How many anodes?

[Chewbacka]

2 hours ago, Boater Sam said:

But I like it. And carbon tetrachloride, methylene chloride, Digoxin, and most things that are bad for me.

Don’t forget trichloroethylene in a big boiling tank.....

Edited September 6, 2019 by Chewbacka

[Boater Sam]

8 minutes ago, Chewbacka said:

Don’t forget trichloroethylene in a big boiling tank.....

Oh! Meaty stuff, used it for years, rots your boots.

[Sea Dog]

34 minutes ago, Boater Sam said:

Oh! Meaty stuff, used it for years, rots your boots.

Trichloroethylene used to dry clean sailors' suits a treat though! (I think it explains quite a lot about @mrsmelly and @Nightwatch tbh)

 

[ditchcrawler]

3 hours ago, Boater Sam said:

But I like it. And carbon tetrachloride,  

When I was in the school sailing club we use to clean the paint brushes in Carbon Tech after painting the boats up, the science lab had gallons of it, well the science master ran the sailing club.

Edit to add

This could account for lots of the rubbish I post here

Edited September 6, 2019 by ditchcrawler

[WotEver]

One place I worked at had a 45 gallon drum of the stuff in the yard and workers would just go and fill a container with however much they wanted. I was doing a fair bit of engine rebuilding at the time and I asked if I could have some for degreasing and the MD said “sure”. So I took a coffee jar to work and filled it up. The following morning the jar was empty and the plastic lid was laying all deformed at the bottom. 

[blackrose]

On 02/08/2018 at 08:22, Sea Dog said:

My point was, if the steel side in the vicinity is protected by blacking and there are no bare metal fittings close by like a prop or skin fittings, etc, what is it that the centre anodes are protecting? 

 

They're protecting the steel. Blacking doesn't last very long. Water gets under it.

 

When I've blacked my boat and left it for a year or two longer than I should. I've generally found the first signs of pitting away from the areas where the anodes are located. The areas in the vicinity of the anodes are pit-free.

On 04/08/2018 at 10:17, David Mack said:

The unpainted bottom plate?

No anodes are supposed to work on a "line of sight" basis, although I never realised they could see!

[Nightwatch]

2 hours ago, Sea Dog said:

Trichloroethylene used to dry clean sailors' suits a treat though! (I think it explains quite a lot about @mrsmelly and @Nightwatch tbh)

 

I resemble that remark!?, not to be sniffed at.

[WotEver]

16 minutes ago, blackrose said:

anodes are supposed to work on a "line of sight" basis

I’ve heard this many times although I’ve yet to read a description of the mechanism that supports the theory. Not that I’m doubting it, I’d simply like to know, if it’s true, why. 

[cuthound]

26 minutes ago, WotEver said:

I’ve heard this many times although I’ve yet to read a description of the mechanism that supports the theory. Not that I’m doubting it, I’d simply like to know, if it’s true, why. 

 

Indeed, as they work by being further down the galvanic scale thsn the metal they are protecting, you would think they would be effective in a radius of anything they were connected to, including sides and baseplate.

[WotEver]

2 minutes ago, cuthound said:

 

Indeed, as they work by being further down the galvanic scale thsn the metal they are protecting, you would think they would be effective in a radius of anything they were connected to, including sides and baseplate.

Yup

[blackrose]

14 hours ago, WotEver said:

I’ve heard this many times although I’ve yet to read a description of the mechanism that supports the theory. Not that I’m doubting it, I’d simply like to know, if it’s true, why. 

 

Yes, I'm in the same position as you so can't enlighten you any further I'm afraid. I've heard it from people who do know their stuff but I don't know how it works. It must be that weak galvanic currents in the electrolyte can only flow in straight lines between anodes and cathodes and not around corners? 

Edited September 7, 2019 by blackrose

[blackrose]

14 hours ago, cuthound said:

 

Indeed, as they work by being further down the galvanic scale thsn the metal they are protecting, you would think they would be effective in a radius of anything they were connected to, including sides and baseplate.

 

But as well as connected metal, the currents also have to flow through the electrolyte and that's the part of the galvanic circuit that can't flow (or would have more difficulty flowing) around corners.

 

Edit: Thinking about it, electromagnetic fields do flow in curves as the classical magnet/iron filing field patterns show. However, the only way the currents can flow around corners to another side of the object is to take a much longer path away from the object. My physics isn't very good, but in an electrolyte such as water wouldn't that longer path mean the already weak galvanic currents would become even weaker? The iron filings show weaker field patterns the further out they go from the magnet.

 

Perhaps this is the basis of the line of sight theory for location of anodes? If you're fitting an anode then ideally you want it in the vicinity and on the same side of the metal that you're trying to protect, especially in fresh water where galvanic currents are already very weak compared to a more efficient electrolyte such as salt water.

 

Edited September 7, 2019 by blackrose

[Chris and PJ]

On ‎07‎/‎09‎/‎2019 at 09:46, blackrose said:

 

But as well as connected metal, the currents also have to flow through the electrolyte and that's the part of the galvanic circuit that can't flow (or would have more difficulty flowing) around corners.

 

Edit: Thinking about it, electromagnetic fields do flow in curves as the classical magnet/iron filing field patterns show. However, the only way the currents can flow around corners to another side of the object is to take a much longer path away from the object. My physics isn't very good, but in an electrolyte such as water wouldn't that longer path mean the already weak galvanic currents would become even weaker? The iron filings show weaker field patterns the further out they go from the magnet.

