View Full Version : Revelations about zinc electrodes.


CDK
01-07-2011, 08:28 AM
The "inspiration" for this post are questions from local boat owners about the unexplicable rate at which zinc electrodes sometimes dissolve.
Although I believe my findings and explanations are accurate, the following is just my personal opinion. Please note that I avoid the commonly used 'zinc anode' because that is wrong. The zinc attached to the hull of a boat has a negative potential, so it should be called a cathode: steel structures on land are also protected by negative electrodes, a system called cathodic protection.

1. It is a widespread believe that zinc electrodes must loose their mass over time and that an electrode behaving differently is not properly installed.
This is not the case! A zinc electrode is only sacrificed if it is electrically connected to a metal hull that suffers from paint flaws or damages, or purposefully exposed metal areas. A metal hull with a good paint layer will provide no electrical path, so the zinc electrodes will be inactive.
For a zinc electrode to become active, a closed circuit must be present.

In the left hand picture you see two pieces of steel tube that I cleaned and hung in a bucket of seawater. One had an electrode attached to it, in this case a sliver of aluminum, the other one had none.
Before the test I measured the current between the electrode and the steel and also the open voltage potential. The current was slightly more than 30 milli-amps, the open voltage approx. 600 milli-volts.
Both objects remained immersed for 5 days.

2. External influences.
The piece with the electrode attached came out almost as clean as I put it in, so the electrode does protect exposed steel. But the other piece was covered in light brown iron oxide. The coating was much thicker than expected, as much as 10 times the rust that is formed if a piece of steel is submerged for 5 days.
The reason for this fierce attack can only be that the electrolysis near the sacrificial electrode (it was actually foaming) ionized some H2O and NaCl, making it much more aggressive even for steel in the vicinity without any electrical connection but the water it is in.

The lesson is twofold.
A metal boat in the berth next to yours having damaged underwater paintwork may cause damage to your hull as well or at least activate your zinc electrodes causing them to dissolve quickly.
And a shore power cable with the ground wire attached to your hull can play havoc to your electrodes if other hulls are grounded in a similar way or if the shore is lined with steel plates.

3. Faulty electrode construction.
The center picture show a very common zinc electrode at the bottom with a cast in galvanized steel strip.
If attached with stainless or brass fasteners, the electrode will protect these fasteners. But the zinc around the steel strip is very thin, so will quickly disappear and then the electrode will protect its own part until all the zinc has gone. During the process there is a current loop between the zinc and the very nearby steel, so the electrode is no longer effective against a paint scratch further away.

The electrode in the picture weighs 2 lbs and costs $20 to $40 depending on where you buy it.
The market price (LME) for zinc is approx. $1 per lb....
In the upper half you see my solution: a simple piece of zinc with a weight of almost 3 lbs, cut from a 36 lbs strip I bought for $27. The drawing shows how to attach this $2.25 electrode.

It is of paramount importance to cover the nut and surrounding area with an insulating coating. I used 3M industrial sealant nr #800 but you can also use Sikaflex or a marine paint. Instead of an O-ring under the electrode a small piece of rubber hose could also be used. Even if it isn't 100% waterproof, the lack of motion within the seal will minimize chemical activity.

4. Shaft electrodes.
These will wear much less if the shaft and prop are painted. I've seen lots of shafts in our wintertime marina, 8 out of 10 were bare metal, causing the expensive shaft electrodes to work overtime.
Some were almost like new, so probably not electrically connected to the shaft, in one case I could easily rotate the electrode with one hand....

anthony goodson
01-07-2011, 08:59 AM
Thankyou for that CDK ,what material are the fastenings in your diagram ,and what are the parameters that lead you to that choice ?

gonzo
01-07-2011, 09:02 AM
I find that stray current is the main culprit of excessive wear on the "anodes". Many boats have horrible electrical installations and older marinas are not any better.

michael pierzga
01-07-2011, 09:23 AM
What alloy are your Zinc anodes ?

gonzo
01-07-2011, 09:40 AM
Zinc anodes are not considered an alloy. They should be over 99% pure.

michael pierzga
01-07-2011, 10:13 AM
Wrong...Marine zinc anodes are always a zinc alloy... MilSpecA-18001K. Pure zinc passivates. A passivated anode surface is no longer active...your zincs will last forever.

Marine zinc anodes contain Aluminum and Cadmium to promote erosion of the surface and keep fresh zinc available. Do not use bulk zinc underwater and always use anodes with embedded steel plates to generate a perfect electrical bond between the zinc alloy and the bonding strap, plate, hull. Always fasten with fan disc washers to promote a secure electrical connection .

When in doubt consult the technical documents.

http://www.mgduff.co.uk/leisure-craft/fitting-instructions/aluminium.html

viking north
01-07-2011, 10:21 AM
Gonzo, i think you hit the nail on the head, re stray currents.On my first conversion, an aluminium hull, I was given advise by an fellow alum. hull owner, when visiting marinas or where in a crowded anchorage to drop a big zinc over the side hanging off a #8 or so wire electrically connected to the hull. Seemed to work for him as his home port was a marina and his big zincs were being eaten.

WickedGood
01-07-2011, 10:46 AM
What do you think of using conductive grease betwwen the Zinc and Drive Shaft?

what about using the same grease on the Bronze/Nibil Prop to a stainless shaft?


You reccomend painting the shaft & Prop?
Would a copper based antifouling or Tin Base be better on a fiberglass boat that is bottom painted with copper.

CDK
01-07-2011, 11:35 AM
Thankyou for that CDK ,what material are the fastenings in your diagram ,and what are the parameters that lead you to that choice ?

As long as you provide good electrical contact with the parts you want to protect and insulate the contact area against water, it doesn't matter what you use. I took stainless bolt and nuts because they can be removed without much effort even after years.

On my own boat I use zinc to protect just the stainless objects like shafts, stern tubes and rudders. The questions put to me were from sailing yacht owners, where a grp hull is combined with an iron keel.

CDK
01-07-2011, 11:48 AM
What do you think of using conductive grease betwwen the Zinc and Drive Shaft?

what about using the same grease on the Bronze/Nibil Prop to a stainless shaft?


You reccomend painting the shaft & Prop?
Would a copper based antifouling or Tin Base be better on a fiberglass boat that is bottom painted with copper.

I don't think there is a conductive grease for this task.
But good quality shaft electrodes have two small pieces of copper protruding from the inner surface. Secured to a clean shaft they provide an immaculate electric contact. You could apply a smear of Molykote copper grease, not to provide contact but to fill the gap and keep the water out.

If you paint the shaft and prop, you prolong the life of the zinc. But I know that paint on a prop won't stay there long.

CDK
01-07-2011, 12:01 PM
Zinc anodes are not considered an alloy. They should be over 99% pure.

That's about right Gonzo. We are talking about industrial zinc here, used for protection of steel by hot dipping or galvanizing. It still is contaminated with other elements from the ore, but not enough to call it an alloy.

For use in electrodes alloys are also used, but I would prefer pure metals because the properties are better known. For complex shaped electrodes on outboards or stern drives sometimes an alu/zinc alloy called Zamac is used because it flows better in the mold.

gonzo
01-07-2011, 12:32 PM
I have never heard of zinc "passivating". In plating operations the zinc has less than .5% impurities and keeps on flowing to whatever is being plated.

michael pierzga
01-07-2011, 12:52 PM
Reducing exposed metal reduces anode wear. Prop and Shaft anodes are subject to cavitation erosion and wear fast. Good shaft anodes have embedded copper conductors on the inside...shaft contact surface, for superior electrical contact. Normally all that is needed is to clean the shaft for good electrical contact and torque on. Be sure that your shaft is electrically bonded to the hull.

They say tin based antifoul preserves anodes. I cant see the difference. On big yacts in the Med you moor stern too. The docks are made of steel covered in concrete. Aft facing rudder anodes erode fast. Not much you can do...that is why they are fitted. Not sure what zinc anode challenges you have in Maine.

When anode dont erode...you have a problem.

michael pierzga
01-07-2011, 01:01 PM
I have never heard of zinc "passivating". In plating operations the zinc has less than .5% impurities and keeps on flowing to whatever is being plated.


Err emmm, read. Youre a marine surveyor......The Internet is a good source of knowledge. Thousands of documents concerning passivisation .

http://www.boatzincs.com/use_milspec_a18001k.html

gonzo
01-07-2011, 01:10 PM
The link confirms what I said. Less than .5% impurities. MIL SPEC .005% iron

michael pierzga
01-07-2011, 01:32 PM
Read carefully...very carefully. PASSIVATION is a new term for you. And it is not clear exactly what you said.

Iron is a manufacturing contaminate. Great lengths are gone to avoid this iron contamination to achieve milspec anode class. . The molten zinc is handled with graphite ladles and in graphite molds. The mil spec anode alloy contains added alum and cadmium.

MilSpec Marine anodes are precision manufactured , not simply lumps of zinc.

gonzo
01-07-2011, 01:46 PM
This is what you wrote:

Wrong...Marine zinc anodes are always a zinc alloy... MilSpecA-18001K. Pure zinc passivates. A passivated anode surface is no longer active...your zincs will last forever.

Marine zinc anodes contain Aluminum and Cadmium to promote erosion of the surface and keep fresh zinc available. Do not use bulk zinc underwater and always use anodes with embedded steel plates to generate a perfect electrical bond between the zinc alloy and the bonding strap, plate, hull. Always fasten with fan disc washers to promote a secure electrical connection .

When in doubt consult the technical documents.

http://www.mgduff.co.uk/leisure-craft/fitting-instructions/aluminium.html

Now you contradict yourself and say that they are not alloys but pure. This post is typical of yours. When you are found to be wrong, you change position and engage on personal attacks. Grow up boy.

cthippo
01-07-2011, 03:12 PM
They discovered that by alloying the zinc with small amounts of the elements aluminum and cadmium, an increased amount of iron could be tolerated. So, the sacrificial anode specification was changed to allow an increase in the iron content to 0.005 percent.

From here:

http://www.boatzincs.com/use_milspec_a18001k.html

gonzo
01-07-2011, 03:37 PM
That is correct, it can have more impurities than originally thought. However, the key word is "tolerated".

cthippo
01-07-2011, 06:22 PM
That is correct, it can have more impurities than originally thought. However, the key word is "tolerated".

The Al and Cd are intentionally added though, so it is indeed an engineered ally. The Fe is a tolerated contaminant.

gonzo
01-07-2011, 06:55 PM
Depending on the installation, iron deposits may or not be a problem. Some need aluminum or magnesium instead of zinc. For example, outdrives and outboards. Also, the salinity of the water has a lot of importance in the choice.

CDK
01-08-2011, 04:16 AM
This is what you wrote:



Now you contradict yourself and say that they are not alloys but pure. This post is typical of yours. When you are found to be wrong, you change position and engage on personal attacks. Grow up boy.

I think the keyword here is histrionics.

This whole discussion about Mil spec doesn't make sense to me. The idea behind Mil specs is a bureaucratic instrument to ensure the army gets the best the industry has to offer. Which of course they don't, they only pay more.

Zinc simply is a very cheap metal, suitable for only two applications: to protect iron and steel and be sacrificed doing that, or serve as the negative electrode in a primary cell, where it is also eaten by the electrolyte.

anthony goodson
01-08-2011, 06:10 AM
Thankyou again for your reply CDK ,the reason I asked the question was that many years ago I was told by a person who's knowledge I respected that the correct way to protect aluminium ,LM25 in this case ,in seawater was to use mild steel fittings to the anodes. I never asked why ,and I will admit it didn't make sense at the time.Your reasoning for using stainless is logical and does make sense. Since I only use GRP jets in GRP hulls now the question to me is academic, but it is something I have wondered about.

michael pierzga
01-08-2011, 08:53 AM
You indeed use mild steel with aluminium underwater...the galvanic scale indicates that Aluminium and mild steel are most compatible.
...
magnesium,
zinc,
aluminum,
mild steel,
cast iron,
stainless steel (type 410, active),
lead,
Monel,
Muntzmetal,
manganese bronze,
naval brass, yellow brass,
aluminum bronze,
copper,
silicon bronze,
nickel,
stainless steel (types 304, 316, and 410, passive).

viking north
01-08-2011, 09:04 AM
Good article, again zincs, like all metals today, the importance of purchasing from a reputiable manufacturer is so important, content is simply something printed on a label. A topic i stressed on another thread regarding stainless. In this part of the world i am a fanatic about where my marine products are manufactured and don't mind paying a little more for a good product. Two important points made in this thread,#1 good electrical bonding of the zinc. #2 zincs are sacrifical and after a normal sailing season,(5 to 6 m),should show some signs of being eaten away, if not recheck your bonding to be sure. If completely dissolved before that time suspect unwanted electrical activity either with your own vessel (not good but something you have a degree of control over) or stray activity in the area you keep you boat for long periods of time (something you most likely don't have much control over, so haul out mid season and replace your zincs. As a former owner of an aluminium hull on it's first season afloat,i was a fanatic about checking the zincs, donning fins and mask once a month. Speaking of stray electrical activity, there a big debate by wooden boat owners regarding weather or not to bond thru hulls. Good topic, maybe this little teaser will keep it going into the field of zincs and hull materials and proper electrical practices within ones own craft. Geo

gonzo
01-08-2011, 10:04 AM
Outboards and outdrives have stainless bolts on their factory install anodes. They perform well. Carbon steel will corrode and be almost impossible to remove.

michael pierzga
01-08-2011, 10:56 AM
Outboards are cast alloy and are closer to ss on the scale. Refer to the above metals table for Al Si Bronze alloys
Outboard casting are A367.0 or A368.0 AlSi alloy .

gonzo
01-08-2011, 11:04 AM
I can't think of anything on a boat, except maybe a frying pan, that would not be an alloy and just plain aluminum.

viking north
01-08-2011, 11:22 AM
I can think of an example thats not an alloy, the whole boat it's 99.9999%gold, and in many cases fools gold or at least it's weight in gold to produce it. My frying pan is cast iron, useful in repelling borders but the downside is when it's in the hands of an iriate wife.

gonzo
01-08-2011, 11:24 AM
304 is not higher than nickel and monel. That list is wrong.

michael pierzga
01-08-2011, 11:26 AM
All yachts are made of "fools gold".... Praise the Lord ! ...gold platted yachts are how I make my living..

viking north
01-08-2011, 02:23 PM
Gonzo is correct,For a detail galvanic scale see post #217 under Reverse Engineering (conversions /modifications)

viking north
01-08-2011, 02:30 PM
And may it continue Michael, to maintain a democracy always question authority vigoursly, to maintain capitalism is is the duty of those that need take (earn it) from those that have , much like the galvanic scale. mucho, mucho where possible, Geo.

