Princess P45 Anodes

My boat recently had a couple of trim tab issues and was lifted. One of the two Hull Anodes all but gone, the bow thruster anode all but gone and one of the shaft anodes had fallen off, the other over 50% worn.
Interestingly the rudders are painted stainless steel but a lot of the paint has flaked from one of them. I actually went full on with the anodes. New shaft anodes, fitted rudder anodes, new bow thruster anode and new hull anodes. Not to mention a good check of the bonding and testing for electrolysis etc.

I've also painted the rudders and props (including bow thruster) for added protection, so I'm certainly not taking any chances on corrosion. It's quite a complicated science when you have mixes of bronze, alloy and stainless steel all in 'nice' conductive salt water.
 
Fire99 said:
My boat recently had a couple of trim tab issues and was lifted. One of the two Hull Anodes all but gone, the bow thruster anode all but gone and one of the shaft anodes had fallen off, the other over 50% worn.
Interestingly the rudders are painted stainless steel but a lot of the paint has flaked from one of them. I actually went full on with the anodes. New shaft anodes, fitted rudder anodes, new bow thruster anode and new hull anodes. Not to mention a good check of the bonding and testing for electrolysis etc.

I've also painted the rudders and props (including bow thruster) for added protection, so I'm certainly not taking any chances on corrosion. It's quite a complicated science when you have mixes of bronze, alloy and stainless steel all in 'nice' conductive salt water.
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picture there looks a lovely boat...she a trader ?
 
Fire99 said:
Thanks very much.. Yeah she's a 2002 Trader 47 Sundeck (To give her the full title. :D). She needs some attention after lack of use by the previous owner but I'm happy with her.
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Lovely...always admired any Ive seen.
 
John100156 said:
Interesting and informative many thanks. I am still not 100% convinced so may leave them off next time, after thoroughly checking all bonding systems, to see what impact it may have on main hull anodes - we shall see! Mind you, rather loose some zinc than the props!
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My Azi had prop anodes, but these eroded rapidly and the props started to take on a pink hue. I checked all the leads and links for continuity, and all ok. I concluded that there was insufficient metal on the prop anodes so added shaft anodes. These worked well, lasting a season, alongside all the other anodes. Never caused any vibration.
 
rafiki_ said:
My Azi had prop anodes, but these eroded rapidly and the props started to take on a pink hue. I checked all the leads and links for continuity, and all ok. I concluded that there was insufficient metal on the prop anodes so added shaft anodes. These worked well, lasting a season, alongside all the other anodes. Never caused any vibration.
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Technically, that sounds awful!!!
Think of it as an electrical circuit - you now have current flowing both ways down the shafts.
 
Hurricane said:
Technically, that sounds awful!!!
Think of it as an electrical circuit - you now have current flowing both ways down the shafts.
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There is no current flowing up or down the shaft. The current is between the two dissimilar metals and adding zinc by way of an anode will deplete rather than the zinc in the yellow metal. Nothing unusual about having both a prop nut anode and a shaft anode as the former is often small and has a short life. It will deplete first because it is the nearest to where the shaft and prop are together, then the shaft anode will deplete. This won't affect anything else in the boat.
 
Tranona said:
There is no current flowing up or down the shaft.
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I've known you for a long time but that comment seems to me to be totally incorrect.
How do you think the anodes work if there is no current flowing?
One end of the circuit is an anode (yes, thats what we call it) and the other end is a cathode (the prop/bronze).
Simply put, in an electrolyte current flows between the anodes and the cathodes.
If it doesn't there is something very wrong with physics.
 
The direction of flow of particles is irrelevant.As is the nomenclature.
The important bit is the which material (s) take which roles in the chemistry.It’s chemistry actually not Physics FWIW .
You want to end up with the expensive needy stuff like a SS shaft acting as the cathode and not deteriorating dissolving into the electrolyte the sea .
The more anodes the merrier .There is no disadvantage to extra anodes connected in .This inc shaft anodes if you wish .

Its just simple positions on the periodic table between dissimilar metals sat in electrolytes- the sea .

Those with anode protected engines have currents running all over the shop with various coolers and pencil anodes .
Different size / strength currents depending again on the difference of electro positively of the metal components of the coolers and the motors the coolers are bolted to , and the concentration of electrolytes .

As long as there’s sufficient mass of the most reactive the zinc connected in the system who cares where it is ?

Tbh it’s the critical mass that increases of zinc by placing a shaft anode ……..a good thing .

Even just dangling a old zinc in the sea off the bathing platforms in the marina helps ……does no harm .
 
When I asked a surveyor friend the question about freshwater anodes in salt water, magnesium based therefore more reactive than zinc, he did the sums for me regarding the current generated by the relevant dissimilar metals. Magnesium anodes on a bronze rudder would generate just over 2 volts of current. I cannot remember the figure for zinc but the info is available online.
Food for thought.
 
Hurricane said:
I've known you for a long time but that comment seems to me to be totally incorrect.
How do you think the anodes work if there is no current flowing?
One end of the circuit is an anode (yes, thats what we call it) and the other end is a cathode (the prop/bronze).
Simply put, in an electrolyte current flows between the anodes and the cathodes.
If it doesn't there is something very wrong with physics.
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That is correct but the current does not flow up and down the shaft as you said, but through the water between the anode and the cathode. it has no effect on any other part of the boat, so not sure why you think it is "awful" when it is doing exactly what it is intended to do. No different from using a hull anode connected to the ahaft through a wire and brushes except that the anode is closer to the item it is protecting.
 
Tranona said:
That is correct but the current does not flow up and down the shaft as you said, but through the water between the anode and the cathode. it has no effect on any other part of the boat, so not sure why you think it is "awful" when it is doing exactly what it is intended to do. No different from using a hull anode connected to the ahaft through a wire and brushes except that the anode is closer to the item it is protecting.
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So, if there isn't current flowing through the shafts, why have shaft brushes?
 
Farmer Piles said:
....Magnesium anodes on a bronze rudder would generate just over 2 volts of current.....
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Volts and current flow are two different things, think of it like Voltage is the pressure, measured in volts, and current is the flow of electrons measured in amperes. So, saying 1 amp is flowing through the circuit, is equivalent to saying ~6.24x10^18 actual electrons are flowing through it. There is a relationship of course, the greater the pressure (or voltage V) the more electrons or amps (I) will flow through for a given resistance R. V=I x R ohms law, Here we are dealing with very low voltage differences and current flows generated by the different potential differences between dissimilar metals in an electrolyte. All as clear as mud, which of course has a different potential :oops::D
 
John100156 said:
Volts and current flow are two different things, think of it like Voltage is the pressure, measured in volts, and current is the flow of electrons measured in amperes. So, saying 1 amp is flowing through the circuit, is equivalent to saying ~6.24x10^18 actual electrons are flowing through it. There is a relationship of course, the greater the pressure (or voltage V) the more electrons or amps (I) will flow through for a given resistance R. V=I x R ohms law, Here we are dealing with very low voltage differences and current flows generated by the different potential differences between dissimilar metals in an electrolyte. All as clear as mud, which of course has a different potential :oops::D
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Quite, I get the science, just an FYI really.
 
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