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Shaft grounding / bonding


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Why? you want to create a circuit to get the electrolysis going? 

 

If you haven't got electrolysis don't touch it.

Ah, well. Because the boat had a system when I bought it.. but its pretty crappy / broken, so I thought I should re-do it.

 

And Its been not / poorly connected for a while and I ate through a shaft anode to near nothing in 18 months..

 

XtsMsFF.png

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Did the Anode last longer with the grounded shaft?

My shaft isn't grounded, I painted my shaft and prop put a new anode on and got problems, the paint blistered off, the anode disappeared real quick and I got Oysters growing on the shaft and prop. Bit of research led to the conclusion I was over protected, these were all the classic signs. I left the anode off and all is now happy, the anode actually made a very nice battery and caused more trouble than it solved. Two boat builders I spoke to at the time also suggested leaving the anode off. I was a bit nervous initially but a year later, with regular inspections to ease my mind, all is well.

Years ago I worked with a consultant who specialised in anode protection of boats, he often mentioned problems caused by over protection ( too many  anodes), there are some good papers on the subject. I think having the prop and shaft well painted my help too, lack of surface area for electrolyte to work on. I actually suspect its a factor in many stories of real expensive propspeed applications failing rapidly, the current induced by the anode "lifts" the paint off. The accepted wisdom of needing an anode on the shaft sells a lot of anodes and the fact you are sticking them on a dissimilar metal guarantees some action which is then presented as proof they were needed, nice little racket.

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BOIGuy Firstly, Paint or any coating will NOT stop electrolysis.
Secondly, over anode will not cause the anode to disappear faster. In fact it slows right down to the extreme of turning white.
Any two dissimilar metals connected together in at water creates a battery. Hence why the Zinc is called an anode.
Bonding the shaft/prop is essential. If you don't, then the first thing that will happen is the dezincification of the prop.
Isolated Shafts can be bonded two ways. Either by a brush system as shown or by an earth wire connecting the two halfs of the coupling together. Or thirdly, leaving it isolated and fitting it's own zinc.
With out proper testing, I cannot speculate on what was happening

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18 months is pretty good for an anode. Wear can depend on where you are moored ,marina could get other vessel leaching attacking your anode. Hence why made of zinc and are sacrificial,its doing it job.

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Wiring the two coupling halves together can work however it will tend to cause any currents present to flow through your gearbox bearings which is can be a bit of a problem. 

Pretty sure painting a zinc will stop it working, try making a battery with the anode and/or cathode sealed with paint. Think of it as preventing contact with the electrolyte. 

With out proper testing, I am quite happy to speculate on what was happening.

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BOIGuy ????‍♂️

 

Is ‘Big Marine Electrical’ joining ranks with ‘Big Oil’ and ‘Big Pharma’?

 

None of the boat builders in my area have an electrolysis tester, therefore, don’t really know what is happening to a particular boat. Do the boat builders have electrolysis testers where your from? Do they go to the boat and test before lifting it out? And again a month or so after relaunch to see what’s happening? That’s what I do. As an electrician. The local boat builders seem to work on the idea ‘it’s all witch craft, and we’re scared or witch craft’.

 

You can’t make a proper determination just by looking at the boat once lifted, only a best guess, something major and obvious aside. You need routine electrolysis tests to get a thorough picture over time. Sure, if you have a major issue, you can pick it up with one test and fix it then retest.

 

Don’t need to bond the shaft? What if the only anode on the boat is on the shaft? Don’t bond the shaft, making the anode last longer, by allowing your engine to erode away? That sounds like a great option, new motors are cheaper than new anodes. Right? If only they made some small, cheap sacrificial metal thing to erode rather than the motor.

 

Electrolysis is already happening, flowing THROUGH THE WATER, that’s what it is. Bonding makes everything sit at the same voltage, like a battery with all the negative plates removed. No current will flow.

 

Winter, yip, that’s what I normally use. Bend it to have enough tension to make good contact, but not too much or they can scream when the motor runs. Check tension regularly.

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Electrolysis is already happening, flowing THROUGH THE WATER, that’s what it is. Bonding makes everything sit at the same voltage, like a battery with all the negative plates removed. No current will flow. 