MikeJohns
01-09-2011, 06:21 AM
Cornelius

I think they are correctly called Anodes

If you consider the cell as a box filled with electrolyte with two immersed electrodes, one being the Zinc and the other steel (a bare patch of protected steel). The Hull of the boat is then the external circuit. Within the electrolyte just consider which way the cations flow. That more properly defines the electrochemical cell.

As for self corrosion, protective zincs are alloyed to produce a surface which sheds its oxidised material.
Just how the zinc responds will depend on salinity and temperature. Self 'cleaning' anodes are considered mandatory.
Pure zinc can become considerably less effective and I've seen blocks of pure zinc with a crust that insulated it very effectively, in fact i could get no connection anywhere on the surface of the zinc. An alloyed sacrificial zinc never does this.

Of course Just how the zinc responds will depend on salinity and temperature.

Self 'cleaning' anodes ( alloyed) are considered mandatory and are incorporated into standards. the Milspec anode composition standard is just one such standard.

I'd rather see steel straps cast into the anode and steel studs on a steel hull.
I always specify that anode straps, mounting hardware and even the backs of the anodes be epoxied or sealed and I like to see the sides of the anodes painted too so the only bare face is away from the hull. This solves a lot of paint blistering problems around the anodes.

If the boat is left and the anode material completely erodes you don't want more noble material around like SS anode straps.

And we paint bronze props very effectively with epoxy and hard antifouling. Unless the prop cavitates the paint is often immaculate, it certainly isolates a large amount of very noble material. We have fishing boats that have been doing this for 15 years with no shaft anode ( although they do have a grease filled shaft and the shaft is also epoxied up to the bearing).

Zincs are often problematic and will sometimes damage paint even stripping it. Ironically overprotection can lead to extensive coating failure followed by very quick anode depletion and then severe corrosion. Often boats labelled 'problem boats' would actually be better with no anodes at all.

I posted something on over protection here:

http://www.boatdesign.net/forums/materials/blisters-around-zincs-steel-boat-23941.html#post225055

CDK
01-09-2011, 07:05 AM
Mike, except for the anode bit I fully concur. You clearly have studied the topic well.

Isolating the straps is a good remedy to keep these expensive electrodes from sacrificing themselves by protecting their own straps. But you are an exception, I didn't find one boat in the marina where someone took the trouble to paint the straps, shafts or props.

The anode/cathode confusion may well originate from the times electricity was supposed to flow from + to -, but now we know better. Even Wikipedia has confusing texts about it.
Such differences are inevitable. I watch a TV program about your border control where they always talk about revoking "a visa". But visa is the plural form of visum, a word that is immediately red underscored by the Windows spell checker.

Ad Hoc
01-09-2011, 07:55 AM
Interesting debate. As for the anode or not to anode…this is my take:

Immersing 2 different metals into an electrolyte solution, such as sea water, a current flows from the anodic, or base metal, to the cathodic, or noble metal. The noble metal tends to be protected, and hence the anodic or base is the metal that is depleted.

Thus looking at the galvanic chart Zinc is the lowest down at a nominal -1130mV, with aluminium around -760mV and carbon steels around -610mV.

To protect the ally or steel, using zinc, this is an anodic reaction from the zinc to the noble metal or ally/steel, the zinc experiencing corrosion whereas the noble metal is protected. Hence using zinc is termed an “anode”. I’m with Mike on this.

Mind you, also worth noting when discussing aluminium there are anodic and cathodic polarization reactions that can take place on the surface of aluminium. As Mike noted, owing to the differing composition of electrolyte solutions because the behaviour of the Al-ions is related to the chemistry of the aluminium in the electrolyte. Since it is possible that in the presence of a crack/pit, aluminium can repassivate under the right conditions; anodic film formation.

Joakim
01-09-2011, 08:06 AM
What about saildrives and bronze folding propellers? I have a Yanmar SD20 with Volvo-Penta two blade bronze folding (likely the same as Radice and Allpa). Both the SD and the propeller have zinc anodes. The propeller is not painted. The propeller zincs wear quite rapidly lasting only 1-2 seasons despite the conditions around here (cold water, salinity ~0.5%, 5 kk season). The saildrive zincs seems to last 3-4 seasons and outboard zincs seem to last forever.

Does a bronze propeller even need the zincs? Not all brands have them. Looking at the rare painted propellers paint doesn't seem to last well. Should I paint? What paint should be used?

michael pierzga
01-09-2011, 08:24 AM
Gonzo is correct,For a detail galvanic scale see post #217 under Reverse Engineering (conversions /modifications)

What is Gonzo correct on ?

viking north
01-09-2011, 08:34 AM
CDK, re electricity flowing from + to - this is known as field as in E(electric field flow) and flowing from - to + is known as electron as in I (current flow). Both are correct as both make up electrical power ExI=Watts. In modern electrical/electronic theory both are intermingled, however the tendancy today is to use electron flow to follow the operation of electrical/electronic circuits and field flow for the operation of capacator,transformer and antenna theory. Geo. CET.

viking north
01-09-2011, 08:48 AM
Michael, on the standard listing of the galvanic scale, see my post #32 reference, unless i'm missing a point you were trying to make by your order of listing, If so I stand corrected. Powerful statement "I stand corrected" It's a no lose situation, IE maintainds civility without eating crow,(smiley face ) Geo.

CDK
01-09-2011, 09:06 AM
Interesting debate. As for the anode or not to anode…this is my take:

Immersing 2 different metals into an electrolyte solution, such as sea water, a current flows from the anodic, or base metal, to the cathodic, or noble metal. The noble metal tends to be protected, and hence the anodic or base is the metal that is depleted.

Thus looking at the galvanic chart Zinc is the lowest down at a nominal -1130mV, with aluminium around -760mV and carbon steels around -610mV.

To protect the ally or steel, using zinc, this is an anodic reaction from the zinc to the noble metal or ally/steel, the zinc experiencing corrosion whereas the noble metal is protected. Hence using zinc is termed an “anode”. I’m with Mike on this.

Mind you, also worth noting when discussing aluminium there are anodic and cathodic polarization reactions that can take place on the surface of aluminium. As Mike noted, owing to the differing composition of electrolyte solutions because the behaviour of the Al-ions is related to the chemistry of the aluminium in the electrolyte. Since it is possible that in the presence of a crack/pit, aluminium can repassivate under the right conditions; anodic film formation.

So you're another adversary John, I can live with that:D.

The zinc has the lowest potential, so the current flows from the zinc to the hull (where exposed). Because my background is electronics, the negative side, where the electrons are coming from, must be the cathode.
That goes for the now extinct electron tubes, diodes, thyristors etc. A CRT used to be a cathode ray tube, the anode is the screen, being the receiving end
Also the carbon pile in a primary cell is the anode, because it is positive, the zinc can is a cathode.

But it remains difficult. There is a lot of anodized aluminum on this planet, not suitable for cathodes nor anodes....

CDK
01-09-2011, 09:17 AM
What about saildrives and bronze folding propellers? I have a Yanmar SD20 with Volvo-Penta two blade bronze folding (likely the same as Radice and Allpa). Both the SD and the propeller have zinc anodes. The propeller is not painted. The propeller zincs wear quite rapidly lasting only 1-2 seasons despite the conditions around here (cold water, salinity ~0.5%, 5 kk season). The saildrive zincs seems to last 3-4 seasons and outboard zincs seem to last forever.

Does a bronze propeller even need the zincs? Not all brands have them. Looking at the rare painted propellers paint doesn't seem to last well. Should I paint? What paint should be used?

The zinc bolted to the prop nut has the harsh life of a midget protecting a giant. I have Allpa shafts with bronze props: in the Adriatic sea the zinc electrodes are completely gone within 3 months.
I tried to paint the props with expensive Volvo stuff, but that was a waste of money. Will try epoxy this season.

michael pierzga
01-09-2011, 10:26 AM
Michael, on the standard listing of the galvanic scale, see my post #32 reference, unless i'm missing a point you were trying to make by your order of listing, If so I stand corrected. Powerful statement "I stand corrected" It's a no lose situation, IE maintainds civility without eating crow,(smiley face ) Geo.


Well Viking North, if you or CDK or Gonzo would like to re write the galvanic table then you must supply a link to prove of your observations and educate us readers.

This is the link I abide by

http://www.mcnallyinstitute.com/04-html/4-1.html

So far I have not seen any new knowledge, nor observations in this thread.

CDK is still not sure why anodes on props and shafts wear faster ...the literature concerning cavitation erosion of anodes on props and shafts is widely available.

Questions are being posed about the compatibility of SS and aluminium. Please supply the relevant links to prove your observations..



CDK appears to be not aware that Zinc anodes are an alloy...the literature on zinc "passivisation" and the proper alloy composition of
zinc anodes are widely available.

CDK appears to believe that steel inserts moulded into zinc anodes promote erosion...supply the relevant literature that proves this theory.

BertKu
01-09-2011, 10:47 AM
Because my background is electronics, the negative side, where the electrons are coming from, must be the cathode.
That goes for the now extinct electron tubes, diodes, thyristors etc. A CRT used to be a cathode ray tube, the anode is the screen, being the receiving end
Also the carbon pile in a primary cell is the anode, because it is positive, the zinc can is a cathode.

....

CDK, I am fully in agreement with you. Only electronic people will confirm that the zinc is the cathode. It is logical, as the electrons are taken away from the zinc to the more noble metal. for that reason the noble metal does not deteriorate. All non electronic people will still believe that the current flows from the plus to the minus.
Bert

michael pierzga
01-09-2011, 10:50 AM
Anode Cathode marine corrosion table


GALVANIC SERIES OF METALS AND ALLOYS .....


CORRODED END ( ANODIC OR LEAST NOBLE)

MAGNESIUM
MAGNESIUM ALLOYS
ZINC
ALUMINUM 5052, 3004, 3003, 1100, 6053
CADMIUM
ALUMINUM 2117, 2017, 2024
MILD STEEL (1018), WROUGHT IRON
CAST IRON, LOW ALLOY HIGH STRENGTH STEEL
CHROME IRON (ACTIVE)
STAINLESS STEEL, 430 SERIES (ACTIVE)
302, 303, 304, 321, 347, 410,416, STAINLESS STEEL (ACTIVE)
NI - RESIST
316, 317, STAINLESS STEEL (ACTIVE)
CARPENTER 20CB-3 STAINLESS (ACTIVE)
ALUMINUM BRONZE (CA 687)
HASTELLOY C (ACTIVE) INCONEL 625 (ACTIVE) TITANIUM (ACTIVE)
LEAD-TIN SOLDERS
LEAD
TIN
INCONEL 600 (ACTIVE)
NICKEL (ACTIVE)
60 NI-15 CR (ACTIVE)
80 NI-20 CR (ACTIVE)
HASTELLOY B (ACTIVE)
BRASSES
COPPER (CA102)
MANGANESE BRONZE (CA 675), TIN BRONZE (CA903, 905)
SILICONE BRONZE
NICKEL SILVER
COPPER - NICKEL ALLOY 90-10
COPPER - NICKEL ALLOY 80-20
430 STAINLESS STEEL
NICKEL, ALUMINUM, BRONZE (CA 630, 632)
MONEL 400, K500
SILVER SOLDER
NICKEL (PASSIVE)
60 NI- 15 CR (PASSIVE)
INCONEL 600 (PASSIVE)
80 NI- 20 CR (PASSIVE)
CHROME IRON (PASSIVE)
302, 303, 304, 321, 347, STAINLESS STEEL (PASSIVE)
316, 317, STAINLESS STEEL (PASSIVE)
CARPENTER 20 CB-3 STAINLESS (PASSIVE), INCOLOY 825
NICKEL - MOLYBDEUM - CHROMIUM - IRON ALLOY (PASSIVE)
SILVER
TITANIUM (PASS.) HASTELLOY C & C276 (PASSIVE), INCONEL 625(PASS.)
GRAPHITE
ZIRCONIUM
GOLD
PLATINUM



PROTECTED END (CATHODIC OR MOST NOBLE)

BertKu
01-09-2011, 11:02 AM
Anode Cathode marine corrosion table


GALVANIC SERIES OF METALS AND ALLOYS .....


CORRODED END ( ANODIC OR LEAST NOBLE)

PROTECTED END (CATHODIC OR MOST NOBLE)

O.K. thus those engineers of this website believe that the extra electrons, which get added to the zinc material forms the corrosion.( if the zinc is the anode, because any electronic person will confirm that electrons will flow from lower potential to higher potential) Now we have a new theory contradicting Einstein.
Bert

gonzo
01-09-2011, 11:29 AM
Michael: Which of the lists you claim is correct? You posted two with metals in different order.

viking north
01-09-2011, 11:46 AM
The way it see it and it conforms with basic electrical theory which we all studied prior to advancing onto electronics, technicions, technologists, and finally engineer is electrons are looked upon as particles(part of) and flow from the more neg(least pos.) or cathode acting to the least neg.(more pos.) anode acting(plate, collector,). Thus the cathode or zinc becomes depleted much in the same way old vacuum tubes cathodes became weak emitting over time. Thats my story and i'm sticking to it, and now i have to put the snow tires on the car, as we are having our first snow here in Halifax, Nova Scotia, Certified Electronic Engineering Technicion, Geo.

gonzo
01-09-2011, 11:48 AM
It is important to remember that the positive pole on an electrical circuit has a negative charge. That is where the charge(electrons) are accumulated.

viking north
01-09-2011, 12:10 PM
Gonzo, welcome to my world, this time i have to say you are wrong, The key word here is as you have used,"circuit" no electrons gather at the positive pole as it is part of a closed circuit othewise no electron flow takes place. The pos. pole, (anode, plate, collector is just a physical location for the sake of convenience to explain a circuits operation. From this pos. pole(anode,plate,collector) the electrons do not really accumilate but are merely attraced and from there move on thru the circuit back to their source. Geo.

BertKu
01-09-2011, 02:45 PM
Gonzo, welcome to my world, this time i have to say you are wrong, The key word here is as you have used,"circuit" no electrons gather at the positive pole as it is part of a closed circuit othewise no electron flow takes place. The pos. pole, (anode, plate, collector is just a physical location for the sake of convenience to explain a circuits operation. From this pos. pole(anode,plate,collector) the electrons do not really accumilate but are merely attraced and from there move on thru the circuit back to their source. Geo.

