burgundyben
Well-Known Member
If there was a major current leakage in the water in a marina, within what radius would boats be affected?
Current leakage - radius affected?
- Thread starter burgundyben
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William_H
Well-Known Member
No answer and that is not surprising. The concept of current leakage from one boat affecting another is very uncertain to say the least. Firstly because the current is most likely AC but then often AC going through contacts of different metals can produce a rectifier effect to produce more +ve or -ve curret than a simple ballance you might expect.
Then you would have know just where the current is flowing in the water. Is it to a mains system earthing stake on land (or inm the water) and is your boat anywhere near that path?
Or are you concerned witha DC leakage from another boat. More likely to cause problems with that boat than another. So who knows?
If you are or think you ar ehaving problems with electrolkysis and loss of metal in your under water gear then a first step might be to disconnect mains connection. If you don't want to do that, do you have a mains earth connected to your ships earth. If so a galvanic isolator might stop the small currents that cause electrolysis.
My club insist on a GI for all boats having an earthed mains earth on the boat or 24/7 mains power hook up. The implication being that leakage current can affect nearby boats. (no idea of range of affect)
So the whole subject is a very black art. good luck olewill
Then you would have know just where the current is flowing in the water. Is it to a mains system earthing stake on land (or inm the water) and is your boat anywhere near that path?
Or are you concerned witha DC leakage from another boat. More likely to cause problems with that boat than another. So who knows?
If you are or think you ar ehaving problems with electrolkysis and loss of metal in your under water gear then a first step might be to disconnect mains connection. If you don't want to do that, do you have a mains earth connected to your ships earth. If so a galvanic isolator might stop the small currents that cause electrolysis.
My club insist on a GI for all boats having an earthed mains earth on the boat or 24/7 mains power hook up. The implication being that leakage current can affect nearby boats. (no idea of range of affect)
So the whole subject is a very black art. good luck olewill
burgundyben
Well-Known Member
I do have shore power on board, its not connected all the time, only when we stay on board overnight which has been 11 days this year.
She's been in the water 2 months and a pair of perfectly good props are trashed. Something has changed this year, I've re-engined the boat and there might be a failing in the bonding.
Oddly, there's a shore power socket on the pontoon that's not working.
She's been in the water 2 months and a pair of perfectly good props are trashed. Something has changed this year, I've re-engined the boat and there might be a failing in the bonding.
Oddly, there's a shore power socket on the pontoon that's not working.
Tranona
Well-Known Member
Think you have answered your own question. You need to check out the anodes and connections - but even then props corroding in 2 months suggests something is seriously wrong with your boat.
burgundyben
Well-Known Member
There is definitely something seriously wrong.
But I haven't answered the question, if there was a problem boat or pontoon electric cable, how far away could it be?
I can check out all the anode bonding and make good, I have a meter, less than 0.3ohm is my target. Surveyor says there maybe a cause other than a weakness in the bonding.
But I haven't answered the question, if there was a problem boat or pontoon electric cable, how far away could it be?
I can check out all the anode bonding and make good, I have a meter, less than 0.3ohm is my target. Surveyor says there maybe a cause other than a weakness in the bonding.
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lw395
Well-Known Member
Has there been a lot of anode erosion, or is it just the props suffering?
burgundyben
Well-Known Member
I went down with a meter tonight. Anode bonding to the p brackets and rudders is fine, bonding to engines and hence the shafts and props had failed, fixed that.
Seems to be no current drain through batteries or bilge pump.
Maybe that was the cause, I think I'll re-launch once props are fixed and jump in once a week to check visually.
Seems to be no current drain through batteries or bilge pump.
Maybe that was the cause, I think I'll re-launch once props are fixed and jump in once a week to check visually.
savageseadog
Well-Known Member
To answer the original question. The leakage current field would look a bit like this:
burgundyben
Well-Known Member
To answer the original question. The leakage current field would look a bit like this:
Thanks, very interesting, but it doesn't show distance. I guess the amount of current leaking and salinity are the two major factors, but I don't really know.
savageseadog
Well-Known Member
Yes it's complicated, and that's without a boat or pontoons in the way. At one time I could have done the calculations but it was a while ago. It's a lot easier to set up some experiments or just measure what's there.
burgundyben
Well-Known Member
I did find last night that my engine anode bonding had failed. So I re-made all those connections. I got readings of 0.3 or 0.4 ohms on my meter between anode and shafts (hence engines, all in direct contact), P brackets and rudders, so all the main components.
My meter reads 0.3 ohms when you contact the probes, so I thing getting 0.3 or 0.4 is fine.
I have no current draw with battery banks off and no draw with them on but nothing switched on.
No current draw through the bilge pump wiring with the float switch down (and as you's expect with the float down there's no continuity)
So maybe having fixed the engine anode bonding I wont have a problem.