 

So if I bond everything together I wont need an anode because everything sits at the same voltage? Not a very good explanation me thinks.

 

In order to have electrolysis you need an anode a cathode and an electrolyte, if you remove one (think insulation) you dont get a battery. If you have no battery and add a zinc you will have a battery

 

With out proper testing, we continue to speculate on what was happening.

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Boiguy that is not what MM said. If you bond it all, one anode can be used. If you dont, you should have an anode on everything that has more than one type of metal. Bet you dont.

Different metals, electrically connected, then in seawater, will corrode. It's a battery.

Worse than that is stray current corrosion. I've seen the bottom half of a saildrive completely gone in a few months. Proper checks as above would have prevented this. Every boat should be checked, using the right gear, at least every year. I do my own one 2x a year. The test will show over/ under anode protection, and any stray current issues. It is very much more time consuming on an improperly bonded boat.

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BOI, you have only half the story. There are two very different issues you are confusing together. Galvanic Corrosion and stray electrical Currents. Galvanic corrosion is due to a current being created between tow dissimilar metals. Stray electrical currents are caused by electrical leakage and improper Earthing. Both have the same result, but are two very different causes.
    There are two ways to attack Galvanic corrosion. Either bond or isolate. Any two metals connected to one another and submersed MUST be protected via an anode. With some larger vessels, there maybe many metals exposed to the Saltwater. Such as bronze skin fittings and especially if it is a Steel Hull for instance. In this instance it is common for all fittings to be bonded together and one Zinc protects them all. In some instances like Fglass hulls, Bronze skin fittings are left completely isolated and only the shaft/prop and associated parts are connected to an anode.
   By the way, in some instances, electrical current can work right through paint. It depends on what the paint is as to how insulative it is. But the main concern is when the paint is damaged.
   In relation to another post comment, Anodes should last no longer than a year as a rule of thumb. Any longer and the anode may be too large to begin with.
  
Slightly aside, Aluminium Anodes have never been discussed on Crew as far as I know. They are well worth considering as they last longer, are cheaper and in fact can provide better protection.

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Thank you, I do understand the different types of corrosion. I think you may have finally realised my point about paint being an isolator.

As to  stray currents, if you have them and then bond an otherwise isolated prop / shaft or anything else  to the item that is then immersed it is not going to be good. Get rid of the stray current, don't go and pass it through an otherwise innocent part.

I would like your opinion on what to do when you have an isolated shaft / propellor with one anode that is obviously overprotected, the current i.e.induced by the anode is way more than needed. 

I think that blindly advising people to bond it all together an stick an anode on is a liitle bit dangerouse and certainly has caused many problems that might not have been there in the past to many boaties, as you may realise, there is quite a bit more to it.

https://www.anodeoutlet.co.uk/symptoms-of-over-cathodic-protecting/

https://littleshipclubcanterbury.wordpress.com/2015/05/21/mysteries-of-electrolysis/

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I don’t think anyone here has told you to blindly bond and stick on an anode. And you should totally disregard anything from anyone who talks about electrolysis.

It’s either galvanic corrosion or stray current corrosion. There are several posters here that make a living with marine electrics.

It’s important to protect any part of the vessel with different metals in contact and immersed. As said above a single type of metal fitting can be ignored, if it is completely isolated, in most cases.

When setting up a boat, or working out what to use, the use of a silver silver chloride electrode to measure the protection is mandatory, otherwise it’s a guess.

Paint is not a reliable insulator.

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BOI, you have only half the story. There are two very different issues you are confusing together. Galvanic Corrosion and stray electrical Currents. Galvanic corrosion is due to a current being created between tow dissimilar metals. Stray electrical currents are caused by electrical leakage and improper Earthing. Both have the same result, but are two very different causes.

    There are two ways to attack Galvanic corrosion. Either bond or isolate. Any two metals connected to one another and submersed MUST be protected via an anode. With some larger vessels, there maybe many metals exposed to the Saltwater. Such as bronze skin fittings and especially if it is a Steel Hull for instance. In this instance it is common for all fittings to be bonded together and one Zinc protects them all. In some instances like Fglass hulls, Bronze skin fittings are left completely isolated and only the shaft/prop and associated parts are connected to an anode.