Folks, we all have a car, or most of us. We all have wondered why the plus of the battery got sometimes that white substance. You see, you see, Bert you are wrong. It is the plus which is oxidizing, therefore the anode must be the zinc. Sorry guys, wrong. You forgot that the voltage regulator is 14,4 Volt and therefore the plus pole of the battery becomes negative towards the higher regulator voltage. Hereby given the proof, that the zinc has to be the cathode and cannot be the anode. (sorry to illustrate it in a simple form, whereby we all can visualize the reasoning)

Bert

CDK
01-09-2011, 03:08 PM
All non electronic people will still believe that the current flows from the plus to the minus.
Bert

There is even a poster here who still believed the world was flat, but with help from Google and cut&paste he is an expert in every field now.

viking north
01-09-2011, 03:30 PM
Ok enought of this babble, First we have to determine if the zinc is acting as a battery with salt water as the electrolite and apparently the concensis is that is the case. So now we have to get into the internal operational theory of a battery which involves another factor the chemical reaction. The other discussion that is happening here is the external operation of circuits, external to the battery where there is no chemical action involved thus a slightly different take on what occurs. Two more factors play a role, are we working with AC or DC. In the case of zincs depleting we could be working with one or both within the hull or with the external stray electrical energy. It is not as simple as it seems as believe it or not the zinc hull external circuit could actually be rectify the AC into pulsating DC(solid state theory). So maybe we're all right, the important thing is Zincs seem to work as long as they deplete. Be interesting to play around with studying if they are as equally effictive against AC, DC or Pulsating DC. Just kidding, Geo.

gonzo
01-09-2011, 03:57 PM
Flow, according to electric theory, can be calculated in two ways. The electrons flow from the positive to the negative, or holes flow from the negative to the positive. The only difference is on a plus or minus sign in the formula.
Viking, yes you are correct, the electrons are not accumulated at the pole. It was not the most technically correct statement ;)

MikeJohns
01-09-2011, 06:28 PM
Cornelius et al

Confusion about Anode and Cathode abound. Sometimes it's not obviously apparent which is which depending on your frame of reference and your adopted definition.

In an electrochemical cell, such as a galvanic cell in seawater, the electrodes are defined by the reactions that occur at the electrode.

I said before the key is to consider where the Cations are reduced. This is by definition the Cathode, the oxidation reaction is always at the anode.

People from all walks of life get very confused and hung up on misleading definitions of Anode and Cathode, particularly the Electrical fraternity ;).

Consider a rechargeable battery and try and define the electrodes in terms of current flow !
Consider an electronic component and try and define its leads in terms of polarity across the device ! What I'm trying to say is that one simple definition doesn't hold. There are convenient frames of adopted reference but they are not definitive.

However it is definitive that in an electrochemical cell you consider the oxidation and reduction reactions to define your Anode and Cathode.

This even works with the rechargeable battery, Anions are oxidised at the Anode when anions are being produced and Cations are reduced at the cathode when cations are being produced.

As we saw above all of this is made even more confusing by the adopted convention of the electrical fraternity that talk of current as the movement of holes (which they understand implicitly) but contrary to the actual movement of electrons.

So Cornelius is arguing from an adopted Electrical perspective but he's falling into a common trap. IMHO

gonzo
01-09-2011, 07:00 PM
The hole thing takes some effort to get your head around.

Ad Hoc
01-09-2011, 07:59 PM
The hole thing takes some effort to get your head around.

Sure does...ive read loads of books on this, none 100% clear..but all saying roughly the same thing.

But, to confuse matters further, corrosion is correctly interpreted by the pH of the solution. Since what is going on was first discovered by Nerst, when he found that copper in copper sulphate solution becomes positive whilst zinc in zinc sulphate solution becomes negative. The Nerst equation basically represents the corrosion behaviour of metals in aqueous solutions in terms of pH and the potential E and thus leading to the formation of the Pourbaix diagrams. And if that wasn’t enough, these diagrams only provide information on reactions that can occur, not necessarily on reactions that will occur. Which then leads back to polarization and overvoltage and gives us the relationship between the current and the electrode potential. The degree of polarisation is a measure of how the rates of the anodic and the cathodic reactions are retarded by various environmental and/or surface process factors.

BertKu
01-10-2011, 03:01 AM
The hole thing takes some effort to get your head around.

This is vry much true.

Can I add some more confusion to this issue, by stating, that I have charged some hunderds of SLABs and was very puzzled why the negative terminal of the battery often got oxidized with white powder and not the plus terminal. I could only conclude that it has to do with the crocodile clips (different material) , together with the salt in the air (close to the coast) My conclusion is that one has to be damn carefull what kind of bolts to use when mounting the zinc. I am not buying AC, Viking North, otherwise both, also the noble material maybe oxidised. The hole theory is another story. When the electrons are removed of the outer ring, yes a hole exsist, but the hole is not moving. The electrons does.
Bert

Wynand N
01-10-2011, 03:43 AM
Interesting debate. As for the anode or not to anode…this is my take:

Immersing 2 different metals into an electrolyte solution, such as sea water, a current flows from the anodic, or base metal, to the cathodic, or noble metal. The noble metal tends to be protected, and hence the anodic or base is the metal that is depleted.

Thus looking at the galvanic chart Zinc is the lowest down at a nominal -1130mV, with aluminium around -760mV and carbon steels around -610mV.

To protect the ally or steel, using zinc, this is an anodic reaction from the zinc to the noble metal or ally/steel, the zinc experiencing corrosion whereas the noble metal is protected. Hence using zinc is termed an “anode”. I’m with Mike on this.

Mind you, also worth noting when discussing aluminium there are anodic and cathodic polarization reactions that can take place on the surface of aluminium. As Mike noted, owing to the differing composition of electrolyte solutions because the behaviour of the Al-ions is related to the chemistry of the aluminium in the electrolyte. Since it is possible that in the presence of a crack/pit, aluminium can repassivate under the right conditions; anodic film formation.

I just have to chime in and will then slide back into the obscurity of retirement;)

To keep busy Im running a small electroplating business from home and do electro zink, nickle, tin, copper, chrome and gold plating and of course aluminum oxidizing - plain, colors et all.

The principle of electrolysis is used for plating where an anode (positively charged) and a cathode (negatively charged) is placed in an electrolyte (in boating world, sea water).
Positive ions flow from the anode toward the object being plated (cathode), through the plating solution (the electrolyte), and
are deposited onto the surface of the object. The longer the system is left on, the thicker the resulting plating will be.
Regardless of the size of object plated the voltage used is only 3 - 5VDC max (sometimes less with copper plating) although current is adjusted as needed.

IOW, not a lot of electric flow is needed to start the electrolysis process and the nearer the cathode is to the anode, the higher the current drawn is gonna be. (same principle as old liquid controller rheostats).
So it makes sense to place anodes as close as possible to the more noble material such as the SS prop shaft, brass propeller etc to be efficient. That said, the positively charged zink ions of the sacrificial anode did not disappeared in the seawater, but is deposited on the nearest cathode say for instance the brass prop...


As AdHoc pointed out, aluminum should be mentioned as well.

Anodising is an electrochemical process that thickens and toughens the naturally occurring protective oxide layer in aluminium (on surface). The
resulting finish, depending on the process, is the second hardest substance known to man, second only to the diamond. The anodic coating is part of the metal, but has a porous structure that allows secondary infusions (organic and inorganic coloring, etc.)

Basically the process is reversed from the "normal" electrolysis process whereas the aluminum to be anodized become the anode (positive) and a negative charged electrode is put in the electrolyte and the current releases hydrogen at negatively charged electrode and oxygen forms on the surface of the positively charged aluminum (anode) creating a buildup of aluminum oxide - basically speeding up the natural oxidizing process that makes ally durable and controlling the thickness thereof.
Although different electrolytes are used, the most common is a water and sulfuric acid mix and the voltage used much higher than normal electrolysis at about 19VDC.

BertKu
01-10-2011, 04:31 AM
You know guys, this story reminds me to the new vacuum cleaner I bought some time ago. Until my wife asked me. Please may I have the HOOVER" What hoover I never bought a hoover , I bought a cheap China one.

But it is so ingraved in peoples mind, that we still call a vacuum cleaner a hoover.

So again, we still call the zinc anodic, while actual it is the cathode.
Bert

rwatson
01-10-2011, 05:59 AM
You know guys, this story reminds me to the new vacuum cleaner I bought some time ago. Until my wife asked me. Please may I have the HOOVER" What hoover I never bought a hoover , I bought a cheap China one.

But it is so ingraved in peoples mind, that we still call a vacuum cleaner a hoover.

So again, we still call the zinc anodic, while actual it is the cathode.
Bert

Thanks for the mental exercise guys - its always fun to retrace basic concepts and refresh minds.

The best explanation of the +ve, -ve concept that trips people up that I have come across, is the link
http://www.allaboutcircuits.com/vol_1/chpt_1/7.html

where Benjamin Franklin screws up current flow concept.

So now we have "Conventional" flow notation, where the current is designated as travelling from the Positive to the Negative side. Its not true, but it still works for circuit design and calculation.

In reality though, in "Electron flow notation", the electrons travel from Negative to Positive.

Then, I got onto the defintion of a Cathode , at good old peer reviewed Wikipedia.
http://en.wikipedia.org/wiki/Cathode

The quote "A widespread misconception is that cathode polarity is always negative.. In fact cathode polarity depends on the device type, and can even vary according to the operating mode"

If you look up the definition of Anode, of course it says "A widespread misconception is that Anode polarity is always positive (+). "

So, how is Cathodic protection working ?
http://en.wikipedia.org/wiki/Cathodic_protection

"Cathodic protection (CP) is a technique used to control the corrosion of a metal surface by making it the Cathode of an electrochemical cell.

[1] The simplest method to apply CP is by connecting the metal to be protected with another more easily corroded metal to act as the anode of the electrochemical cell."

So - as far as I can make out, for marine hull protection, the steel hull is the Cathode - so the Zinc/Aluminium must be ..... an Anode.

What fun :)

MikeJohns
01-10-2011, 06:25 AM
...........

So again, we still call the zinc anodic, while actual it is the cathode.
Bert

It depends on your frame of reference.

Look at the materials in the electrolyte; Which electrode material produces the Cations and which electrode provides the electrons to reduce the cations? Which electrode do Cations migrate to ? Why ?
Once you answer those questions you might start to see why it's not quite as clear cut a definition as a hoover when looking at a galvanic cell ;)

In an electrolytic cell with an impressed current the correct terminology is to label the electrode attached to the electron sink as the Anode (+ve) and the electron source (-ve) as the cathode.

michael pierzga
01-10-2011, 06:28 AM
Of course RWatson. The term is sacrificial anode... When Zinc is used with aluminum , zinc is the SACRIFICIAL ANODE. Material flows from the sacrificial zinc anode and is deposited on the Cathode...the hull, prop or whatever metal that is of a lower value on the index.

Its difficult to understand why the original poster has a problem with this .

.

When determining what anode you must use and which material will be the cathode, Simply consult the Galvanic table and make sure the your anode..zinc in most marine seawater cases..will be the sacrificial anode and the metal you wish to protect will be the cathode '

Zinc is at the bottom of the table...it is most Anodic at 1.25 on the index, Bronze is more cathodic at the top of the table at . 045

Zinc is the anode, Bronze is the cathode.




Metal Index (V)

Most Cathodic


Gold, solid and plated, Gold-platinum alloy 0.00

Rhodium plated on silver-plated copper 0.05

Silver, solid or plated; monel metal. High nickel-copper alloys 0.15

Nickel, solid or plated, titanium an s alloys, Monel 0.30

Copper, solid or plated; low brasses or bronzes; silver solder; German silvery high copper-nickel alloys; nickel-chromium alloys 0.35

Brass and bronzes 0.40

High brasses and bronzes 0.45

18% chromium type corrosion-resistant steels 0.50

Chromium plated; tin plated; 12% chromium type corrosion-resistant steels 0.60

Tin-plate; tin-lead solder 0.65

Lead, solid or plated; high lead alloys 0.70 2000 series wrought aluminum 0.75

Iron, wrought, gray or malleable, plain carbon and low alloy steels 0.85

Aluminum, wrought alloys other than 2000 series aluminum, cast alloys of the silicon type 0.90

Aluminum, cast alloys other than silicon type, cadmium, plated and chromate 0.95

Hot-dip-zinc plate; galvanized steel 1.20

Zinc, wrought; zinc-base die-casting alloys; zinc plated 1.25

Magnesium & magnesium-base alloys, cast or wrought 1.75

Beryllium 1.85

MikeJohns
01-10-2011, 06:34 AM
...........

So - as far as I can make out, for marine hull protection, the steel hull is the Cathode - so the Zinc/Aluminium must be ..... an Anode.

What fun :)


Yes! People get very confused because they get hung up on a definition which they misapply to the incorrect frame of reference.

CDK
01-10-2011, 06:43 AM
The principle of electrolysis is used for plating where an anode (positively charged) and a cathode (negatively charged) is placed in an electrolyte (in boating world, sea water).
Positive ions flow from the anode toward the object being plated (cathode), through the plating solution (the electrolyte), and
are deposited onto the surface of the object.

Beautifully phrased Wynand.
The real process is more complex because the electrolyte plays an active role. The acid is ionized and acts as a vehicle to transport the metal atoms, but the outcome is what you wrote.

Since the development of semiconductors the scientists have determined that electricity is transported from - to +, not the other way around, so the term positive charge is misleading: that is where the holes are.

But I do like your first sentence above, the negative electrode is the cathode.

It would be much more understandable for everyone if we used emitter and collector like for transistors, but even then the polarity issue remains because there are both NPN and PNP device.

So as pointed out in post #1 I will keep calling the zinc parts electrodes so everybody can be happy.

CDK
01-10-2011, 06:53 AM
Its difficult to understand why the original poster has a problem with this .


I have a problem with ignorant fools pretending to be experts. Try to cut&paste some brains first.

BertKu
01-10-2011, 06:58 AM
Thanks for the mental exercise guys - its always fun to retrace basic concepts and refresh minds.

So - as far as I can make out, for marine hull protection, the steel hull is the Cathode - so the Zinc/Aluminium must be ..... an Anode.

What fun :)

Yes, it is absolute fun. But lets turn it around. What is actual happening in the zinc block. If I can understand what actual is happening to the molecules and electrons, maybe we can come to an agreement. If I look at a zinc block after a few months, half of it is eaten up. Molecules and electrons have disappeared. Correct?? Can anybody explain where the electrons and molecules have gone to.

In the seawater?? Maybe, possible, could be.

Added to the hull ?? I doubt it, otherwise the hull will show this up.

So, who is going to explain what happened to those barium oxide layers on the cathode in an old fashion valve after a few years. .......A big you pardon Wikepidia, anode. My apology, we call it anode now.

Am I confused. All the old fashoned EL84, EL34, RS732 valves etc, has now the anode burning the electrons away and the cathode is ...... I am now ready for a metal institution.
bert

BertKu
01-10-2011, 07:03 AM
I have a problem with ignorant fools pretending to be experts. Try to cut&paste some brains first.

CDK, we should not get personal, this website is a fun place and we should be allowed to express our opinion, without a personal attack, even if sometimes somebody deserve it, but we should refrain from it.
Bert

rwatson
01-10-2011, 07:34 AM
the cathode is ...... I am now ready for a metal institution. bert

Thats it Bert.... a METAL institution is very appropriate. The details confuse me too.

