Paranoid about Galvanic action...?

[Mako]

Like most of us steel and ferro boat owners, one of the things about my (ferro) boat which worries me most of all is what I can't see- boat cancer.

I want to check things over to make sure I'm doing what I can to ensure the effects of galvanic action are minimised and that my boat is correctly grounded. The way I see it I first need to know if I have a problem - then I need to deal with it, and put into place regular checks to keep on top of it.

I guess the first thing is to identify how my boat currently stacks up on that front. About 18 months ago the boat was left for about 12 months without anode protection. I would turn low amp items on and they wouldn't necessarily go -including lights, radios etc. They went sometimes and not at others. Immediately I replaced the anodes and replaced the vast majority of the boat's wiring with tinned cable (as the cables had gone black on the negative side), and that seemed to fix the problem. The anodes now run out -correctly- about every six-eight months, and I replace them- and things all seem to work correctly. But has longer term damage been inflicted where I can't see it?

One of the radio's seems to suffer from interference for about 30 minutes after a DC appliance such as the pump get's used, then it returns to normal. That just started happening out of the blue about 8-9 months ago. If it has been on a while, the problem worsens, and doesn't need another appliance to be turned on to suffer from 'interference'. Of course its not interference- it just sounds like it-, it's possibly a grounding issue -which I don't know how to quantify or resolve.

I have noticed around the engine block, where the grounding circuit connecting underwater fittings makes contact, that it appears to have more rapidly corroded in the last 9 months or so. The rest of the engine block is perfectly OK. The manifold I suspect may be corroding faster than it should judging by the fact I've recently had to replace the steel flange and pipe fitting between the waterlock and the manifold because it had almost completely corroded. I've now included this previously isolated fitting in the ground circuit to try and reduce galvanic effects, but the manifold I'm less sure about, and the corrosion around the engine block mounts where the ground circuits join, worry me a bit.

Can anyone who's been down this road make comments on what to look for and how to judge if there is a problem- I'm currently thinking things like connections, the grounding circuit itself, measuring for galvanic action (but how?) etc would be things to look at but I'm not really that sure on where to start. Size of ground circuit cable, where the cable should run, things to spot, how to measure etc, if anyone has feedback I'd be interested to hear.

Thanks,
Mark.

 

[chippie]

It seems to me that you are monitoring things fairly well. I think that if there was a problem with the armature of your ferro boat you would see pronounced rust weeping and a degree of 'blowing' of the plaster around any faults.

Just keep monitoring things and take action as required. (I am assuming you will keep anodes etc. up to scratch).

Cheers

 

[ccscott49]

I would add, ensure there are no high resistance joints anywhere in your galvanic circuit, where it bolts to fittings, coorosion around fittings, will cause high resistance and the anodes will not protect that item, clean all connections, tighten, then seal with silicon grease, ensure all wires are not black and if they are replace with tinned copper as you have on some circuits, monitor the rest as has been said.

 

[AndrewB]

This does feel a bit paranoid - or you have a big problem. I'm not particularly careful about galvanic protection, changing the anodes every couple of years or so is about it. But apart from slight pitting of the steel hull near to the propellor, after 15 years there are no obvious problems around the hull. The real problems I have, like most steel boat owners, are where aluminium fittings and steel come into contact, at window frames, mast etc.

The black rot in cables I thought was the result of sea-water entry rather than electrolysis. Soulds like your terminals need better protection. While concentrated at terminals it can spread along, and would certainly explain your poor connections. Through the black conducts, it is brittle.

My yacht avoids a negative earth. Everything, including the engine block, is isolated from the hull. This may help.

 

[ean_p]

I'd go with Andrew on that....keep the various systems isolated including use an isolating trasformer for the shore supply and try to relax.......

 

[Sinbad1]

Re: Its easy.

First you have to understand that there is a difference between the two types of galvanic action that affects boats.

1. Stray current corrosion. This is where you have a leak of electricity either from one of your 12/24v circuit or via the AC shore power system. In simple terms you just fix the wiring!

2. Electrolysis. This is what most of us are talking about when we mention galvanic action. It is the effect of having disimilar metals in a saline solution which allows the small electrical difference between the metals to set up an electrical current between them. The effect of this current is to errode one of the metals.

Now as we have a number of disimilar metals in the briny on our boat (stainless shaft, bronze prop, steel hull) we avoid the important bits being erroded by this small electrical current by placing a metal that errodes more easily than the boat metal, ie, a big zinc anode, in the vicinity of the metals we wish to be protected.

To be really effective the zinc which is to be sacrificed (hence sacrificial zinc) has to be connected 'electrically' to the other metals. Having the zinc physically attached to the part to be protected is a 100% way of ensuring this connection but wouldn't help your prop if you had a 10lb zinc swinging around on it. So what we do is place the zinc near the important metals and connect wires from the zinc to the parts that are underwater and need protecting.

Ok, thats the theory at its simplest. You have bits of metal being protected by this zinc or zincs. You now need to check that the whole system is working correctly. Go to B&Q and buy a digital multimeter with long leads and a big readout screen. Turn it on and set the dial to ohms 200. You will have a reading of 1. This is infinite resistance. ie no electrical current is travelling between the two metal probes of the machine. Touch the two metal probes together and the reading goes to 000. A perfect connection and this is what you want on your boat.

With your boat out of the water place one of the probes on the zinc and the other probe on the hull (steel). Reading should be 000. Then same on prop, shaft etc. A perfect electrical connection between them is 000. and this way your zinc will do its job.

This isn't rocket science, its simple and logical.....and in a wierd kinda way, fun as you now know something that many boatyards haven't a clue about.