My meter reads 0.3 ohms when you contact the probes, so I thing getting 0.3 or 0.4 is fine.
I have no current draw with battery banks off and no draw with them on but nothing switched on.
No current draw through the bilge pump wiring with the float switch down (and as you's expect with the float down there's no continuity)
So maybe having fixed the engine anode bonding I wont have a problem.
VicS
Well-Known Member
My first thoughts were that loss of two props in such a short space of time would not be due to "stray currents" or galvanic corrosion but rather due to electrolysis as the result of an onboard electrical wiring fault or defect.
Hopefully your check on current draw have eliminated that. You checked for current right down to the mA range I hope.
There an outstanding possibility of something occurring when the bilge pump operates . That is if it does often operate automatically. There is something in the back of my mind, as you might guess, something that happened to another forumite with disastrous consequences.
Be sure all your bonding is quite independent of any wiring that carries current and that there is no way the bonding can carry any DC load current.
superheat6k
Well-Known Member
I found an earth leakage following Nigel Calder's advice. You are looking for really low level current flow.
Disconnect the positive terminal from the battery bank then with the isolator on and all services off connect the VM between the positive terminal and disconnected lead end. If there is no leakage at all the meter will read 0. Even a few milliamps will cause a voltage reading.
If this happens you then have to start disconnecting circuits to identify where the leak is occurring, but start with the obvious, which is the bilge switches / pumps
Mine turned out to be a duff bilge pump float switch serving the engine bay.
In the end I found the following all contributing to high port side anode wear ...
1 Neutral - Live reversal in shorepower lead
2 No GI
3 Used an LED as a Neutral to Earth polarity indicator - big mistake as this effectively and completely bypassed the GI for its first season
4 Leaky float switch
5 Poor bonding connection to the barely worn starboard anode.
I now also use a pair of part worn 4kg bar anodes on a stainless wire dangled over the pontoon side when on the home berth and connected into the bonding circuit. This last year allowed me to re-use the stbd anode, and the port was less than half worn for the first time, although I did swap this as a precaution.
burgundyben
Well-Known Member
Thanks for taking the time to comment.
All bonding is independant of wiring that carries current (although of course there is continuity via the blocks and the main starter earth leads and others). I.e. I could remove all bonding wiring and all other systems on the boat would remain complete and working.
I'm fairly sure there id no way the bonding can be carrying current.
Having fixed the engine bonding, she's going back in with shaft anodes too.
I'll go for a weekly swim under to visually check on things, if problems persist I'll invest in a silver chloride reference cell (albeit I'll have to work out how to use it and interpret the results).
VicS
Well-Known Member
Take a look at http://www.galvatest.com/ if you are thinking of going for a Ag/AgCl electrode.
Its been plugged on here by a forumite (with vested interest ) in the past but might be what you will need to test and interpret the readings.
burgundyben
Well-Known Member
Thanks Trev and Vic.
burgundyben
Well-Known Member
Here's a pic of the prop nut, perfectly good nut to this in 2 months.
VicS
Well-Known Member
It worries me that it can deteriorate so quickly, that it is something which is new and has occurred after re-engining the boat. Hopefully fixing the defective anode bonding will have sorted it
but
I think I'd want to find an underlying cause ...... I am sill thinking, despite all your checks, of an onboard defect or fault, causing electrolysis.
Hopefully Vyv will see the picture and have some contribution ........ He''ll likely want the picture for his website !
Should have asked sooner but do you know what material the props ( and nuts) are
lw395
Well-Known Member
If the anodes are not destroyed, they are either not bonded to the props effectively, or are too far from the props.
If the anodes are destroyed, then I suspect you have current flowing into the boat.
Is there anything else which is more cathodic than the props?
e.g. a big lump of stainless?
If you have a big lump of stainless bonded to your props, the props are prone to being an anode for the stainless, unless you have lots of zinc closer than the props.
Hence shaft anodes are a Good Thing.
If you have shore power, disconnect it and carefully measure the voltage between the shore power 'earth' and a copper wire dipped in the sea, using a high impedance meter.
If the anodes are destroyed, then I suspect you have current flowing into the boat.
Is there anything else which is more cathodic than the props?
e.g. a big lump of stainless?
If you have a big lump of stainless bonded to your props, the props are prone to being an anode for the stainless, unless you have lots of zinc closer than the props.
Hence shaft anodes are a Good Thing.
If you have shore power, disconnect it and carefully measure the voltage between the shore power 'earth' and a copper wire dipped in the sea, using a high impedance meter.
vyv_cox
Well-Known Member
Those are my thoughts too. For corrosion to have taken place at that rate, and with general pitting as shown in the photo, I suspect there is a voltage driving it. It bears comparison with the known connection of underwater parts to the positive side of the battery, although this was a direct connection in which the damage occurred within two weeks (or until the battery was flat) http://coxengineering.sharepoint.com/Pages/Electrochem.aspx