I think the important clue is "In fact cathode polarity depends on the device type, and can even vary according to the operating mode"

The quote "But I do like your first sentence above, the negative electrode is the cathode." is therefore not necessarily accurate.

So, inspired by the METAL Institution, I read on at
http://en.wikipedia.org/wiki/Cathodic_protection

"Production of hydrogen ions: A side effect of improperly applied cathodic protection is the production of hydrogen ions, leading to its absorption in the protected metal and subsequent hydrogen embrittlement of welds and materials with high hardness. Under normal conditions, the ionic hydrogen will combine at the metal surface to create hydrogen gas, which cannot penetrate the metal. Hydrogen ions, however, are small enough to pass through the crystalline steel structure, and lead in some cases to hydrogen embrittlement.
"
Interesting, but thats is for "improperly applied cathodic protection"

So I dug further, and at
www.mrowen.com/chem12/electrochemistry/electrochemistry80.pdf

I found

"www.mrowen.com/chem12/electrochemistry/electrochemistry80.pdf"

I had to do a screen shot of the pertinent section, but essentially, Zinc oxide (not Zinc itself) gets placed on the steel - in the process.

Thanks for the inspiration Bert - its fun being an armchair researcher.

BertKu
01-10-2011, 07:58 AM
Thats it Bert.... a METAL institution is very appropriate. The details confuse me too.

IThanks for the inspiration Bert - its fun being an armchair researcher.

Hi RWatson,
I always enjoy it, when somebody has a sense of humor. It keeps us alive.
Thanks for your research, much appreciated. That basically says it all.

Bert

gonzo
01-10-2011, 09:09 AM
The more clear way of looking at all this, is to think of chemical reactions and electrical circuitry simultaneously. Sea water, whenever there is electrolysis, will free corrosive substances like chlorine. That adds to problem. On wooden boats, too large of a zinc will deteriorate the wood around the, should I say anode.

CDK
01-10-2011, 09:55 AM
Gentlemen, please pay attention.

In post #1 I made just one casual remark about why I talk about electrodes.
We are now at post #72, mostly discussing this one sentence.

My small experiment is much more important because it explains why zinc disappears sometimes faster than necessary and why electrodes with a steel strap sacrifice themselves by protecting the strap and bolts unless they are covered with paint or epoxy.

The US style electrodes, without the strap, but with copper bushings around the holes are much better designed but still need a smear of paint over the bolt heads to do what you bought them for.

viking north
01-10-2011, 10:20 AM
Thank you Gonzo for reintroducing the wooden hull problem re zincs and internal bonding of the thru hulls as i mentioned back in post #25. It was an effort on my part to change the drift of the post from sematics back to the topic as i knew from past experience what was about to evolve, re electron flow, field flow, hole flow. Any how this has been a good and very important thread on zincs and hull protection and thank you CDK for it's intro. Thruout the thread reference sites were given on info for the protection of aluminium/steel hulls, fastening of zincs, location and numbers of zincs. I installed 6 zincs on my alum. hull in addition to one on the rudder and shaft. Back to wooden hulls:would anyone like to expand on proper or popular internal electrical bonding and zincs on wooden hulls as the breakdown of wood fibers around thru hulls is no less important than metal hulls being eaten by galvanic action. Geo.

gonzo
01-10-2011, 11:59 AM
The problem with wooden hulls, is that you have thousands of metal fasteners that can't be electrically bonded. From that perspective, trunell or tree nail fastened hulls are superior.

michael pierzga
01-10-2011, 12:13 PM
CDK..?????????????????????

"The US style electrodes, without the strap, but with copper bushings around the holes are much better designed but still need a smear of paint over the bolt heads to do what you bought them for."

what are you talking about ???
__________________


What is a US style anode ? Post the technical description of a US style anode ? Are these anodes used outside of US waters ? and post all documents concerning your theory of brass fastening zinc ...or some kinda stainless fastened , "O " ring, smear of whatever compound, combination.

Post your technical documents CDK.

CDK
01-10-2011, 12:22 PM
Back to wooden hulls:would anyone like to expand on proper or popular internal electrical bonding and zincs on wooden hulls as the breakdown of wood fibers around thru hulls is no less important than metal hulls being eaten by galvanic action. Geo.

That is a problem I wasn't aware of.

My experiment revealed that in the vicinity of an active electrode, there is aggressive oxidation of steel not connected to the protected object.
I can imagine that ionized seawater is split into Na and Cl ions. The freed Na is immediately linked to oxygen, also a product of the electrolysis, but the chlorine ions may be responsible for the breakdown of wood.

Please note that electrolysis only takes place if the zinc electrode's current has a short electrical path to metal parts it is connected to. That may be a shaft or rudder if the electrode is mounted on the wood nearby, but the most logical path is to the steel strap or fasteners.

What could be the idea behind zinc electrodes on a wooden hull?

mark775
01-10-2011, 12:33 PM
Jeez, Michael - You're just picking a fight!
We fishermen not so stupid, eh Ollie? We always call da thing a zinc.
"Anode" comes from Greek "ana", which means "up" and "cathode", "kata", which means "down". (actually, way up and way down) but what about in the case of a battery being discharged, the positive terminal is the cathode, while for the same battery being recharged, the positive terminal is the anode. Since defined in terms of function, rather than structure (In my book) look at the problem in terms of current flow. If confused, remember what CDK said about a CRT. Current only flows in one direction there and IMO we can use that as a baseline, if needed.
If we can come to terms with whether current is flowing to a zinc or from it, the question is answered. Does it matter? I vote for the use of the word "zinc" to avoid the problem.
As far as the copper bushings, let's just say CDK didn't say "US style", but they are quite common that way here.
Gonzo, That thread on Wiki pedia, which I'm not even going to look at, is a direct attack, in itself, and you know it. For shitsake, lighten up and listen to CDK and we might learn something. I have lots of experience with zincs (I dare say, it would be hard for someone to have more at my age) and I didn't know about painting the bolts or the backside. I also wouldn't have known the etymology of "ana" and "kata" if it weren't for this thread, but let's move on and learn some more.

gonzo
01-10-2011, 12:46 PM
I am not sure if I read the post right. Are you saying I quoted Wikipedia?

mark775
01-10-2011, 12:47 PM
No, I just saw a thread "wikipedism" or something like that. I assumed it was just a hit on people using Wiki knowledge. If not, I apologize and will go look.

CDK
01-10-2011, 12:50 PM
CDK..?????????????????????

"The US style electrodes, without the strap, but with copper bushings around the holes are much better designed but still need a smear of paint over the bolt heads to do what you bought them for."

what are you talking about ???
__________________


What is a US style anode ? Post the technical description of a US style anode ? Are these anodes used outside of US waters ? and post all documents concerning your theory of brass fastening zinc ...or some kinda stainless fastened , "O " ring, smear of whatever compound, combination.

Post your technical documents CDK.

For you education Michael:
http://www.boatzincs.com/b-6.html

In fact the not so cleverly designed ones with an iron strap are all labeled "European style" at boatzincs.com.

viking north
01-10-2011, 01:01 PM
CDK, this was a discussion on another forum(wooden hulls, bonding, zincs) and i thought it would be a good idea to re introduce it here as the discussion seemed to be more related to zincs and metal hulls but i'm sure that many members here possibly have wooden hulls. The theory is that on wooden boats metal thru hulls should not be internally bonded to the common bond point in the hull when zincs are installed as the electrical activity associated with the resultant circuit breaks down the wood fibers at and in close proximity of the thru hulls. I could expand upon this but as a rule the more input the better. Geo.

CDK
01-10-2011, 01:37 PM
No need to expand. It is very clear what happens.
The zinc is internally bonded to an unpainted thru hull, so there is a closed circuit and the electrode starts generating a current the moment the boat reaches the water. Especially in seawater the current can be quite substantial and the electrolysis products (ions) will attack the organic material around the metal parts.

My advice is to mount zinc electrodes ON the metal parts that need protection and keep them from becoming active by meticulously painting these surfaces.

BertKu
01-10-2011, 04:10 PM
No need to expand. It is very clear what happens.
The zinc is internally bonded to an unpainted thru hull, so there is a closed circuit and the electrode starts generating a current the moment the boat reaches the water. Especially in seawater the current can be quite substantial and the electrolysis products (ions) will attack the organic material around the metal parts.

My advice is to mount zinc electrodes ON the metal parts that need protection and keep them from becoming active by meticulously painting these surfaces.

Thank you Gonzo and CDK, I have learned something. like I said in thread 58 "My conclusion is that one has to be damn carefull what kind of bolts to use when mounting the zinc. " Now I learn, that I have to paint them.

I am building a wooden boat and I was planning to connect every metal part to the sinc part. Like we were used, to have a central earth point in electronic equipment. I am never too old to learn. carry on folks, I am learning. (But don't be upset if we sometimes put some humor in the conversation)
Bert

MatthewDS
01-10-2011, 04:26 PM
Interesting discussion about the composition of marine anodes. My only comment is that anodes installed on the steel parts of the marine facilities that you folks tie up to have a very different composition.

A typical marine anode for installation on a pile or wharf is primarily aluminum, with under 10% zinc, and trace amounts of other elements like Iron, Cadmium, Silicon, and Tin.

I believe that the different composition is designed to result in a longer life, typically measured in decades, at the expense of the complete protection that a pure zinc anode would provide.

rwatson
01-10-2011, 05:07 PM
.... Thanks for your research, much appreciated. That basically says it all.

Bert

Apologies Bert, just for you and any other academics in this thread, I incorrectly read "Zinc Oxide" as the deposit on the cathode.

Blame it on my eyes and using bitmapped screen shots, but the deposit is
Zinc hydroxide Zn(OH)2

Thought I should correct my error in the interests of future generations :)

viking north
01-10-2011, 05:11 PM
Bertku, to prevent breakdown of the wood fibers at or near a wooden hulls metal thruhulls the trend amoung wooden boat owners is #1 paint the outside surface of the thruhull. #2 Do not bond the thruhull at all to the inside common bonding point. I.E. I'm not sure if you decipered that info from the comments above. I mentioned back in post #25 and again in post # 82 with the hope there would be more discussion on it as some wooden boat owners have a different take. But from all the info i have researched on the subject to bond or not to bond metal thruhulls on wooden hulls the overwelming trend seems to be not to bond. It is not a problem for me as i have a GRP hull just because of my age, finances, don't want the high maintenance but thought it was an important point for wooden boat owners and seems it does apply to your project. Geo.

Wynand N
01-11-2011, 01:16 AM
but what about in the case of a battery being discharged, the positive terminal is the cathode, while for the same battery being recharged, the positive terminal is the anode.

If we can come to terms with whether current is flowing to a zinc or from it, the question is answered. Does it matter?

Very nicely put Mark.
In electroplating as I mentioned in my earlier post, we manipulate the the positive and negative charges to the cathode and anode depending of task in hand. Getting the anode to shed some ions to the cathode (workpiece) it is usually positively charged.
However, if we want to shed from ions from the cathode - such as electro-cleaning of workpiece - the cathode gets positively charged...

In the end in my primitive view is also "does it matter?" since the results are the same. IOW, sacrificial anode (zinc) will protect the boat's more noble materials and with no sacrificial anode, something immersed on the boat will turn to an anode instead sacrificing itself to protect the next hierarchy up the galvanic scale.

BertKu
01-11-2011, 01:18 AM
Bertku, to prevent breakdown of the wood fibers at or near a wooden hulls metal thruhulls the trend amoung wooden boat owners is #1 paint the outside surface of the thruhull. #2 Do not bond the thruhull at all to the inside common bonding point. I.E. I'm not sure if you decipered that info from the comments above. I mentioned back in post #25 and again in post # 82 with the hope there would be more discussion on it as some wooden boat owners have a different take. But from all the info i have researched on the subject to bond or not to bond metal thruhulls on wooden hulls the overwelming trend seems to be not to bond. It is not a problem for me as i have a GRP hull just because of my age, finances, don't want the high maintenance but thought it was an important point for wooden boat owners and seems it does apply to your project. Geo.

Thank you Viking for the info. I misunderstood the word "bonding" as gluing, while now I understand it is electical connecting, Got the picture. Thus I should not connect the two keels to each other. But I will be running my DC motors in the keels and thus I will have to electrical isolate them from the metal keels. I better start doing some more research, as we have lightning cabling, DC motor cabling and galvanic prevention. In anyway, thanks for the hint.
Bert

BertKu
01-11-2011, 02:18 AM
CDK, you are probably the most knowledgeable on this subject. What would you do, if you were in my shoes.

I haven't made my mind up to build the keels from Stainless steel 316 or from mild steel and then powder coating them.
The experimental box I have made from mild steel.

Here is my question:

Would you electrical connect the whole lot, included the lightning down cable from the mast and both keels and make the minus of the batteries to the central earth point. Put on the powder coated keels the zincs, each keel a zinc. Put a zinc on the 30 mm shaft and a small zinc on the rudder.

OR

Would you have the DC motors and batteries and electronics floating.
Don't connect the keels to each other and have the lightning cable electrical connected to the metal keels only. We have to bear in mind that a lightning strike will have short burst, up to 40 of them per strike and up to 40.000 Ampere in each short pulse, flowing down wards and will form an electrical field. If I don't earth my electronics to the same central point I will blow the electronics , because of the energy induced by this field.

OR

Re-route the lightning surge via the mast wires and this will form a Faraday cage. Make the connection for the lightning outside the hull, to the seawater. Have the electronics and batteries floating or earth the electronics via the keels. Have the minimum zinc mounted, this in view that I will be having the boat only for a few hours per week-end into the sea.

The problem is that those three subjects are interrelated to a certain extend. Zinc and stray currents, DC motors and lightning
Bert

BertKu
01-11-2011, 02:26 AM
Apologies Bert, just for you and any other academics in this thread, I incorrectly read "Zinc Oxide" as the deposit on the cathode.

Blame it on my eyes and using bitmapped screen shots, but the deposit is
Zinc hydroxide Zn(OH)2

Thought I should correct my error in the interests of future generations :)
That cost you a beer, but apology accepted, we were not even aware of the mishap. But you are right, for those people doing the future search, it is better to have it corrected.
Bert.

Frosty
01-11-2011, 02:41 AM
This is extremely complex, I have bronze thru hulls with st /steel ball valves, acorrding to the book this is no no. I have no trouble from them but I can feel electricity of some sorts when my hands are wet yet the thru hulls are not bonded with wires but are by the seawater within it to the engine.

Behind me a friend has a wooden boat with copper bottom plate , he has stopped using anodes, they dont erode anymore, he has checked the attachments frequently with a meter yet his anodes donr erode, he is very worried.

I have no bonding to the batts and even a neg and pos batt swithching so engines are isolated.

I have halted all engine anode errosion by fresh water flushing the engines after use.

