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Post by Clinton Cool on Dec 4, 2016 22:58:52 GMT
I've read a couple of horror stories where people's hulls have almost disappeared before their eyes, without them seeing it. Not wanting to suffer the same fate I'd like to ask a few questions:
If you're out on the cut, moving around, are you pretty well immune from this?
Is it only shoreline 230v that causes this, or can the 12v from your batteries do the same job?
Does running a generator a couple of hours a day during winter whilst out on the cut put you at risk?
Cheers
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Post by Deleted on Dec 4, 2016 23:06:46 GMT
I've read a couple of horror stories where people's hulls have almost disappeared before their eyes, without them seeing it. Not wanting to suffer the same fate I'd like to ask a few questions: If you're out on the cut, moving around, are you pretty well immune from this? Is it only shoreline 230v that causes this, or can the 12v from your batteries do the same job? Does running a generator a couple of hours a day during winter whilst out on the cut put you at risk? Cheers Can I interest you in some magnetic anodes sir? My latest invention. The adults will be along shortly to give you a sensible answer. Whilst you are waiting, however, there is some useful info on the smartgage website if you haven't already seen it :- www.smartgauge.co.uk/galv2.html
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Post by Telemachus on Dec 4, 2016 23:07:17 GMT
Yes
Mostly only shoreline (the earth connection thereof) but a badly installed DC system that uses the hull as the return path can also do it.
No. it is connecting the shore-based mains Earth (that may not be at local Earth potential) to the boat's hull that can cause the problem.
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Post by Clinton Cool on Dec 4, 2016 23:21:28 GMT
Yes Mostly only shoreline (the earth connection thereof) but a badly installed DC system that uses the hull as the return path can also do it. No. it is connecting the shore-based mains Earth (that may not be at local Earth potential) to the boat's hull that can cause the problem. Cheers, that's quite reassuring. Not that it was keeping me awake at night but I do like to learn... Regarding the hull/ return path. I think the hull should be negatively charged, or act as an earth, the other way of looking at it. I have a thick negative wire from the batteries to a stud on the engine, I guess this makes the whole hull negative. Is it that individual circuits should return to the batteries via dedicated negative wires rather than relying on the overall negative nature of the hull, is that it?
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Post by Telemachus on Dec 4, 2016 23:27:47 GMT
It's not really that the hull should be negatively charged - it isn't, since the positive is just "floating". It's more to do with fault detection to avoid the hull being connected to +ve without you realising. If the hull is deliberately connected to -ve and then there is a fault that connects the hull to +ve, the fuse blows. Exactly what is "wrong" with having the hull connected to +ve I can't remember, but it is explained on the Smartgauge website and certainly something to do with corrosion.
Yes, it is that the individial circuits should return to the battery via dedicated negative wires and not by flowing through the hull.
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Post by davewally on Dec 5, 2016 0:46:41 GMT
At our last blacking we had some slimline anodes fitted at the centre of the boat. I haven't seen them since our boat was back in the water before I saw it.
Dave
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Post by Deleted on Dec 5, 2016 6:56:07 GMT
At our last blacking we had some slimline anodes fitted at the centre of the boat. I haven't seen them since our boat was back in the water before I saw it. Dave I was considering the same but advised they would probably get knocked off.
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Post by Deleted on Dec 5, 2016 7:00:41 GMT
Side mounted anodes do get knocked off. I have found two in locks with the magnet.
I picked them up by the steel weld tag at the end.
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Post by Deleted on Dec 5, 2016 7:02:52 GMT
Side mounted anodes do get knocked off. I have found two in locks with the magnet. I picked them up by the steel weld tag at the end. Ah, magnetic anodes with GPS location tracking, there's an idea
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Post by JohnV on Dec 5, 2016 8:13:38 GMT
In very simple terms There are several different types of corrosion the one you most hear about is electrolytic corrosion caused by stray electrical currents either from fault conditions in the boats wiring or caused by a difference in voltage between the "Earth" supplied by your shore electricity supply and the "Earth" supplied by the water you are floating in. The other type that you put anodes on to help protect is galvanic corrosion which basically is .... if you have two diferent metals joined together that are also in water, you have in effect a battery and the current flow from that battery can be sufficient to eat away the metal. You put anodes on the steel in the hopes that these metals will have a higher voltage difference to the hull and all it's attatchments and will sacrifice themselves instead there are also srange other forms of corrosion that can occur. This subject is another boating subject that is a black art, with many twists and turns. Sufficient to say it is so specialist, that there are very few who profess to understand all about it.......best treat it like black magic. a good simple explanation here mgduff.co.uk/cathodic-protection
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Post by lollygagger on Dec 5, 2016 10:12:19 GMT
Sooooooo....
I have a galvanic isolator with lights to show AC or DC problem. I noticed when I blacked it had it blacked that there were a few bright slightly pitted areas which must be galvanic corrosion. They are all around the middle of the boat, as far from the sacrificial anodes as could be. I'm hooked up to ac mains in a marina.
What could be the cause?
Edit: I don't have a transformer, I have a galvanic isolator.
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Post by Deleted on Dec 5, 2016 10:46:09 GMT
Sooooooo.... I have a galvanic isolator with lights to show AC or DC problem. I noticed when I blacked it had it blacked that there were a few bright slightly pitted areas which must be galvanic corrosion. They are all around the middle of the boat, as far from the sacrificial anodes as could be. I'm hooked up to ac mains in a marina. What could be the cause? Edit: I don't have a transformer, I have a galvanic isolator. How do you determine if your GI is protecting your boat 24/7?
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Post by lollygagger on Dec 5, 2016 11:01:09 GMT
Sooooooo.... I have a galvanic isolator with lights to show AC or DC problem. I noticed when I blacked it had it blacked that there were a few bright slightly pitted areas which must be galvanic corrosion. They are all around the middle of the boat, as far from the sacrificial anodes as could be. I'm hooked up to ac mains in a marina. What could be the cause? Edit: I don't have a transformer, I have a galvanic isolator. How do you determine if your GI is protecting your boat 24/7? Sit and watch the lights? I don't know!
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Post by Deleted on Dec 5, 2016 11:07:02 GMT
How do you determine if your GI is protecting your boat 24/7? Sit and watch the lights? I don't know! Maybe you could extend the LEDs to your christmas tree. I would have thought, but have no expertise,as you can probably tell, that an audible warning would be more useful. (Scurries back to mancave to invent audible GI/IT type thingy)
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Post by JohnV on Dec 5, 2016 11:09:21 GMT
The trickling sound of water running through a corrosion hole ?
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