Electrolysis effecting billfish action

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Post Options Post Options   Likes (0) Likes(0)   Quote shaneg Quote  Post ReplyReply Direct Link To This Post Posted: 11 Sep 2021 at 11:09am
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Have been following this with interest. Am a believer that electrical current combined with vibration emanating from hull is a fish spoiler when trolling especially for billfish. Unfortunately a view formed by experience and frustrating few years fishing after replacing my motor. To compound matters have always found understanding electricity, volts, amps difficult. Can operate a battery charger, don’t really know how to work volt meter purchased. Have been told by service guy not to do any more wiring of accessories as last effort might have caused a fire.
Anyway when we went from old f50 yamhi to new suzuki, we/ they fitting motor , didn’t replace the very thin nylon backing plate, we have subsequently had motor taken off and a very thick nylon backing plate installed on outside on transom. This has I think improved strike rate, although last few season saw us only catching a few yellowfin but at least getting odd marlin strike again.
Another thing we have done is fit more stainless rod holders to boat over the years, and a few years ago prior to new motor going on put a very heavy duty stainless rocket launcher on after original stabicraft alloy one disintegrated. There is certainly a lot more stainless on boat than used to be, most of it partially insulated with that foam pad stuff but not where bolts actually go through alloy.
The stabicraft hull however while 20 years old, has virtually no visible corrosion apart from a little around painted topside where original fittings for nav  lights are attached. Unpainted hull and pontoons have no corrosion at all.
Hoping for better results and return to the good old days this coming season.

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My scorpion has a fibreglass cabin so all of the electrics and rocket launcher mounted off that, other rod holders are plastic. But I have seen a lot of things like radio Ariel cables wear through, the outer part of the coax cable is earthed to the radio and when it wears through this will earth the radio to the hull.

Just checked mine yep voltage between the hull and battery with isolate switch off, just a few milliamps which will be from the issues from earlier post. Leakage from dirt buildup just like you get across your battery terminals when the top of your battery is dirty.
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Great subject.
I think I have my own problems around this, still investigating hence my interest.

A couple of things I've noticed in posts.

Checking current between battery pos terminal to hull.
Not sure that is helpful to determine leaks with battery isolator switch off.
If you think that through it's not a necessary valid test.

Krow points to using the bus bar, from the positive to well what should be the neg bus bar with isolator switch off.
Now that makes sense to me and is the test I would do.

I have had a boat that completely isolated the engine from the pod. Somewhat expensive. Though I did it at the time for harmonics.

bigfishbob. Was there a particular reason for a teardrop shaped anode or just a recommendation to use an anode.

Another question that has occurred to me is some of my tech requires grounding, this is different to a negative grounding.
So is this grounding in an alloy boat to the hull of a seperate form of grounding.
Just cruising in my now sweetas pimped out Southern 755 HT0!
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Originally posted by MATTOO MATTOO wrote:

Great subject.
I think I have my own problems around this, still investigating hence my interest.

A couple of things I've noticed in posts.

Checking current between battery pos terminal to hull.
Not sure that is helpful to determine leaks with battery isolator switch off.
If you think that through it's not a necessary valid test.

Krow points to using the bus bar, from the positive to well what should be the neg bus bar with isolator switch off.
Now that makes sense to me and is the test I would do.

I have had a boat that completely isolated the engine from the pod. Somewhat expensive. Though I did it at the time for harmonics.

bigfishbob. Was there a particular reason for a teardrop shaped anode or just a recommendation to use an anode.

Another question that has occurred to me is some of my tech requires grounding, this is different to a negative grounding.
So is this grounding in an alloy boat to the hull of a seperate form of grounding.


The pos busbar is connected to the battery pos be it directly from the battery or from the motor depending on the outbourd. The neg busbar is connected isolation switch which is normally on the neg side so by connecting the metre between the pos of the battery is connecting the metre effectively in the same way. Connecting a metre across both busbars with the isolation switch on is the same as connecting the metre across the pos and neg of the battery, turn the switch on you will read voltage turn it off you won’t.

What we are testing for is a connection of some type be it direct or by leakage to the hull. Outboards are neg earth so we connect between the battery pos and hull. If the battery is to hard to get to, yes as krow said you can use the pos busbar with the other side of the metre to the hull. So but just connecting a metre across the battery will not indicate any leakage.

Marine electronics have a pos and neg lead/wire that you run back to the busbar/fuse box be it through switches or not, so I wouldn’t expect yours to be earthed directly to the hull.
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Bigfishbob keep an eye on that anode as the bolts may cause corrosion to the hull. I had this issue. 
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Originally posted by Kandrew Kandrew wrote:

Yep this is right the battery switch should completely isolate the battery, so things don’t sound right. Can you see if any electrical works or if the starter with the battery switch off.