CDK
01-11-2011, 03:55 AM
Here is my question:

Would you electrical connect the whole lot, included the lightning down cable from the mast and both keels and make the minus of the batteries to the central earth point. Put on the powder coated keels the zincs, each keel a zinc. Put a zinc on the 30 mm shaft and a small zinc on the rudder.

OR

Would you have the DC motors and batteries and electronics floating.
Don't connect the keels to each other and have the lightning cable electrical connected to the metal keels only. We have to bear in mind that a lightning strike will have short burst, up to 40 of them per strike and up to 40.000 Ampere in each short pulse, flowing down wards and will form an electrical field. If I don't earth my electronics to the same central point I will blow the electronics , because of the energy induced by this field.

OR

Re-route the lightning surge via the mast wires and this will form a Faraday cage. Make the connection for the lightning outside the hull, to the seawater. Have the electronics and batteries floating or earth the electronics via the keels. Have the minimum zinc mounted, this in view that I will be having the boat only for a few hours per week-end into the sea.

The problem is that those three subjects are interrelated to a certain extend. Zinc and stray currents, DC motors and lightning
Bert

This is of course a very special case. The Faraday cage is a poor one, you don't want the deck cluttered with wires every foot.

I would bond the mast base to the keels with braided copper straps, shortest route, minimal bends, certainly no sharp angles to avoid any inductance that could cause a voltage drop during a lighting spike.
If the keels will be coated mild steel, install zinc electrodes to ensure contact with the water, if they are stainless, skip the electrodes: there are no different metals there and your boat doesn't stay in the water long enough to need protection.

You cannot leave the motors and electronics floating, they may acquire any potential vs ground during nearby lighting. If there will be a metal rudder I would use that as central ground, if not, use one of the keels for that purpose.

If the prop is bronze on a stainless shaft it gets a small zinc electrode on the prop nut or on the shaft. Paint any surface you have access to.

rgds,
Cornelis

gonzo
01-11-2011, 06:52 AM
Lightning protection is a completely different thing. To start the voltage is huge. Also, if the current can jump a mile or more, a small separation in the boat will make little difference. The current on the ground cable will produce a high magnetic field that will make other electrics act like a secondary coil in a transformer. That is why electrics get damaged on lightning strikes even if it gets grounded. The protection may save your life though.

Wynand N
01-11-2011, 06:59 AM
and this beg the question...why do one want to get this technical and complicated about anodes.

Best is to keep it simple on a boat, fit anodes where needed and have a cold frosty and fill the sails with a fair breeze. :cool:
There is an old saying; "any fool can be complicated but it takes a genius to be simple"
Having said that, why be so technical and blah, blah about having such fancy stuff/ideas and queries on boats such as Bert's post #89 (niks persoonlik nie my vriend) for a boat that will barely sees water that often?

There are millions of sail boats over a big spectrum of built materials used out on the big blue pond and mostly all of them are protected by the old trusted anode or zinc without problems and usually when there are some problems, it is a lack of insufficient anodes or foolish placement of these critters. Also, simply stick with proven bonding methods of the electrical circuits in the boat and all should be well.

KISS (please, not me) ;)

CDK
01-11-2011, 09:50 AM
Lightning protection is a completely different thing. To start the voltage is huge. Also, if the current can jump a mile or more, a small separation in the boat will make little difference. The current on the ground cable will produce a high magnetic field that will make other electrics act like a secondary coil in a transformer.

That's why the mast to keel straps must be heavy and straight.
Against a direct hit nothing helps.

michael pierzga
01-11-2011, 11:26 AM
More Voodoo statements CDK. The vessel in the picture recieved a direct hit and only suffered minor light bulb damage.

For anyone reading CDK's Caravan Park Experimental Marine Science I would recommend they first read the literature disseminated by the Metal Boat Society . This information concerning " best practice" Bonding, Anodes and lightning protection is well presented, logical , easy to understand and is widely adopted by designers, marine surveyors, insurance companies and shipbuilders.

http://www.kastenmarine.com/_pdf/mbqCref.pdf

BertKu
01-11-2011, 11:27 AM
and this beg the question...why do one want to get this technical and complicated about anodes. Because, I am making a boat with lots of electronics and electric DC motors with electronic controllers.


Best is to keep it simple on a boat, fit anodes where needed and have a cold frosty and fill the sails with a fair breeze. :cool:
There is an old saying; "any fool can be complicated but it takes a genius to be simple" It maybe true, but I am not building an sailing boat, but an electric driven boat, although it will have a small emergency sail

Having said that, why be so technical and blah, blah about having such fancy stuff/ideas and queries on boats such as Bert's post #89 (niks persoonlik nie my vriend) for a boat that will barely sees water that often? Unfortunately, even if the boat is stored at my home, I have to make provision for the electrical surges. A lightning storm will not move around my problems.


There are millions of sail boats over a big spectrum of built materials used out on the big blue pond and mostly all of them are protected by the old trusted anode or zinc without problems and usually when there are some problems, it is a lack of insufficient anodes or foolish placement of these critters. Also, simply stick with proven bonding methods of the electrical circuits in the boat and all should be well.

KISS (please, not me) ;) It is not that simple if one uses electronics. But I love to invite you for a drink or a cup of coffee or whatever and I can only learn from you. I assume you live in Houtbay, Cape Town or in that area. Durban is too far for me.
Bert

gonzo
01-11-2011, 11:29 AM
Michael: can you skip the snot and clarify what do you mean by "Voodoo statements"?

BertKu
01-11-2011, 11:42 AM
More Voodoo statements CDK. The vessel in the picture recieved a direct hit and only suffered minor light bulb damage.

For anyone reading CDK's Caravan Park Experimental Marine Science I would recommend they first read the literature disseminated by the Metal Boat Society . This information concerning " best practice" Bonding, Anodes and lightning protection is well presented, logical , easy to understand and is widely adopted by designers, marine surveyors, insurance companies and shipbuilders.

http://www.kastenmarine.com/_pdf/mbqCref.pdf

Unfortunately I must agree with CDK. Unless you have a Faraday cage type of protection, nothing helps for a direct hit. South Africa has the second highest ligthning discharges in the world. We sold and made in excess of
20 million devices for lightning surges, this is apart from all the other companies who did the same. I have been involved in insurance claims and technical issues. Only if the lightning discharge took place via the metal wires to the top of the mast from bow, aft, and sides, (Type of Faraday cage) it would have had a chance not to damage anything inside the cabin.
Bert

BertKu
01-11-2011, 12:08 PM
This information concerning " best practice" Bonding, Anodes and lightning protection is well presented, logical , easy to understand and is widely adopted by designers, marine surveyors, insurance companies and shipbuilders.

http://www.kastenmarine.com/_pdf/mbqCref.pdf

Thank you Michael, a very useful document. However it is not complete. There is no mentioning that a lichtning surge is not one surge but up to 40 bursts. This for electronics is a serious problem. A golden rule is to re-direct the surge and not to clamp or suppress the surge. Therefore I am puzzled about your attack on CDK. Like I have said before, lets not be personal and lets make it a fun website, without attacks. People should just state their opinion and nothing else. If one disagree with somebody else, it can be done in a nice way. But it is indeed a very interesting worthwile document.
Bert

gonzo
01-11-2011, 12:16 PM
I worked as a surveyor for insurance companies in Florida over two years. That is the lightning capitol of the world. I have seen many strikes where the path is erratic throughout the boat. It is possible to see the burn marks leave the grounding straps and follow the hull surface or some small wiring.

viking north
01-11-2011, 12:48 PM
I agree with Bertku, all you guys with the "KNOW" have alot of good info for us guys who need it but there are times, and often, where we have to choose and pick good criteria from all. Many times we hesitate in that we don't want to seem we are taking sides. You are well educated, informative, and experienced but at times we have to get involved in a blood bath to be part of the forum. A good example was the broken glass path i had to walk with bare feet on the, "reverse engineering thread i started". A certain amount of competitiveness is good it produces good info, but when it comes to personal attacks it embarasses us all. Not pointing out anyone, we're probably all a little guilty of this when pushed and I for one apologize if i have unknowingly done so. Just turning the light on for thought, Dont shoot the messinger, Geo.

CDK
01-11-2011, 01:46 PM
More Voodoo statements CDK. The vessel in the picture recieved a direct hit and only suffered minor light bulb damage.



The usual nonsense from Spain. You really need a shrink!

My electronics company got a major contract with the Dutch railways to protect automated railway crossings against lightning. These are very difficult objects with long control wires, high voltage lines and metal barriers that stand upright most of the time, acting as antennas. We were able to suppress all esp with spark gaps, delay circuits and Siemens varistors, but in the (rare) case of a direct hit all electronics was obliterated, cables vaporized and even the motor/worm gear exploded. The national railway company decided to replace all metal barriers with polyester ones to further reduce lightning damage.

BertKu
01-12-2011, 01:28 AM
CDK, Michael,
The problem is, when replies become very personal, people stay away from contributing and expressing their views. This in view that they do not want to be involved in arguments. I like to suggest that you both give each other some private messages and get it off your chest. But I like to see everybody, even the most timid person, to express his or her view. I may be able to learn something or use his/her idee.
bert

michael pierzga
01-12-2011, 01:39 AM
Thank you Michael, a very useful document. However it is not complete. There is no mentioning that a lightning surge is not one surge but up to 40 bursts. This for electronics is a serious problem. A golden rule is to re-direct the surge and not to clamp or suppress the surge. Therefore I am puzzled about your attack on CDK. Like I have said before, lets not be personal and lets make it a fun website, without attacks. People should just state their opinion and nothing else. If one disagree with somebody else, it can be done in a nice way. But it is indeed a very interesting worthwile document.
Bert

BertKu...when building or operating a boat , your best defense against Galvanic action , lightning damage, electrical faults, dissimilar metals...... is to follow best practice as determined by generations of specialists, boatbuilders, insurance companies and marine surveyors. This is the only way. Raw zinc anodes, mickey mouse anode bonding and non spec grounding systems revealed by CDK will not help and they are a disservice to any builder endeavoring to apply best practise.
I have been on sailing yachts struck by lighting , I have repaired sailing yachts blasted by lightning. My observation is that if you follow " best Practice" as is outlined in the literature, your boat has the best chance of escaping serious damage.

Also, I believe you inquired about using SS underwater as a Keel structure. Be wise. SS underwater is problematic. Normally I only see SS underwater when the boat is specialized...like a trailer sailer or when their is no other material more suitable .

Look at the photo. This yacht is only 4 months old...new . Observe the corrosion. SS. Oxygen depletion at the paint line. the ss in this fitting has changed from Passive to active state and its visable at the paint line. The service life of this fitting will be harsh and the service life of the sacrifical anode system will be shortened. .

Oh and BertKu, When I was a kid I worked in the shop of the German electrical engineer. .. Mr Edgar Byne. Ed wrote a booklet to educate field technicians, amateur boatbuilders and boat owners concerning general marine electrical systems. This is the link... well worthwhile printing the document to keep handy in your workshop.

http://www.smer.fi/docut/12volthandbook.pdf

BertKu
01-12-2011, 02:04 AM
BertKu...when building or operating a boat , your best defense against Galvanic action , lightning damage, electrical faults, dissimilar metals...... is to follow best practice as determined by generations of specialists, boatbuilders, insurance companies and marine surveyors.
Fully agree with you, but I am moving into unknown territory. As per example, 36 – 48 Volt on the boat. 25Kwh LifePO4 instead of a small 0.8 Kwh Lead acid battery, only 2 wires a plus and a minus, no other wires etc. etc. Thus I have to explore and listen what other people say and then make my decision. For me CDK made some very good suggestions and so did you.

Also, I believe you inquired about using SS underwater as a Keel structure. Be wise. SS underwater is problematic. Normally I only see SS underwater when the boat is specialized...like a trailer sailer or when their is no other material more suitable .
Yes, it will be a trail-able boat and you are right it will be problematic. But it is more complex. If I use mild steel, which is painted or powder coated, it does not make contact with seawater, except if I make a plan. That means normally it will oxidise at that spot, even if I mount a zinc on such a keel. If I use SS, it also will corrode, but it makes good contact.
What is better, I will chew it over for a few weeks.


Look at the photo. This yacht is only 4 months old...new . Observe the corrosion. SS. Oxygen depletion at the paint line. the ss in this fitting has changed from Passive to active state and its visable at the paint line. The service life of this fitting will be harsh and the service life of the sacrifical anode system will be shortened. .
You are right, I am fully aware of the dilemma I am in. Did they use 316 or 304 ??

Oh and BertKu, When I was a kid I worked in the shop of the German electrical engineer. .. Mr Edgar Byne. Ed wrote a booklet to educate field technicians, amateur boatbuilders and boat owners concerning general marine electrical systems. This is the link... well worthwhile printing the document to keep handy in your workshop.
http://www.smer.fi/docut/12volthandbook.pdf

Very nice and handy pdf file.
Bert

CDK
01-12-2011, 04:01 AM
CDK, Michael,
The problem is, when replies become very personal, people stay away from contributing and expressing their views. This in view that they do not want to be involved in arguments. I like to suggest that you both give each other some private messages and get it off your chest. But I like to see everybody, even the most timid person, to express his or her view. I may be able to learn something or use his/her idee.
bert

I know you mean well Bert and believe me, I ignore 99% of his ramblings, misinterpretations and outright lies, but on my turf he crosses a line.
His one and only statement on this forum I fully endorse was "I am not an engineer".:?:

But in spite of all the static in this thread, we have seen valuable contributions as well, like the way MikeJohns treats zinc electrodes and several other ones.

Btw, pointing a retired Siemens director to a 1th graders handbook about electricity (post #80) seems almost insulting to me.

BertKu
01-12-2011, 05:52 AM
But in spite of all the static in this thread, we have seen valuable contributions as well, like the way MikeJohns treats zinc electrodes and several other ones.


Indeed, it is your thread CDK, even I deviated from your topic. But in good spirit, I learned again from your thread. I would have centrally connected the whole routie-me-toetie to one central point, although I have no problem in designing electronic equipment. Even I have sailed a substantial amount of sea miles, building a boat is a different field and I have to learn and stumble over all the obstacles coming my way. CDK, I must say, that link from Michael to the pdf file http://www.kastenmarine.com/_pdf/mbqCref.pdf was very fruitful and interesting. Sometimes a foreigner express himself in a good manner, but it comes over in the wrong way. Maybe you should give it the benefit of the doubt.
Bert

CDK
01-13-2011, 07:16 AM
CDK, I must say, that link from Michael to the pdf file http://www.kastenmarine.com/_pdf/mbqCref.pdf was very fruitful and interesting. Sometimes a foreigner express himself in a good manner, but it comes over in the wrong way. Maybe you should give it the benefit of the doubt.
Bert

Of course Bert.
I rose early this morning and read Kasten's document from beginning to end. What I particularly like is the graphic representation of electrical potentials on the front page, although a simple table is probably easier to read.
In the text I found nothing new, which is not surprising because the document is 20 years old.