   By the way, in some instances, electrical current can work right through paint. It depends on what the paint is as to how insulative it is. But the main concern is when the paint is damaged.

   In relation to another post comment, Anodes should last no longer than a year as a rule of thumb. Any longer and the anode may be too large to begin with.

  

Slightly aside, Aluminium Anodes have never been discussed on Crew as far as I know. They are well worth considering as they last longer, are cheaper and in fact can provide better protection.

Aluminium Indium anodes work well on alluminium hulls, and they last.

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Ah, well. Because the boat had a system when I bought it.. but its pretty crappy / broken, so I thought I should re-do it.

 

And Its been not / poorly connected for a while and I ate through a shaft anode to near nothing in 18 months..

 

XtsMsFF.png

We have always had a flexible coupling and have never grounded / connected it. We have a zinc on the shaft, which we replace every 6 to 12 months. Other than the engine pencil zincs, its the only anode on the whole boat.

We haven't had any issues with the shaft with regards anodes. When we brought the boat there were wires connecting / bonding all sorts of things together. What we did find was major issues with over-protection that caused the ions to be pulled out of the wood, meaning soft mushy wood (Double Kauri with a glass skin). That meant some serious timber repairs.

Only issue we had with the shaft was necking / scouring at the packing gland, and pitting on the tapper, which is to do with the type of stainless (316) and lack of oxygen. We replaced it when we did our engine overhaul last year, with a posh and expensive new 4 digit stainless (5066 or something?), mainly because of the necking at the packing gland, and I wanted a slightly longer shaft to accommodate a posh new flexi coupling to the engine.

 

I don't see the issue with an anode lasting 12 months or less. They don't cost much, and its two allen screws to install / remove. As others have said (Lateral etc) I'm a fan of simple systems. Over complicating it with bonding etc has actually caused problems for us in the past.

 

Disclaimer, I haven't actually read or the BS back and forth above on the finer points of everything, the purpose of my post is just to say what we do, and what happened when everything was over complicated (from the previous owner), which I think is relevant to winter's case.

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Winter, we seem to have all been slightly distracted from your original post. Was it answered for you?
The strap with the Carbon brush on the end is common and you should be able to get another one from a Marine sparky no problem. The carbon brush on the end is usually a Silver/Carbon or Copper Carbon material.
The picture of the shaft does give me one concern however. The Brush looks like it may be home made. Nothing wrong with that if it is working. However, normal practice is the earth wire should connected directly to the Carbon brush itself and not a ways down the strap like the Picture seems to show.

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Winter, we seem to have all been slightly distracted from your original post. Was it answered for you?

The strap with the Carbon brush on the end is common and you should be able to get another one from a Marine sparky no problem. The carbon brush on the end is usually a Silver/Carbon or Copper Carbon material.

The picture of the shaft does give me one concern however. The Brush looks like it may be home made. Nothing wrong with that if it is working. However, normal practice is the earth wire should connected directly to the Carbon brush itself and not a ways down the strap like the Picture seems to show.

somewhat. If I want to replace I can use a brush like the one pictured, (taking care to attach my wire directly to the brush).

OR

I can remove the bond entirely, as my shaft and prop have an anode, and my engine has 3 internal anodes, so there would appear to be no real need to join them.

 

Im going to replace the brush with a new one. seems to have worked ok in the past so Ill just fix up and tidy without reinventing the system here..

 

thanks to all for the advice and reading material.

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Sounds good. Keeping the brush could allow you to do away with the shaft anode. Those things are not cheap. But you have to ensure the main anode is connected to that earth wire so all is protected. if in doubt, keep the shaft anode.
Should you ever be over protected, there is a good tell tale sign. The Anode will get a white crust on it's surface and will not eat away.
The small pencil zincs inside the engine cooling units etc are protecting in a different way. The main anode on the Hull will not protect those parts. So ensure you replace them. Even though they are silly expensive, the cost of those cooling units make you eyes water
 

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