 

Perhaps this is the basis of the line of sight theory for location of anodes? If you're fitting an anode then ideally you want it in the vicinity and on the same side of the metal that you're trying to protect, especially in fresh water where galvanic currents are already very weak compared to a more efficient electrolyte such as salt water.

 

Consider this. If you have an L shaped swimming pool and you grab the ladder that is earthed but out of the line of site of a mains unprotected hairdryer dropped into the pool are you going to receive a shock? Of course you are but its power will be diminished by the resistance of the water X the distance. Line of sight has nothing to do with it apart from extending the path.

A sacrificial anode generates a voltage when in an electrolyte and electrically connected to a more noble (cathodic)metal. The electrons from the anode flow through the cathodic metal simultaneously Ions are released into the electrolyte by the anode. In corrosion protection It is the purpose of a sacrificial anode, by sacrificing its mass by releasing ions is to generate a more negative voltage (by this loss of mass) in the cathode so that the cathode becomes less anodic and thus does not lose metal as ions into the electrolyte. In electrochemistry this is known as a redox reaction. Oxidation loses an electron while Reduction gains an electron. If mild steel loses an electron it becomes rust so it is preferred to let the sacrificial anode to effectively rust a it easy to replace.

Do not be fooled by considering canal water and especially canal marina water to be fresh water in electrochemical terms. It I something else containing the by-products (metallic salts) of years of Iron corrosion. Try drinking it if you think it is fresh water!

The ability of a magnesium anode to protect unless it is stamped with and complies with MIL-A-21412A (go google) is entirely debateable as it could be almost any  similar  looking material. In practice these voltages are measured against a silver/silver chloride half cell to prove their composition and effectiveness in any type of water (electrolyte)

A magnesium anode read -1.5v. A Zinc anode will read -1.1v. Bare Mild Steel will read -0.400. Against a Silver/ silver chloride half-cell ( the voltages for the anodes are the open circuit voltages (when not connected to the hull) Magnesium is used to account for the poor conductivity non seawater.

The achieve protection and maintain a healthy, self repairing passivation film, Bare mild steel should be between -0.7v and -0.8v The correct application of anodes achieves this there voltage reducing as current is drawn by the cathode

 

You can guess all you like but the only true way is the measure it. Go much above -0.8 volts and you will damage your paint / coatings.

I am happy to lend the necessary equipment / training to those interested.

 

 

[blackrose]

1 hour ago, Chris and PJ said:

Consider this. If you have an L shaped swimming pool and you grab the ladder that is earthed but out of the line of site of a mains unprotected hairdryer dropped into the pool are you going to receive a shock? Of course you are but its power will be diminished by the resistance of the water X the distance. Line of sight has nothing to do with it apart from extending the path.

A sacrificial anode generates a voltage when in an electrolyte and electrically connected to a more noble (cathodic)metal. The electrons from the anode flow through the cathodic metal simultaneously Ions are released into the electrolyte by the anode. In corrosion protection It is the purpose of a sacrificial anode, by sacrificing its mass by releasing ions is to generate a more negative voltage (by this loss of mass) in the cathode so that the cathode becomes less anodic and thus does not lose metal as ions into the electrolyte. In electrochemistry this is known as a redox reaction. Oxidation loses an electron while Reduction gains an electron. If mild steel loses an electron it becomes rust so it is preferred to let the sacrificial anode to effectively rust a it easy to replace.

Do not be fooled by considering canal water and especially canal marina water to be fresh water in electrochemical terms. It I something else containing the by-products (metallic salts) of years of Iron corrosion. Try drinking it if you think it is fresh water!

The ability of a magnesium anode to protect unless it is stamped with and complies with MIL-A-21412A (go google) is entirely debateable as it could be almost any  similar  looking material. In practice these voltages are measured against a silver/silver chloride half cell to prove their composition and effectiveness in any type of water (electrolyte)

A magnesium anode read -1.5v. A Zinc anode will read -1.1v. Bare Mild Steel will read -0.400. Against a Silver/ silver chloride half-cell ( the voltages for the anodes are the open circuit voltages (when not connected to the hull) Magnesium is used to account for the poor conductivity non seawater.

The achieve protection and maintain a healthy, self repairing passivation film, Bare mild steel should be between -0.7v and -0.8v The correct application of anodes achieves this there voltage reducing as current is drawn by the cathode

 

You can guess all you like but the only true way is the measure it. Go much above -0.8 volts and you will damage your paint / coatings.

I am happy to lend the necessary equipment / training to those interested.

 

 

 

I think there's one problem with your analogy: you're talking about mains currents and anodes work on the principal of very weak galvanic currents. But you obviously know more about this than me and I'm confused after your long explanation. Are you saying that line of sight has no relevance in terms of where anodes are located or not?

 

If not then I wonder why there's so much in the literature about line of sight when it comes to location of anodes?

[mrsmelly]

On 06/09/2019 at 17:31, Sea Dog said:

Trichloroethylene used to dry clean sailors' suits a treat though! (I think it explains quite a lot about @mrsmelly and @Nightwatch tbh)

 

What a lovely smell innitt ? doubt its even legal nowadays?