Barnacles on Anode

[Pasarell]

Coreng

Sorry to miss all the fun on this topic - I've been away at the annual NACE corrosion engineering conference in Houston
I don't think Coreng helps himself with his poor English but isn't he the same person who appeared under another name in several of the forums a couple of months ago, got widely discredited, and disappeared?
Scanning quickly through these posts now during a break in CP tests on a gas production rig it seems to me that a little knowledge can be a dangerous thing

 

[makingplansfor]

genuinely no connection from engine to the gearbox output shaft?

You are not measuring to the other side of a flexible coupling .... they have to be bridged in order to complete the circuit.

Just oil films on all the gearbox components ?

You may have to use a brush system such as MG Duffs "Electroeliminator"

Firstly, should I expect continuity from hull anode all the way to the prop?

In regard to the flexible coupling, I can confirm that it is bridged and I have good electrical continuity across it, so as you point out, anode to prop continuity via cogs and oil films (perhaps bearing casings??).

There is no sign of ever having an electro eliminator fitted and the 25 year old propellor is in pretty good condition for its age so presumably not much wrong except I guess for the amount of wear on the shaft anode which had lost most of its volume in a year.

I guess the answer to the question at the beginning of the post will confirm whether I should be looking at perhaps fitting a brush system from the gearbox to the shaft.

 

[vyv_cox]

On lifting out at the weekend, I was surprised to see that the main pear shaped anode had not eroded much and was covered in barnacles. The shaft anode had eroded as expected and was barnacle free. I have searched the forum for similar problems without success so looking for opinion. I suspect that the answer is about connectivity of the anode, however, from what to what etc. I guess that gives an indication of my knowledge on the subject!! Advice therefore appreciated.

I have read through the thread but I'm replying to your original question, bearing the rest in mind.

I see you have a Seastream 34, which I believe to be GRP, so forget anything you see about bubbling paint. You have none underwater except antifouling, which I doubt very much will be affected.

The question you need to answer for yourself is 'what is the hull anode connected to?' Many anodes have been retrofitted by owners believing that they are doing good, whereas in reality they are doing nothing, or possibly harm. Modern good practice is that underwater components such as seacocks, skin fittings, P-brackets etc that are inherently corrosion resistant should not be linked electrically or connected to anodes. If you have a raw-water cooled engine it should have an internal anode. Fresh water cooled engines will not be protected in any way by a hull anode, nor do they need such protection. Some heat exchangers have an internal anode, others do not need them.

On most GRP boats with a P-bracket and exposed shaft a shaft anode will protect a prop and shaft for at least one season, probably two. If your prop has its own anode so much the better, leave it there as well as the shaft anode. This is what I have. When I bought my boat it had a hull anode connected to various items. I took it all off 15 years ago, with no adverse effects.

If you have something more unusual, such as a steel rudder or another corroding underwater metal, you may need other measures. Otherwise a shaft anode and prop anode is all you need.

You can read from other respondents that the statements of coreng do not meet with universal agreement. His suggestions may well be true for large metal boats and structures but for small grp yachts they are inappropriate. I base this statement on the experience of thousands over very many years. In particular the photograph of the knocked down boat on his website is misleading and possible prosecutable.

 

[VicS]

Firstly, should I expect continuity from hull anode all the way to the prop?

In regard to the flexible coupling, I can confirm that it is bridged and I have good electrical continuity across it, so as you point out, anode to prop continuity via cogs and oil films (perhaps bearing casings??).

There is no sign of ever having an electro eliminator fitted and the 25 year old propellor is in pretty good condition for its age so presumably not much wrong except I guess for the amount of wear on the shaft anode which had lost most of its volume in a year.

I guess the answer to the question at the beginning of the post will confirm whether I should be looking at perhaps fitting a brush system from the gearbox to the shaft.

If the anode is to protect the prop there must be continuity all the way from the anode to the prop!
If that does not exist in your case then there is either a bad connection somewhere that you have missed or there is simply no continuity between the gearbox components. Poor continuity might be due to oil films but total lack of continuity is rather surprising.

It is difficult to know what to suggest without investigation.

The shaft anode will need regular replacement being so close to the, presumably, bronze prop but it will be giving you the protection you need, if indeed you actually need any protection of the prop.

Fitting an electroleliminator is something to consider if there is a good reason to do so.
You can see above Vyv Cox's beliefs and experiences.

The boat I have done most of my serious sailing on is a Westerly Berwick. It is now about 34 or 35 years old. It has no anodes at all. It still has the original prop and shaft!

 

[VicS]

Sorry to miss all the fun on this topic - I've been away at the annual NACE corrosion engineering conference in Houston
I don't think Coreng helps himself with his poor English but isn't he the same person who appeared under another name in several of the forums a couple of months ago, got widely discredited, and disappeared?
Scanning quickly through these posts now during a break in CP tests on a gas production rig it seems to me that a little knowledge can be a dangerous thing

You are thinking of several posts by "atyas" during January with links to the galvatest "white paper"

I wondered if atyas and coreng were one and the same. Decided probably not but would not be surprised to find a connection

 

[coreng]

Gentlemen,

I already said what I had to say (please excuse my poor english...). May I suggest you read the forum's rules again before posting and, finally, try to solve Makingplansfor problem, which remains largelly unsolved so far, despite your efforts to do so. After all, it's his post...