There are some minor flaws, like the explanation about AC voltages rising to +120 and -120V 60 times per second (should be 170V) and the colors used for wiring in 220V areas. Also the warning about graphite in grease isn't very smart.

A major flaw is how he treats zinc electrodes. Welding the iron strap is just plain wrong. This burns the few mils of zinc away and encourages fast depletion of the zinc body while reducing the ability to provide protection at further distances.
And his advice not to paint the electrode is also wrong of course, although he probably meant painting the whole electrode, not just the strap and fasteners.

It may even be beneficial to install an oversized piece of zinc and insulate part of it with an epoxy paint to keep it passive until needed, more or less like retard tablets that slowly shed their active contents. But that just occurred to me today and I haven't fully though that through.

What I find quite disturbing are the many references to ABYC, which seems to be the Moses of the boating industry. Imho people should be urged to think and reason, not blindly following instructions.

WickedGood
01-13-2011, 10:33 AM
A little History.

Most common people did not have a Vacume cleaner way bac in the 1930s and very few people had fiberglass boats. The most common use for Zinc was that to Amalgamate the Mercury in filling for teeth; That and to harden lead in cast Boolits so thet they could be fired at a higher Velocity. Velocity which is represented by the Greek Symbol v has recently been corrupted by some forginers learning electronics in American Schools that dont know that v does not stand for Voltage.

The Proper law as stated by inventor Georg Simon Ohm is that E (Voltage) is equal to I(Amps) divided by r (resistance).

If one were to amalgamate Zinc with Lead and Copper a current would flow do to Galvanic Corrosion. This theroy was proved by using a cooking Kettle in the Gally of a Wooden boat whose hull was was fastened by zinc coated clinch nails. The REsult was a fine display of Saint Elmos Fire which killed the Cook. you can all about this in the book entitled "Die galvanische Kette"

To get back on the point. A very good use of Zinc is in the fishing of a Tin Squid. It sinks at the proper rate due to its Atomic Wieght and has ashinny surface when polished with BrassO. It also will vibrate in the resonace acoustical frequency as was demonstared by Mr Carles Lightfoot and made famouse by Gordan Lightfoot in his Ballard, The Wreck of the Edmund Fitzgerald. Proof theat the End Result of Not using quality Zincs is Not a Happy One.

http://4.bp.blogspot.com/_YGLQQZTHoU0/SnhT6cA8miI/AAAAAAAAJc4/mr19Qr4n4DA/s400/lake-wreck-smiles.jpg

mark775
01-13-2011, 11:18 AM
Bizarre.
CDK, I know Siemens is huge and has worldwide and diversified presence but a long shot here... I was curious if you had anything to do with MRI?

gonzo
01-13-2011, 11:21 AM
I don't believe a cooking on a kettle will produce the voltage necessary for St. Elmo's Fire.

viking north
01-13-2011, 12:35 PM
Wicketgood, a famous newfoundland phrase,("some wicket good me son") Ya,you're a down easter, tin squid ,is that a local name for squid jigger, ours were always painted orange.
Gonzo, I,ve eaten some Mexican food cooked in a kettle that created St. Elmos fire a short time lated on exit, that combined with MontiZumas Revenge.(spelling questionable)

gonzo
01-13-2011, 12:43 PM
Next time you eat Mexican, use your toilet reading time to learn Spanish

WickedGood
01-13-2011, 12:54 PM
Monti Zumas.
The Famous inventor from the island of Velopoula?
Wow you guys are certainly Vagabonds of culture.

Monti was one of the classic pioneers of the Kettle Theroy!




http://www.playle.com/KDL/42451.jpg


How did my Rep points diminish expodentially from 37 to 20 points?
Perhaps I have inadvertanly Offended someone?

viking north
01-13-2011, 01:00 PM
Si Amigo,So i forgot to push the spacer bar, Thought it would be appropiate to sneak that in there to conform to the thread. Lifebuoy soap, now you're gettin close to home.

CDK
01-13-2011, 02:38 PM
Bizarre.
CDK, I know Siemens is huge and has worldwide and diversified presence but a long shot here... I was curious if you had anything to do with MRI?

Aha, I understand.....No!
That line was meant for BertKu, who was on their paylist. I founded my own company in '69; Siemens was one of our suppliers for various electronic parts, sometimes we cooperated for specific projects like solar energy.

BertKu
01-14-2011, 03:25 AM
Originally Posted by mark775
Bizarre.
CDK, I know Siemens is huge and has worldwide and diversified presence but a long shot here... I was curious if you had anything to do with MRI?

Aha, I understand.....No!
That line was meant for BertKu, who was on their paylist. I founded my own company in '69; Siemens was one of our suppliers for various electronic parts, sometimes we cooperated for specific projects like solar energy.

Mark775, I also have to disappoint you. I headed the electronic components and micro computer division in RSA and as such I was only involved putting up the screened cubicle, as this was part of my responsibility. As you know, each MRI is mounted in a large metal cubicle to keep any interference out. The doors have special metal strips like a comb, to ensure no electro magnetic interference can take place. Apart from a few test, the actual equipment was handled by the medical division.
Bert

BertKu
01-14-2011, 03:34 AM
A little History.

The Proper law as stated by inventor Georg Simon Ohm is that E (Voltage) is equal to I(Amps) divided by r (resistance).



I always thought E (Ego) is equal to I(insults) divided by r (resistance).

Bert

BertKu
01-15-2011, 06:30 AM
CDK, that was a lot of crap I wrote in the previous thread. Sorry that I could not resist, after everybody else started to deviate. Thus, lets go back to thread No 1 and I am pleased you brought that to our attention. I would have made many mistakes in my project, if various good information was not brought to my attention.
Bert

mark775
01-15-2011, 12:41 PM
Yes, it was a long shot - My brother installs/repairs MRIs for Siemens, is all. I thought you may have crossed paths but I seriously doubt it now!
Motecuhzoma Xocoyotzin (that's Nahuatl, or Aztec, language) Most Mexicans I have heard pronounce his name "Moctezuma" - Maybe I just havn't listened closely. Most Nahuatl doesn't exactly flow off the lips of non-Mexico City peoples. My wife smiles every time she hears a waitress pronounce "chipotle", a smoked jalapeño-like cuaresmeño, "chipolte", a knot on the head ("would you like a knot on your head salsa?"). Kinda like German technical manuals...

Carry on with the zincs, sorry.

CDK
01-15-2011, 01:35 PM
Xocoyotzin could be a medication for a nasty disease Mark.
I definitely prefer German manuals!

hoytedow
01-16-2011, 03:37 PM
http://www.archive.org/stream/diegalvanischek00ohmgoog#page/n16/mode/2up

Viel Glück!

Submarine Tom
01-16-2011, 04:10 PM
Sacrificial anodes, what a wonderful concept.

I also use them successfully on my automobile.

-Tom

hoytedow
01-16-2011, 06:18 PM
The freeze plugs in your engine are sacrificial anodes no?

viking north
01-16-2011, 06:58 PM
Not really unless you use cheap antifreeze, then they'll be sacrificed and it's usually the one where you have to remove half the engine to get at whereby the nuckles become sacrificed along with one's entry into heaven. Possibly whats happening to me right now having to go with measuring tape,flashlight and artic gear to confirm a few dimensions of my hulls lines, not working on paper,somehow I missed a station. Geo

A yacht is not defined by the vessel but by the care and love of her owner

BertKu
01-17-2011, 01:42 AM
Sacrificial anodes, what a wonderful concept.

I also use them successfully on my automobile.

-Tom

That is an intersting application. Tell us more about it.
Bert
P.S. CDK, if you allow us.

CDK
01-17-2011, 03:26 AM
http://www.archive.org/stream/diegalvanischek00ohmgoog#page/n16/mode/2up

Viel Glück!

No, thank you Hoyt, that is just as terrible.

Submarine Tom
01-17-2011, 01:02 PM
That is an intersting application. Tell us more about it.
Bert
P.S. CDK, if you allow us.

Not much to tell. Drill and tap into the frame and screw one or two in.

I don't bother on the engine.

Most applicable where salt is used on the roadway through the winter.

-Tom

CDK
01-18-2011, 03:51 AM
I've done some tests with 2 sq.ft. of steel plate and various sizes of zinc in seawater 3 ft apart, measuring both voltage and current.

The voltage is always the same (700 millivolts or 0.7 V) but the current is almost proportional to the surface area of the zinc. As little as 2 sq. inch generates approx. 15 milliamps.
Because the rate at which the zinc is sacrificed also is proportional to current, using large electrodes to protect a small amount of steel is just a waste of money: the zinc will just dissolve faster. Only using more compact, thick electrodes can prolong their life.

A relatively simple way to optimize protection is the circuit below.
The electrode is electrically insulated from the hull by using through hull bolts with nylon sleeves and collars. A suitable terminal is placed under the bolt head inside the hull.
The rheostat can now be set to a current of 10 milliamps regardless of the dimensions of the electrode. There will be adequate protection with minimal zinc loss and the gauge will show a decrease in current when it is time to replace the electrode. It will also signal paint damage by a significant current increase.

mark775
01-18-2011, 04:06 AM
That is really clever! Thanks

Ad Hoc
01-18-2011, 04:15 AM
The voltage is always the same (700 millivolts or 0.7 V) but the current is almost proportional to the surface area of the zinc.

The protection current density, Js, of all the individual surfaces, Si, yeilds the total protection current required, Is, where

Is = Sum (sigma) Js.Si

put another way, the number of anodes required, n:

n= Sum (sigma) [Js.Si]/Jmax

(Since n.Imax = Js.Si)

Then you can obtain the required amount of mass, m, of anodes.

m(zn) = 0.337S(m^2)

based upon a 2 year surface life.

For example, (from a text book example) a steel ship with a below-waterline surface area of 4500m^2 with a Js=15 mAm^-2, the current requirement is 67.5A, from the above Eqn. This gives 1517kg of zinc for a 2 year life. if the anode weighs 15.8kg the number is 96 with a current output of 0.92A.

Thus, surface area plays a major role and is directly proportional.

CDK
01-18-2011, 10:33 AM
For example, (from a text book example) a steel ship with a below-waterline surface area of 4500m^2 with a Js=15 mAm^-2, the current requirement is 67.5A, from the above Eqn. This gives 1517kg of zinc for a 2 year life. if the anode weighs 15.8kg the number is 96 with a current output of 0.92A.

Thus, surface area plays a major role and is directly proportional.

That is quite a lot of zinc John, half the weight of my boat.
Does the text book specify a paint system? For an epoxy painted hull I think 15 mA/m^2 is rather high.

Submarine Tom
01-18-2011, 12:48 PM
Brilliant CDK!

I think you get a gold star AND move to the front of the class.

(For those of you who like to read into these things, there is no sarcasm expressed or implied in my compliment.)

-Tom

MikeJohns
01-18-2011, 04:43 PM
You allow for a current density within a range of 10 to 40 ma/m2. Ocean going vessels need a lot less than coastal vessels. We use 20ma/m2 for inshore commercial.

For Johns ship above I would have specified 1.6 tonnes of zinc ! I use 730 Ahrs/kg for the zinc andodes manufactured here.

MikeJohns
01-18-2011, 04:48 PM
Not much to tell. Drill and tap into the frame and screw one or two in.

I don't bother on the engine.

Most applicable where salt is used on the roadway through the winter.

-Tom

That wont work very well Tom.
It will protect a very small radius within a conductive film of electrolyte. You need ion exchange for cathodic protection, there's no other way for the zinc to give up its electrons to the car body.
The protection is limited to the area of ion exchange. The problem is that the wet film is so thin that you'll only get protection just below and maybe if you're lucky, for an inch around the periphery of the zinc block.

Submarine Tom
01-18-2011, 05:02 PM
I wonder then why the zincs are corroding and my vehicle isn't.

The theory says the least noble metal will be the one that oxidizes making it sacrificial and preserving anything bonded to it.

They use it, effectively, on pipe-lines all the time.

Are you getting confused with galvanizing?

-Tom

MikeJohns
01-18-2011, 05:51 PM
I wonder then why the zincs are corroding and my vehicle isn't.

The theory says the least noble metal will be the one that oxidizes making it sacrificial and preserving anything bonded to it.

They use it, effectively, on pipe-lines all the time.

Are you getting confused with galvanizing?

-Tom

Remember you also need reduction not just oxidation.

The ions have to migrate through an electrolyte. A thin film such as a wet under-surface of a vehicle won't allow them to migrate very far at all.

Pipelines are protected with Zincs when they are buried or immersed. They cannot be effectively protected that way in the atmosphere. The zinc will just oxidise it's surface and passivate.


If you completely isolated your car zinc block and subjected it to the salt road spray it will self corrode. Also your car is painted with a good underseal, try the same exercise with areas of that underseal scraped off in various locations ;).

BertKu
01-19-2011, 01:09 AM
You allow for a current density within a range of 10 to 40 ma/m2. Ocean going vessels need a lot less than coastal vessels. We use 20ma/m2 for inshore commercial.

For Johns ship above I would have specified 1.6 tonnes of zinc ! I use 730 Ahrs/kg for the zinc andodes manufactured here.

John and Mike,

Now let see whether I have it right.

If I paint that boat below the line, I have to use 1600 Kg. However if I have a bare non painted bottom part, I also have to use 1600 Kg of Zinc.

Could you please elaborate on this? Or am I really ready for the Metal institution?.
Bert

Ad Hoc
01-19-2011, 01:17 AM
If I paint that boat below the line, I have to use 1600 Kg. However if I have a bare non painted bottom part, I also have to use 1600 Kg of Zinc.


Bert

No, the example, shown here:


For example, (from a text book example) a steel ship with a below-waterline surface area of 4500m^2 with a Js=15 mAm^-2, the current requirement is 67.5A, from the above Eqn. This gives 1517kg of zinc for a 2 year life. if the anode weighs 15.8kg the number is 96 with a current output of 0.92A.


..this vessel has a surface area of 4500m2.

So if your boat has this amount of surface area (ie a super tanker!!) then yes. But some how i think your boat is a bit smaller..yes?? :p

The underwater surface area is the key input to calculating how much you need.

So, for example, if your boat is say 20 tonne displacement this equates to roughly 7.5m2 surface area, under the water. If, given all things being the same, this is pro rata: 7.5/4500 x 1600 = 2.7kg of zinc

BertKu
01-19-2011, 01:38 AM
Bert

No, the example, shown here:



, this is pro rata: 7.5/4500 x 1600 = 2.7kg of zinc

Hi John,

No, we have a misunderstanding.

I mean, I always thought that there is a difference between a 100% properly painted below the waterline, without scratches and contact with the electrolite (seawater) and if the full non painted hull surface area is exposed to the seawater.

I am under the impression that in the 1st instance, the zinc will be less "eaten up" , while in the second instance, the zinc will be eaten up as per your calculation.