If you want you can PM me your number and I’ll give you a call.
It makes perfect sense to me that I would get battery voltage by going from battery + to hull.  As Krow states. The battery + is looking for an earth to ground to. The hull is a large block of metal. Perfect earth. Isolating sw on or off should not make any difference here?
But I will check tomorrow at a +Ve bus connector and hull with isolating sw off. Should be zero - or mV.
I think the trick is not to get a connection between your hull and the engine earth system. This will operate while the + circuit is live throughout the boat - isolating sw On. 
I installed 3 teardrop anodes in the hull about 8 yrs ago - worried about corrosion. Yes - some of the stainless bolts have frozen to the hull. But then I have stainless bolts all over the boat - incl the motor mounts. Dunno how you avoid them.
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Alan

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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 11 Sep 2021 at 6:39pm
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I will do a test tomorrow - on the + bus connection and hull, Isolating sw off. It should be zero mV. Any mV recorded will be an indication of the boat hull acting as a battery with the dissimilar metals. I think this is the more pertinent test. Any electrochemical difference connected via the hull will show up in that result.
As per an earlier Q, the shape of the anodes really is irrelevant. I put teardrop ones in because thats what I could source that would go where I wanted them. The key is they are zinc. More reactive than Al. Thats all you are trying to achieve really. The shape has no bearing. They come in all shapes and sizes and do the same job. I use big zinc blocks in my cray pots. They are probably near 20 yrs old now. Replaced the anodes once in most of them.
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Originally posted by Alan L Alan L wrote:

Originally posted by Kandrew Kandrew wrote:

Yep this is right the battery switch should completely isolate the battery, so things don’t sound right. Can you see if any electrical works or if the starter with the battery switch off.

If you want you can PM me your number and I’ll give you a call.

It makes perfect sense to me that I would get battery voltage by going from battery + to hull.  As Krow states. The battery + is looking for an earth to ground to. The hull is a large block of metal. Perfect earth. Isolating sw on or off should not make any difference here?
But I will check tomorrow at a +Ve bus connector and hull with isolating sw off. Should be zero - or mV.
I think the trick is not to get a connection between your hull and the engine earth system. This will operate while the + circuit is live throughout the boat - isolating sw On. 
I installed 3 teardrop anodes in the hull about 8 yrs ago - worried about corrosion. Yes - some of the stainless bolts have frozen to the hull. But then I have stainless bolts all over the boat - incl the motor mounts. Dunno how you avoid them.
Regards
Alan


Yep I agree only if the battery switch is turned on just remember Alan this is a DC 12V so there is technical only a pos and a neg no earth The only way the current can flow and a volt metre can read is when a connection is made between the pos and neg, if the neg is disconnected by turning the isolation switch off the voltmeter will not read. The neg battery cable comes from the battery to the isolation switch first then from the other side of the switch to the engine so when the switch is turned off it’s like disconnecting the battery there should be no connection. It should be the same if you connect the voltmeter straight across the battery pos and neg then lift one of the voltmeter clips off the neg, no volt reading turning the isolation switch off should do the same thing. Turn your lights on and off same thing, sorry mate not trying to sound condescending just trying to explain things.

This is the problem there is a very small amount of leakage to the hull which could be as I’ve said above could be a wire that’s chaffed through.

The reason I asked if your motor can turn over when the isolation switch is turned off indicates there is stronger connection back to the battery more than just a chaffed wire.
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I have no electrics when my isolating sw is off. My isolating sw disconnects the + side of the feed ONLY.
The earth cycle goes straight to the battery.
So there is a continuous + feed (on) or not (off).
The -ve wire in my system goes nowhere near my isolating sw. Direct from the motor to the battery.
You only need to break one leg of the cycle?
Regards
Alan
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Originally posted by Alan L Alan L wrote:

I have no electrics when my isolating sw is off. My isolating sw disconnects the + side of the feed ONLY.
The earth cycle goes straight to the battery.
So there is a continuous + feed (on) or not (off).
The -ve wire in my system goes nowhere near my isolating sw. Direct from the motor to the battery.
You only need to break one leg of the cycle?
Regards
Alan

Should be no different to above weather the isolation switch is on the pos or neg it should still disconnect the battery but all boats are setup differently.
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Yep - agree. Either or.
In my case it is the +ve that is broken.
Will post some results tomorrow.
Altho the boat is dry right now - windy. It should be worse mV reading in the briny - the transom is partly submerged.
Will do both when I can - hopefully in a few days. Salt water is a great conductor. That is part of the issue. Pure water is a poor conductor. That is why fresh water is not so bad. Not perfect - but better than salt. Deionised water, in theory is a very poor conductor.
I will do both tests over the next few days - depending when I can drop the boat in.
Regards
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Originally posted by Alan L Alan L wrote:

Yep - agree. Either or.
In my case it is the +ve that is broken.
Will post some results tomorrow.
Altho the boat is dry right now - windy. It should be worse mV reading in the briny - the transom is partly submerged.
Will do both when I can - hopefully in a few days. Salt water is a great conductor. That is part of the issue. Pure water is a poor conductor. That is why fresh water is not so bad. Not perfect - but better than salt. Deionised water, in theory is a very poor conductor.
I will do both tests over the next few days - depending when I can drop the boat in.
Regards
Alan  
I must admit I was quite interested in the leakage I measured in my boat, would be interesting to see where it comes from, I have sprayed the back of the isolation switch where the terminals are with lanolin, I wonder if there is a tiny leak across there. I don’t know how conducive that coating is, what do you think?
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Well, my thoughts are based on what I have just measured. Interesting.
I tested the + bus to hull with iso sw Off. I got 4mV. Which is close to zero basically. Then tried the - bus and got less than 1 mV. Now the bus blocks are plastic type insul blocks screwed to the hull. So they seem to be doing their job.
I then thought to try the -ve battery to hull. This is my 'live' circuit - does not go thru an iso sw. Live between motor earth and battery . I got around 1mV. Looking good. But there are a few small corrosion spots on the transom shelf  - I tried there and got around 250mV if I hit the right spot in the right place. There was quite a variation - some more active than others. I then thought to try my zinc block closest to where I was;  400mV.
So, conclusions to date, my zinc blocks are doing what they should do, and.......... I have leakage (potential differences , or voltage produced) in my earth circuit. In answer to your query, I don't see this as a leakage across an iso sw type of thing - but a connection between dissimilar metals. In my case in the earth circuit. Because my motor is earthed to the hull. I think the only way I can reduce this is try and isolate the motor better. That is going to require some thought. How do you bolt a motor to a transom without using bolts?
Back to the OPs original Q, in my experience the voltage produced by my boat is not scaring fish. But at the same time it is producing corrosion, albeit maybe slowly. It would be a win/win to reduce this to as close as possible to zero.
Regards
Alan 

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Interesting talk of isolating the negative of the battery, I think it's the exception not the rule.

As for motors being isolated by their mounts between the motor and the stern bracket, , there are plastic bushes between the tilt bracket and the transom bracket, hence most motors have little stainless eating cables, you find the odd one melted where something has gone wrong and the negative battery lead has had a bad connection on the motor, and a second connection to the hull, the little bonding cable tries to make up for the poor main negative lead..
Some hydraulic steering systems have bonding wired with them, important to use them,
Seen pitting in tilt ram shafts, again, bad bonding .

There should always only be one point where the battery negative bonds to the hull, and that is via the motor. All other negative connections must be made to the battery, or a negative stud/bar which is isolated from the hull.

This is to stop the hull being used as a negative wire in parallel with the actual negative cable.
It's one source of electrolysis.
The other is galvanic electrolysis, which is caused by dissimilar metals in a conductive liquid. You get it between the stainless prop and alloy gearbox, not to mention the possibly bronze washers either side of your prop..
And if the hull alloy is ever so slightly different in composition to the motor castings (will be), then there is a voltage difference between the two metals, and current will flow. Electroplating will then occur. If all dissimilarmetals are bonded by cables, the voltage difference is unable to happen.
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Originally posted by krow krow wrote:

Bigfishbob keep an eye on that anode as the bolts may cause corrosion to the hull. I had this issue. 

I mounted it to the stainless trim tab, so no more new bolts to the hull.
 
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Originally posted by MATTOO MATTOO wrote:

Great subject.
I think I have my own problems around this, still investigating hence my interest.

A couple of things I've noticed in posts.

Checking current between battery pos terminal to hull.
Not sure that is helpful to determine leaks with battery isolator switch off.
If you think that through it's not a necessary valid test.

Krow points to using the bus bar, from the positive to well what should be the neg bus bar with isolator switch off.
Now that makes sense to me and is the test I would do.

I have had a boat that completely isolated the engine from the pod. Somewhat expensive. Though I did it at the time for harmonics.

bigfishbob. Was there a particular reason for a teardrop shaped anode or just a recommendation to use an anode.

Another question that has occurred to me is some of my tech requires grounding, this is different to a negative grounding.
So is this grounding in an alloy boat to the hull of a seperate form of grounding.

TBH, I actually don't know. He simply sugested a 3" tear drop so I did what I was told. We we finaly tested the boat it was bang on. I guess that happens once you've done a few of them.
www.waikatosportfishing.co.nz
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Post Options Post Options   Likes (0) Likes(0)   Quote Alan L Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2021 at 5:20pm
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FWIW I dropped my boat in the briny today - so took my multi meter with me and repeated the measurements I did the day before. Basically same results.
So you can do those checks from the comfort and safety of your own backyard.
Alan
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