No use talking about me : my little case has no importance as I am right or I am wrong... And I have my knowledge, experience and convictions. Just as you...

By the way VyVCox, is your signature an attempt at SEO ?

 

[Tranona]

try to solve Makingplansfor problem, which remains largelly unsolved so far, despite your efforts to do so. After all, it's his post...

Not sure you are right there. His "problem" has been solved by a number of posts suggesting he does not need the "protection" that a hull mounted anode might provide. The vast majority of modern GRP boats simply don't need anodes other than to protect the prop and for most a prop anode or a shaft anode is perfectly adequate, particularly if the boat is on a swinging mooring or not connected to shore power. Sterndrives and saildrives are a different matter because of the mix of metals and in most cases they are fitted with generous anodes which perform well on a seasonal basis.

This is not dismissing the problem entirely because there are some situations where rapid anode depletion is a problem, but it is only in a tiny minority of boats.

 

[coreng]

Good. Let's go back to work and to constructive and friendly exchanges then.

 

[VicS]

My guess would be that the barnacles will only settle and grow on an anode if it is inactive.
I doubt if they would stay on a surface which is corroding away all the time.

Around an active anode the pH will be low(ish) and that may prevent them forming their shells.
Input from biologist required

However the first thing to do is check the bonding of the anode to whatever it is supposed to be protecting.

 

[bob26]

Is Zinc a barnacle aphrodisiac?

My guess would be that the barnacles will only settle and grow on an anode if it is inactive.
I doubt if they would stay on a surface which is corroding away all the time.

.

That may very well be so in this case Vic. But I have seen it suggested in several different places that cathodic protection (or maybe excess cp) can promote the accretion of barnacles on the protected part. And specifically that fitting shaft anodes, for instance, can increase barnacle growth on the prop. As I have both an active shaft anode and a fertile barnacle farm on my prop I'd be interested to hear if anyone can explain or verify any connection between cathodic protection and proliferation of the little shelly blighters.

From what I have read, they have a tendency to accumulate anyway. Apparently, once a free-swimming larval barnacle attaches itself with its own version of Sikaflex it releases a chemical substance which attracts other larvae to do the same nearby. They like to get together as, although the longest penis in the animal kingdom (relative to body size) lurks within those miniature Sydney Opera Houses, they are hermaphrodite so need to call on the help of a friend to reproduce. But what special magic anodes add to this love-in I have no idea.

 

[Tranona]

In my experience barnacles on the prop are location and time specific. I kept my boat on a swinging mooring in Poole Harbour for 3 or 4 years (on the same mooring). Had the prop completely covered one year (no anodes) but not the other years. Moved to a different swinging mooring in deeper water and strong tidal stream and no barnacles. Last 15 years or so in a marina with a hull anode no barnacles!

 

[coreng]

Thanks to you Bob26...

This is what I am trying to say since the beginning of this thread without any success. Once again - and I don't know why this message seems so difficult to hear - a high level of protection will possibly induce proliferation of barnacles. And this can be measured (on GRP boats, measures are taken on shaft from inside the boat).

Small extract from Nigel Warren's book "Metal Corrosion in Boats", probably the best available one : "Strong cathodic protection encourages calcium deposits and barnacles".

 

[vyv_cox]

By the way VyVCox, is your signature an attempt at SEO ?

Well, you've got me there! I don't have the faintest idea what you are talking about.

Vyv

 

[VicS]

SEO = search engine optimization

 

[coreng]

VyVCox, I asked you this because my signature (too explicit, as yours...) was charged upper in this thread... No matter...

 

[vyv_cox]

VyVCox, I asked you this because my signature (too explicit, as yours...) was charged upper in this thread... No matter...

No idea what you are talking about. My website is a free service to boat owners - I don't sell anything and give advice, if possible, to anyone who asks.

 

[coreng]

No matter.

 

[VicS]

Perhaps the following extract from the forum rules will explain why comments were made about the link to the galvatest website.

Special note on signatures and user pictures
a) Please place one hyperlink only in signature lines.
b) no direct links concerning boats for sale
c) commercial links are tacitly allowed in signatures only (they contravene forum rules but if you are subtle about it we will exercise a certain use of Nelson eye patch).
d) we ask for return links as a common courtesy - if you cannot link to http://www.ybw.com (or one or more of our magazine sites if you prefer) from your site then please leave the link off your signature.
e) the standards expected of the forum with regard to posting rules are the same for signatures, so please no abusive or obscene terms or links or graphics.​

Add a link to the YBW forums to the galvatest website and everybody should be happy.

 

[bob26]

This is what I am trying to say since the beginning of this thread ... a high level of protection will possibly induce proliferation of barnacles.

Small extract from Nigel Warren's book "Metal Corrosion in Boats", probably the best available one : "Strong cathodic protection encourages calcium deposits and barnacles".

Yes, I noted you and some others have said this.

Why does CP encourage barnacles?

Does it always - or just when metal is over protected?

 

[coreng]

I am not a biologist but I know electric fields causes minerals in seawater to precipitate and adhere to metal. This method is used to create artificial coral reefs. Difference of potential must be under -1000 mV which might occurs quite easily with cathodic protection, and always with over-protection.

But as Vics says, advice from an specialized biologist would be most welcome...