By the way, I have only approx 10m^2 surface area and indeed your zinc weight is spot on, should I make a metal boat. But it will be a wooden boat with only approx 5m^2 powder coated metal surface below the waterline. Keels only. I need thus very little zinc. I am buying a special round clip-on zinc for my 30 mm shaft.

But for the powder coated keels I am listening very careful to You, CDK and Mike's arguments. At present the stand is that CDK is ahead, I am inclined to follow his advice at present.
Bert

Joakim
01-19-2011, 01:44 AM
So, for example, if your boat is say 20 tonne displacement this equates to roughly 7.5m2 surface area, under the water. If, given all things being the same, this is pro rata: 7.5/4500 x 1600 = 2.7kg of zinc

I guess you meant 75 m2 surface area (and 27 kg), since my 3 tonne sailboat already has 16 m2.

But there must be some kind of assumption about the paint condition. Perfectly epoxy painted steel will not need that much, if any, current.

BertKu
01-19-2011, 02:03 AM
I wonder then why the zincs are corroding and my vehicle isn't.

The theory says the least noble metal will be the one that oxidizes making it sacrificial and preserving anything bonded to it.

-Tom

Tom, I am inclined to agree with you. When it rains and at the coast, it has salt in the air, the automobile car body will be getting moisture all over the bodywork. Thus in that case the electrolite is present, and thus your bodyworks is protected.
As soon the sun is there and the body is dry and warmed up and no moisture is around, indeed the zinc will only protect a small area, only there where maybe some salt/sand is kicked up from the road. Should you be living inland, in that case only the moisture from the sand/salt thrown from under your car by the wheels will be the electrolite. Thus why should your complete car not be protected?. This proves your point.
Bert

BertKu
01-19-2011, 02:08 AM
I guess you meant 75 m2 surface area (and 27 kg), since my 3 tonne sailboat already has 16 m2.

But there must be some kind of assumption about the paint condition. Perfectly epoxy painted steel will not need that much, if any, current.

Joakim, AdHoc has my boat weight and dimensions. He meant, 2 Tonnes instead of 20 tonnes and 7,5 m2., thus 2,7 kg is correct.
Bert

michael pierzga
01-19-2011, 02:27 AM
Ad Hocs formula sounds like what is commonly used. Ive just re anoded an 20 year old aluminum hull under guidance of MgDuff...100sq meters underwater surface. Sea water. 100\4500 x 1600 = 35.5 kg The epoxy barrier coated , international Micron antifouled hull carries six, 7kg 220mm zinc pie plate anodes , a prop anode, plus a 4 strap anodes on the thrusters and two strap anodes inside the sea chest. There is no exposed propeller shaft. The anode stock on this vessel lasts 4 years, with the forward high water velocity pie plate anodes and the thruster anodes eroding first , sea chest strip anodes and prop anode are replaced yearly

http://www.mgduff.co.uk/leisure-craft/fitting-instructions/aluminium.html

Submarine Tom
01-19-2011, 02:41 AM
Lets get this branch (http://www.boatdesign.net/forums/open-discussion/will-bonded-zinc-protect-my-automobile-36340.html#post436296) off CDK's thread.

I'll start a new one.

-Tom

CDK
01-19-2011, 04:04 AM
With no bare metal exposed, there will run no current between the electrodes and the hull, so the zinc will not be active and it is irrelevant what amount of zinc is installed.

I think (?) the guidelines specifying current and zinc mass are based on experience and statistical data on paint flaws, scratches etc.
But these guidelines are pretty old and do not differentiate between paint systems. They may even assume protection by tar instead of modern paints.
Of course there will always be conductive patches on a hull as large as a supertanker, but why should you apply the same criteria to yacht?

Also, they are based on conventional electrode mounting where -as pointed out earlier- the zinc protects its own iron parts and depletes faster than necessary.

BertKu
01-19-2011, 09:34 AM
With no bare metal exposed, there will run no current between the electrodes and the hull, so the zinc will not be active and it is irrelevant what amount of zinc is installed.

I think (?) the guidelines specifying current and zinc mass are based on experience and statistical data on paint flaws, scratches etc.
But these guidelines are pretty old and do not differentiate between paint systems. They may even assume protection by tar instead of modern paints.
Of course there will always be conductive patches on a hull as large as a supertanker, but why should you apply the same criteria to yacht?

Also, they are based on conventional electrode mounting where -as pointed out earlier- the zinc protects its own iron parts and depletes faster than necessary.

That makes common sense.

Can I assume correctly. We are going to store a boat out of the sea, somewhere in the backyard, but close to the sea. Should it rain and there is sufficient salt in the air, the metal will still be rusting, if not protected by zinc. Assuming, it has no cover over the boat. We refer to the previous info, about the automobile in Canada.
Bert

MikeJohns
01-19-2011, 04:41 PM
That makes common sense.

Can I assume correctly. We are going to store a boat out of the sea, somewhere in the backyard, but close to the sea. Should it rain and there is sufficient salt in the air, the metal will still be rusting, if not protected by zinc. Assuming, it has no cover over the boat. We refer to the previous info, about the automobile in Canada.
Bert

The automobile case as I explained earlier is a nonsense. it cannot protect anything other than the immediate adjacent surface, (a few mm in you are lucky) if the film is a reasonable electrolyte (not fresh water).

Exactly the same goes for the boat ashore. In fact in rain water the zinc surface will usually passivate and become more noble than the adjacent steel not that that makes any difference to this case.

There is apparently some serious misunderstanding as to how cathodic protection actually works.

viking north
01-19-2011, 05:02 PM
Who'd ever think the zinc topic would be still ongoing. It's a very complicated subject, and i have to take my hats off for the effort you guys are putting into it. I have a related question. The subject so far relates to corrosion protection using the passive action of zincs(passive meaning corrosion control without an actual electrical/electronic device doing the actual corrosion control) Some 100 years back i helped a friend of mine install an active device (control box) wired to some sort of metal blocks that were epoxied to the steel hull of his big power yacht.I do recall him saying they use similar set ups on big ships and that it was expensive. I've often wondered especially when i had an aluminium hull does that setup prove to be effective and if it is still available and used today. Geo.

A yacht is not defined by the vessel but by the care and love of her owner

hoytedow
01-19-2011, 05:37 PM
I have found it very interesting, and humbling.

MikeJohns
01-19-2011, 07:05 PM
Yes impressed current protection works very well (when its working).

BertKu
01-20-2011, 01:23 AM
The automobile case as I explained earlier is a nonsense. it cannot protect anything other than the immediate adjacent surface, (a few mm in you are lucky) if the film is a reasonable electrolyte (not fresh water).

Exactly the same goes for the boat ashore. In fact in rain water the zinc surface will usually passivate and become more noble than the adjacent steel not that that makes any difference to this case.

There is apparently some serious misunderstanding as to how cathodic protection actually works.

Hi Mike,

I am never too old to learn. If we do misunderstand the cathodic protection actual work, could you explain why in many instances, it is working on an object, if you say it is nonsense.

Can you explain why the one object is getting rusted and the other who has no protection get rusted on the scratches during dew and low hanging clouds and rain, which seem to have some salt content close to the coast.

I believe that the very thin layer of dew is sufficient to make the cathodic protection actual work. Dew get everywhere.

I do know the capacitance principle, whereby two plates are being mounted on an object and by alternating the potential, the object becomes the dialectricum. I am not too sure how well that one is working, but cathodic protection could work on a boat stored at home, close to the coast. Do you really believe that the electrolyte layer is too thin? I should take an Ohm meter and measure whether we actual have a conductive circuit.

Will let you know, when we have dew.
Bert

Ad Hoc
01-20-2011, 01:44 AM
..Some 100 years back i helped a friend of mine install an active device (control box) wired to some sort of metal blocks that were epoxied to the steel hull of his big power yacht.I do recall him saying they use similar set ups on big ships and that it was expensive...

As Mike has noted, these impressed current systems do work, sometimes! They are mostly used on steel hulls, the main problem though, is the electrical supply. If the boat has shore supply, that's great, simply because of the amount of current required day in day out.

Take a typical 10m boat and assume the current density of around 50mA/m2, this would nominally consume around 1.5amps, ir 250amp hours per week! Hence very large batteries and a charging system would be need...heavy and expensive..is it worth it? So these systems are generally used to protect small items such as an out-drive.

BertKu
01-20-2011, 01:53 AM
A yacht is not defined by the vessel but by the care and love of her owner

Hi Geo, I agree with your statement.

That black box could be the alternating ( approx every 1 second) of the potential of the two electrodes. You alluminium yacht will be come the dialectric . By alternating, the electrons are being accumulated at the one side, and in another second at the otherside. Hereby preventing the object (Your yacht, which is the dialectric) from corroding. I sometimes had the suspicion that the big metal blocks were actual zinc, but never bothered to check.
P.S. The plates has to be reasonable large, but I am not willing to put my head on the block that it actual is working. I have one unit here at home. I will one day disolve the epoxy and see what is inside.

MikeJohns
01-20-2011, 02:02 AM
Hi Mike,

I am never too old to learn. ..........
I believe that the very thin layer of dew is sufficient to make the cathodic protection actual work. Dew get everywhere..........

Do you really believe that the electrolyte layer is too thin? .......

Will let you know, when we have dew.
Bert

You don't need to and perhaps just look outside your terms of reference for a minute. There are lots of rusting galvanised items.

Look at a galvanised sheet of corrugated steel roofing with a patch where the zinc is worn off. It's almost completely covered in zinc, so it has a massive surface area of Zinc protecting a small bare patch of exposed steel. But you'll observe that small patch of steel rusting happily away when the sheet of roofing is wet.
In a coastal environment it rusts even faster. Dip it in the ocean and it stops rusting, in fact it gets deposited material on the bare steel surface and the zinc erodes.

That's the most obvious illustration I can suggest.

If you really want to understand cathodic protection you need to understand both properties of materials and enough chemistry to fully understand redox reactions. It's never a case of simply believing something, it needs to be a sensible hypothesis for starters. That hypothesis should then also be clearly observable.

It would be really nice if it worked, but it is nonsense sorry.

BertKu
01-20-2011, 02:17 AM
As Mike has noted, these impressed current systems do work, sometimes! They are mostly used on steel hulls, the main problem though, is the electrical supply. If the boat has shore supply, that's great, simply because of the amount of current required day in day out.

Take a typical 10m boat and assume the current density of around 50mA/m2, this would nominally consume around 1.5amps, ir 250amp hours per week! Hence very large batteries and a charging system would be need...heavy and expensive..is it worth it? So these systems are generally used to protect small items such as an out-drive.

John, is there a reason why you use such a high value of 50 mA/m2 I thought that 5 - 10 mA/m2 is more than enough. Except if the boat is a neglected boat with lots of scatches and paint pealed off. Is there a reason?
Bert

BertKu
01-20-2011, 02:32 AM
Look at a galvanised sheet of corrugated steel roofing with a patch where the zinc is worn off. It's almost completely covered in zinc, so it has a massive surface area of Zinc protecting a small bare patch of exposed steel. But you'll observe that small patch of steel rusting happily away when the sheet of roofing is wet.
In a coastal environment it rusts even faster. Dip it in the ocean and it stops rusting, in fact it gets deposited material on the bare steel surface and the zinc erodes.

That's the most obvious illustration I can suggest.



Thanks Mike,
Your point is taken. Good example. Bert

CDK
01-20-2011, 03:05 AM
As Mike has noted, these impressed current systems do work, sometimes! They are mostly used on steel hulls, the main problem though, is the electrical supply. If the boat has shore supply, that's great, simply because of the amount of current required day in day out.

Take a typical 10m boat and assume the current density of around 50mA/m2, this would nominally consume around 1.5amps, ir 250amp hours per week! Hence very large batteries and a charging system would be need...heavy and expensive..is it worth it? So these systems are generally used to protect small items such as an out-drive.

Would there be commercial interest in an autonomous cathodic protection system where maintenance is limited to replacing just a single "zinc electrode" while still protecting the hull from bow to stern?

For a large vessel the electrode would in fact be an array in a convenient location near the waterline.

BertKu
01-20-2011, 08:39 AM
Take a typical 10m boat and assume the current density of around 50mA/m2, this would nominally consume around 1.5amps, ir 250amp hours per week! Hence very large batteries and a charging system would be need...heavy and expensive..is it worth it? So these systems are generally used to protect small items such as an out-drive.

Hi John,
I am not criticising your finger slip on the keyboard (1,5 Amps should read 0.5 Amp it also happens sometimes to me), but I would say: 10 m2 x 10mA/m2 = 0.1amps x 7 days x 24 hours is only 16.8 Amperhour. A solar panel could deliver that per week. But the normal zinc protection is more practical and the energy from the solarpanel could be used for something more useful. Except if it is proven that 10 mA/m2 is sufficient and one like to waste energy.
Bert

CDK
01-21-2011, 03:58 AM
Hi John,
I am not criticising your finger slip on the keyboard (1,5 Amps should read 0.5 Amp it also happens sometimes to me), but I would say: 10 m2 x 10mA/m2 = 0.1amps x 7 days x 24 hours is only 16.8 Amperhour. A solar panel could deliver that per week. But the normal zinc protection is more practical and the energy from the solarpanel could be used for something more useful. Except if it is proven that 10 mA/m2 is sufficient and one like to waste energy.
Bert

Actually the energy demand is much less Bert.
Supplying John's 1.5 Amps to a metal hull can be done with a potential of no more than 0.5 V.
The demand in a week would be 1.5 x 0.5 x 24 x 7 = 126 Watt/hours. Taken from a 12V battery that would be slightly more than 10 AH.

Your example would use 0.1 x 0.5 x 24 x 7 = 8.4 Watt/hour or 0.7 AH from a 12V battery and a very simple voltage converter.

I omit the 10% converter loss here because it is not significant for the calculation.

BertKu
01-21-2011, 04:23 AM
Actually the energy demand is much less Bert.
Supplying John's 1.5 Amps to a metal hull can be done with a potential of no more than 0.5 V.
The demand in a week would be 1.5 x 0.5 x 24 x 7 = 126 Watt/hours. Taken from a 12V battery that would be slightly more than 10 AH.

Your example would use 0.1 x 0.5 x 24 x 7 = 8.4 Watt/hour or 0.7 AH from a 12V battery and a very simple voltage converter.

I omit the 10% converter loss here because it is not significant for the calculation.

You are totally right. I was not thinking in line of voltage regulator down to 0.5 Volt, but more thinking in line with protection of oil pipelines we did with solar cells. Certainly an efficient voltage regulator would be a good solution.

CDK, when should one go for forced protection and when should one go for natural protection. I assume if a yacht is an harbour and there are lots of stray currents around, one would opt for forced protection.
Bert

CDK
01-21-2011, 08:50 AM
CDK, when should one go for forced protection and when should one go for natural protection. I assume if a yacht is an harbour and there are lots of stray currents around, one would opt for forced protection.
Bert

If you buy a fiberglass boat like a Searay with stern drives nowadays, it comes standard with a Mercathode system (funny name huh, not Meranode), so manufacturers recognize its usefulness.

