerful hi-fi equipment,massive tele,electric fire towards the front ect ect.Most of these things were down one side,and ''EXACTLY!'' where they are is really serious electrolosis pitting,also the propeller and rudder were badly zapped.It had a correctly fitted galvanic isolator.

I also had to renew stern-tube bearing and remount and align the engine as it was hopelessly out of alignment.

All this on an 4 year old boat with about 250 hrs on the clock. I suggested that if he wanted to continue running all that stuff,to get a wooden boat.

 

Although RFI from some mains appliances could have forced the diodes in the GI to go into circuit, I don't understand what relevence the positioning of mains equipment inside the boat would have on pitting on the hull?

[nicknorman]

Although RFI from some mains appliances could have forced the diodes in the GI to go into circuit, I don't understand what relevence the positioning of mains equipment inside the boat would have on pitting on the hull?

I was wondering the same. I suppose a single "live" wire gives off an alternating magnetic field that could induce current in the hull, causing galvanic corrosion, but normally a cable has equal and opposite currents in the L and N conductors that would cancel out the magnetic field.

[theguitardoctor]

Wow, I am confused now...!!

 

It seems that if you spend most of your time in a marina, connected to a shoreline 240V feed, then effectively you are dissolving your hull at a rapid rate, even with a Galvanic Isolator...??

 

Even if you only connect for one day a week, then inevitably your boat will corrode before your eyes....!!

 

I don't hold much hope for my prospective boat as I can only cruise at weekends due to work committments, and in December I work 7 days a week, so even that is compromised.....

 

Seriously...what can you possibly do to evade this corrosion? I thought regular blacking, anodes and a GI would do the job....

[bizzard]

Although RFI from some mains appliances could have forced the diodes in the GI to go into circuit, I don't understand what relevence the positioning of mains equipment inside the boat would have on pitting on the hull?

Nor me but that's how it was.I just welded new anodes on that side next to those areas.I couldn't put any on the other side as at 12'6'' wide the boat would jamb in certain locks on the R.Stort. I expect i'll see the results the next time its docked.

[bizzard]

Also a friend of mine with only simple mainly 12v electrics was moored breasted to a 70' boat behind me,When he docked his boat for routine blacking ect discovered pretty horrendous electrolytic activity and pitting in a certain patch on his starboard forward area.later i discovered that the boat behind me which he was breasted to had installed a mains central heating pump exactly on that the side and position of my friends boats pitting,needless to say its one of those boats that never ever moves.

My friend now moors away from it.

[bigcol]

Off course they work!!!!

 

Simple test that was done on our boat and neighbours boats

 

Here we are plugged in 24/7

 

I had a new A new wide beam never been in the water, launched 2009, didn't go anywhere really, but a year and a half later it was taken out for survey as I had sold it.

 

The amount of pitting in just a year shocked me and my neighbours, at the same time we were talking to a surveyer and a qualified electrician, who carried out a simple test, as one of our neighbours boats produced a lot of air type bubbles a bit like a aspirin in a glass.

 

I'm not a electrician, but he Put a

1) meter one end to the shell and one to the mooring ring with the boat connected to the mains and it reg 6.1 stray volts

2) done the same test, but disconnected the shore line and hardly nothing!

 

The test surprised us all and went down the line of boats carrying out the same tests and different degrees of results but all showed stray current

 

My neighbour that day got hold of a Gavonic isolated and had it fitted ,

 

Carried out same test

 

With or without shoreline connected. Measured hardly anything! And no fizzing bubbles

 

Over the next week a total of 4 of us had GIs fitted

 

Of course if your moored next to someone that's plugged in and with no GI I imagine your boat is still going to attract stray current from him.

 

It be interesting if somone here on the forum done the same simple test, and confirm his results. Please as it's a simple 5 minute test but with sup rising results

 

There are more expensive galvanic transformers which you can buy from £400 but a Gavonic isolator you can buy for around £75

 

They work Gavonic isolators stop stray current which helps you stop electrolisis, stray current, and damage to your hull through pitting

 

Big ships use a transformer system but in a grander scale

[bizzard]

A few years ago i made some friends in Stoke-on-Trent,and they told me that no one much bothered about having Anodes fitted at all around there,as no ones boat ever suffered from it,mind you these were towpath moorers with simple 12v electrics,also as many of you will know,the water around there is rich in the red oxide from old mines and from Sheldon steel works which was opposite them,now closed down i believe.Maybe this oxide,rusty water somehow absorbed any electrolytic activity. bizzard.

[bizzard]

So nip out everyone and buy up all the red oxide you can and pour it all in your canal-river and whack loads of it on your hull instead of the black stuff.

[bigcol]

Another observation Was that I happened to be around when a boat got craned out last week.

 

Nice folks, constant cruiser,, don't have 240v at all, just a genie, very rarely plugged in to shore power, 1990s boat, owned the boat for 12 years, hadn't been out for a long long time,

 

yet no pitting,!!!

 

Liverpool boat, must be a good hull?

 

Col

Edited November 1, 2011 by bigcol

[bizzard]

Another observation Was that I happened to be around when a boat got craned out last week.

 

Nice folks, constant cruiser,, don't have 240v at all, very rarely plugged in to shore power, 1990s boat, owned the boat for 12 years, hadn't been out for a long long time,

 

yet no pitting,!!!

 

Liverpool boat, must be a good hull?

 

Col

I'm told that a lot of hire boat companies don't bother with them as their boats are on on the move for most of the time,and most only have low powered electrics. Wooden boats will become all the rage with ''elec- power- happy'' boaters.