If I were responsible for the exploitation of a large ship I would go for an active system because having divers replace zinc electrodes every two years seems like an expensive operation to me. For a steel yacht taken out every few years for an anti-fouling coat it would depend on the installation cost of such a system.

In principle an active system needs not be more expensive than zinc, but you know how the boating world is organized: if it works better and/or has a display, it costs a fortune.

SheetWise
01-21-2011, 08:57 PM
I would like to thank the entire community for a very pleasant read. It would never have occurred to me that I would read an eleven page "discussion" on cathodic/anodic corrosion. My ear is tuned to CDK's voice, and I (as always) appreciate the methodical clarity brought to subjects he is interested in.

Thank you all. (Maybe you're not done ;)

MikeJohns
01-21-2011, 09:54 PM
The Impressed current systems need reference electrodes, they may vary their voltage and current to correctly polarize the protected metal relative to seawater.

The voltage between the hull and the surrounding seawater is maintained at around 1 volt (I think the recommended minimum is 0.95V now and no longer 0.85V). Note that is the seawater hull minimum potential difference over the protected area.

The common Platinum electrode material is usually deposited on titanium ( from memory) and these electrodes are run at up to 10 volts to achieve active protection ( that's the limit for a the bonded titanium_Platinum electrode). Other Electrodes are run at higher voltages. The amount of current will depend on the area protected and the paint film condition. Recommendations are for active systems that can accommodate 10% paint film damage.

This is one reason why zincs are so good, they will protect any amount of bare steel in return for a reduced life. An active protection system will just run out of it's ability to supply energy and the hull will corrode.

The resistance of Seawater with which these systems can work can vary up to 6 Thousand Ohms at 3m radius. An electric field is present in the seawater around the active electrodes encompassing the hull, and with concentrations at the paint film discontinuities. Film formation alters the surface properties both inorganic and bio-organic films can passivate a surface or reduce it’s relative potential significantly, this occurs an both the hull and the active electode, so much larger voltages are required than you would initially expect.

This is not a trivial simple application and it is not the same game as a passive Anode. There have been some notable and expensive failures with impressed current systems and they have their limitations.

Ad Hoc
01-21-2011, 10:25 PM
This is not a trivial simple application and it is not the same game as a passive Anode. Their have been some notable and expensive failures with impressed current systems and they have their limitations.

Agreed. We have had some of these "failures" on our boats..especially around waterjets. It is not a plug and play solution.

SheetWise
01-22-2011, 05:37 AM
This is not a trivial simple application and it is not the same game as a passive Anode. There have been some notable and expensive failures with impressed current systems and they have their limitations.

Not trivial. I first became aware of these systems talking to the crew that preserves the Star of India at the San Diego Maritime Museum (an iron hull tall ship). That was the spark that led me to follow the entire thread.

CDK
01-22-2011, 11:35 AM
The voltage between the hull and the surrounding seawater is maintained at around 1 volt (I think the recommended minimum is 0.95V now and no longer 0.85V). Note that is the seawater hull minimum potential difference over the protected area.

The common Platinum electrode material is usually deposited on titanium ( from memory) and these electrodes are run at up to 10 volts to achieve active protection ( that's the limit for a the bonded titanium_Platinum electrode). Other Electrodes are run at higher voltages. The amount of current will depend on the area protected and the paint film condition. Recommendations are for active systems that can accommodate 10% paint film damage.

This is one reason why zincs are so good, they will protect any amount of bare steel in return for a reduced life. An active protection system will just run out of it's ability to supply energy and the hull will corrode.

Seawater has a resistance of around 6 Thousand Ohms at 3m radius. An electric field is present in the seawater around the active electrodes encompassing the hull, and with concentrations at the paint film discontinuities. Film formation alters the surface properties both inorganic and bio-organic films can passivate a surface or reduce it’s relative potential significantly, this occurs an both the hull and the active electode, so much larger voltages are required than you would initially expect.



You made some lucid remarks about zinc electrodes, but now you've taken a wrong turn!

First of all, the conductivity of seawater is assumed to be 5000 millimhos/meter or 5 Siemens/m (ITT Reference Data for Radio Engineers). That gives a theoretical resistance of 0.2 ohms per meter or 0.6 ohms for 3 meters. Seawater doesn't conduct as good as metal, but it comes pretty close. The value is used among other things for determining the efficiency as a ground plane in telecommunications.

Measurements with a multimeter are meaningless because of electrochemical activity at the probes and their small size. The calculation of resistivity between 2 points is a complex integral, analog to an infinite number of wires between these points with increasing length. I don't want to bother anybody with it here.

A zinc electrode in seawater generates an electric potential of 0.5 to 0.7V towards ferrous metals, a lot less towards aluminum. If this is the voltage range we are happy with, I do not see the need of increasing the voltage in an impressed current system.
Active systems with platinum or palladium electrodes and a silver-chloride reference need a higher voltage because they are very small due to the materials price. With a lump of platinum the size of a zinc electrode 0.5 volts would be enough to perform like zinc does.

The Mercathode system demonstrates the above. It has, to say it politely, a rather limited lifetime. If you dissect a unit after just a few years of (assumed) service, you'll find a hole in the reference electrode where is once was soldered to its wire. Especially if it has been staring at two stainless props its life is sheer agony.
The electronics involved are stone age technology where the electrode voltage is increased until the reference value is reached. With a gaping hole in the silver reference electrode the noble one is near the + Battery voltage, which is lethal even for one micron of platinum.

But there is a better way to do things.
The electronic circuit must be a switch mode converter delivering a minimal voltage over a current range from 0 to the required current based on the surface to be protected, whether this is 10 milliamps /sq. meter or 50 is a matter of personal preference.
I've measured 30 mA for an 8 sq.cm. bare surface, so 10% paint damage is an impossible goal unless we are discussing toy boats. A large zinc electrode of 200x200 mm gives 1.5 Amp and dies in the process (it looses 0.82 grams for each Amp/hour.

There is absolutely no need for a reference electrode, that is just complicating things. The AgCl electrode is nice for a measurement but must stay in the water as short as possible, subsequently rinsed, dried and stored.
The converter I described above should have a simple current measuring circuit. Again it is a matter of personal taste to choose an old fashioned analog instrument, a numeric display or a flashing "ATTENTION, CURRENT LIMIT EXCEEDED".
A drop in current means bad wiring or a lost electrode, an increase means the integrity of the paint layer has become questionable.
Boat used in both fresh water and at sea need two current markers because the conductivities are different. Or a simple switch if two markers are confusing.

And then there is the electrode.
No metals destined for women's jewelry, but something cheap and simple, so making a 3 inch electrode surface doesn't flatten your wallet.
A material that conducts well and (almost) doesn't take part in electrochemical processes. Used to deposit zinc on steel, gold on copper, to split water into H2 and O.
Yes: CARBON!
Sintered on a copper substrate (or copper deposited) and potted in a resin and a glass filled cup. The bottom has a threaded hole and an O-ring groove so you can simply screw it on an insulated through hull stainless bolt.

Does this exist? I don't know.
If I could figure this out on a Saturday morning while painting a ceramic floor there must be dozens of guys who figured it out in the past.
If not, someone should start doing so on Monday morning.

viking north
01-22-2011, 02:40 PM
Thanks all, i have not come back on thread since i queried the merits of the active system back on post #150 but i have been following along and you have more than answered my question thanks. I can see there are merits to update this system using more modern control circuits and materials if somewhere lurking out there it is not already on the market. It sounds like it could be more effective with less guesswork if it could be made reliable. I do know there is a similar system being marketed to protect automobiles but have no info wheather it is reliable or not. Actually i think i'll search that down and look up the consumer report on it and get back but meanwhile if someone has that info already by all means save me the time. Tnx. Geo.

A yacht is not defined by the vessel but by the care and love of her owner.

MikeJohns
01-23-2011, 03:49 PM
You made some lucid remarks about zinc electrodes, but now you've taken a wrong turn!........the conductivity of seawater is assumed to be 5000 millimhos/meter..... That gives a theoretical resistance of 0.2 ohms per meter or 0.6 ohms for 3 meters.


Yes sorry not pure seawater, I pulled the figure from a local active protection system blurb and that's the worst case quoted Which is brackish estuarine. Looking again at that article and they work on up to 50 volts with an easily replacable graphite electrode ! So I think you are re-inventing the wheel.

The reference electrode allows the system to adjust for variation in operational parameters (water resistivity, surface films, surface passivation ). A lot of research has been conducted on these systems and the accepted level of effective protection which is to polarize the hull at least 0.85 V to 0.95V above the surrounding seawater. ),95 V is now the suggested minimum for low oxygen seawater.

To force a current into a surface is the wrong approach. it's the polarisation that you want in this case not the current. It's not the same process as the Zinc galvanic cell which is an electrochemical cell working on ion exchange. The Impressed system polarises the surface by shifting the voltage relative to sea water.

So consider that for all the systems that are installed using Platinum, graphite, even low wastage alloyed iron active electrodes why do they run their voltages so high when they are simply polarizing the hull by .85 to .95 Volts ?

As for Zincs and the level of damage they can protect, you know when you've had a grounding and the zinc lasts longer than you would expect because of film and calcareous deposit formation on the protected surface. There's an initially high current which quickly drops over a few hours so the zincs last a lot longer than you would initially think.

gonzo
01-23-2011, 07:31 PM
How does the voltage prevent electrolysis between dissimilar metals? If they are all biased at the same voltage, the potential difference between them is the same.

CDK
01-24-2011, 04:19 AM
How does the voltage prevent electrolysis between dissimilar metals? If they are all biased at the same voltage, the potential difference between them is the same.

By applying a negative voltage on the electrodes (either zinc or impressed current), the hull gets a positive potential against the surrounding water. If the potential is greater than that caused by dissimilar metals, there will be relative differences, but the absolute value remains positive, so galvanic corrosion is inhibited.

On a stern drive equipped with a working Mercathode system, the zinc electrodes present (trim tabs, zinc on anti-cavitation plate) do not wear because with the water slightly more negative than the zinc, there is no electrolysis.

It is like a lamp drawing current from a battery under charge: as long as the charger voltage is above the battery voltage, current flows directly from the charger to the lamp.

viking north
01-24-2011, 08:46 AM
CDK, excellent explanation with the battery charger, battery and lamp combo. The batterys integrity(hull and associated parts) is maintained as long as the charger is the supplier of the wants of the lamp.(galvanic wants of the hulls dissimilar metals) It makes the operation of the system so understandable. Basically the charge set up on the hull nullafy the wants of dissimilar metals associated with the hull to eat each other. The meat on the cage floor satifies the lion from eating it's caretaker. As promised above I am doing some research on modern systems on the market and have located one that sounds like it is designed for smaller craft ( up to a 30ft alum. hull) but as yet have not done any research into consumer reports on it's effectiveness or reliability. Once again thanks all for your input into this alchemi subject. Geo

gonzo
01-24-2011, 09:05 AM
OK, but the potential difference between dissimilar metals remains the same. That is like biasing AC with DC.

CDK
01-24-2011, 09:17 AM
OK, but the potential difference between dissimilar metals remains the same. That is like biasing AC with DC.

Not quite the same Gonzo.

The differential does exist, but the galvanic action is ruled by the potential vs. the electrolyte (water). Example: If a piece of steel is kept at 1 V positive, a connected piece of zinc is still at 0.4 V positive, so no galvanic action takes place.

gonzo
01-24-2011, 09:55 AM
What happens to a stainless shaft in an aluminum housing? They are both electrically connected so the bias would be the same. However, the potential difference between them remains the same. I may be missing something. I thought that bias protection only worked if you biased the lower metal in the scale.

michael pierzga
01-24-2011, 11:50 AM
No metal to metal contact is allowed between SS and aluminium in a shaft run. It would disintergate .

"O" rings, Lip seals, cutlass bearings , oil baths ,are always between the alum and SS.

The reason why you use grounding brushes on a prop shaft is because the SS shaft has no, or very poor, electrical connection to the hull. It is floating.

CDK
01-24-2011, 12:05 PM
Yes, both have the same bias, but the aluminum isn't happy with that because it wants to be half a volt lower, so it starts emitting ions into the electrolyte, thereby lifting the potential of the whole. The current flowing determines the rate at which the Al dissolves.
If another source emits ions already at a higher rate and the potential is higher than the target of the Al, the current flow stops.

Analogies: swimming with the tide, driving downhill, eating with a full stomach etc.

The opposite is also true. Stray currents from nearby objects with inverse polarity make your zinc disappear faster.

gonzo
01-24-2011, 12:14 PM
Michael: Shafts and housings make contact always. The gears, bearings, etc are all in contact. Many are press fit. I've yet to see an outboard or outdrive with a cutlass bearing or grounding brushes. Seems like you just make stuff up.
CDK: So the bias only works if the metals are isolated?

michael pierzga
01-24-2011, 01:48 PM
This is a lip seal !!

Ive yet to see a lower unit without a lip seal protected oil bath gear box. The lip seal insures that there is no electrolyte submerged SS to aluminium contact and keeps the gear box full of oil . Its possible that you operate your vessels without lip seals and sea water in the lower units, but this is not normal practice and will greatly reduce the service life.

CDK
01-24-2011, 02:56 PM
Michael: Shafts and housings make contact always. The gears, bearings, etc are all in contact. Many are press fit. I've yet to see an outboard or outdrive with a cutlass bearing or grounding brushes. Seems like you just make stuff up.
CDK: So the bias only works if the metals are isolated?

Gonzo, please take my word for it that with the proper bias from an external source, any combination of metals is protected against galvanic corrosion.

The actual process of electrolysis, involving Zn+ or Al+ ions being released and reacting with negative ions in the electrolyte while electrons travel through the metal junctions is too complex for this thread and confusing for most readers, so I took some shortcuts in my last answers.

Re: the outboard shaft.
When running there is an oil film insulating bearings, gears and ultimately between the stainless shaft and alloy housing.
When not in use (most of the time), the oil film is broken and there may or may not be an electrical path between shaft and housing. Such a path also exists between the shaft and an aluminum prop.

Because the bare surface of the shaft is very small, there is only minimal corrosion of the alloy parts.

viking north
01-24-2011, 04:24 PM
Oh My the boys are at it again, the KISS principle, the metals on the lower end of the galvanic scale are not robbed of it's structure because there is an overriding source supplied by the outside active device. The caretaker is not eaten because an ample supply of raw meat is readly available.
CDK confirmation on my take, all the different nobality levels of metals present will feed off the supply to different amounts in that it satisfys their differences of potentials thus prevents them from feeding off each other. Is my general drift ok here. Geo.

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