Where to hang extra anodes

[MidlandsOnSea]

Last year I bought my Sealine with the outdrive legs showing signs of some corrosion. Inspection showed the Mercathode unit wasn't working, so got that replaced. However, I've read lots of posts with horror stories about bits wasting away plus posts about Mercathode systems and now I'm paranoid.

I understand one can gain extra protection by hanging some zincs over the side on a copper wire. My question is this: where exactly should I attach the ship-board end of the copper wire? One person suggested tying them round the mooring cleats on the pontoon.

Other info: I leeave the shore power connected all the time; I think I've got a galvanic isolator; boat can wait a month before it gets used.

Any suggestions?

 

[hlb]

I sometimes hang an anode off a stailess steel wire conected to my prop shafts. Guess you could just hang it off the engine Or your oudrive, err inside bit!!

 

[Coppershield]

Hi,
I would be very careful with extra anode!
For about 15 years I have been researching different aspects of marine industry; and I have found quite a few disturbing practices. I.e. marine retailers selling hang down extra zings, when I purchased one of these number of years back. I remember it did not come with any information.
During my research I have come across some information that clearly states, using more than necessary anodes on aluminum can cause aluminum to corrode. After this information , I paid more attention to the aluminum outdrives almost every case of severe corrosion was due to the fact owners thought they were getting extra protection by hanging extra zinc on the side.
I am not saying extra zinc should not be used, but it should be used with careful consideration given to the salinity of the water, temperature, surface coating and if there are any other additional components. That is in contact with the aluminum , but it is not part of the original design must be considered in this calculation. Especially if this components are stainless steel.
If I had a yacht with the outdrives, I will make sure it has either isolation transformer or galvanic isolator and a high-quality impressed current or regular anode system properly sized for the yacht in question.
I know I did not answer the question you asked I just wanted to share with you some of my findings involving extra anode's on outdrives.
If you are suspecting Your shore power to be the problem see if You can disconnected(physical disconnection of the shore power cord) and then make sure You have a galvanic isolator.
Discuss the idea of hanging extra zinc's with Your outdrives engineers they may be able to give You the proper size of zinc to use.
I hope this will be of help.
Good luck.
Muzaffer

PS when You call the company ask for the engineering department
don't discuss the matter with anyone(in the company) until You get to the engineering department on the way to this point if You give them Your name , and the company You work for. It usually helps(especially if the company name is not very descriptive.)

 

[stefan_r]

I have a hanging anode as installed by the manufaturer on my 46'er...it's connected to the grounding wire that connects to the engines>props>gearboxes>and all the other metal on board, it just connects with some copper wire off the other connections

 

[hlb]

I dont go along with this, it's just a case of making sure there still is some anode protection down there and easier than sending a diver down to find out.!!

Cant see how you can have to much.

 

[msimms]

Interesting comments, my assumption would be more is best. I've purchased, though not yet fitted extra anodes as the props suffered corrosion last year, mostly the small four blades but the larger three blade also suffered quite badly. I think the prop shop did a great job in repairing them!

As well as the standard fit zinc bar anodes and zinc duoprop ring anode I'm planning to fit a pair of small triangle zinc anodes to each leg and an additional round zinc anode to the upper side of the area above the props (not sure what that bit of the leg is called, exhaust, cavitation plate??). Both of these options I've seen fitted to the same (290) and similar legs around marinas.

I've also purchased additional round aluminium anodes to be transom mounted with stainless steel studs. Mixing the aluminium and zinc was my attempt at a belt and braces approach as I'm told there is a lot of fresh water in Chichester Marina.

I also made and fitted a galvanic isolator earlier in the year.

Do you have a copy of the information that states extra anodes causes corrosion that you could post? I'd be interested in reading it.

Cheers

Mark

 

[Ships_Cat]

Over-protection is said to cause disbonding of nearby paint systems on the protected metals (which include other metals on the boat not the target of the protection but protected by default). Disbonding would further increase the over protection due to the electrical resistance of the coating being reduced, so increasing the galvanic current further and accelerating the problem. The protection of the metal by the paint system would then be lost. I am unsure if it is actually a common problem as it is likely hard to diagnose against the symptoms of the other faults likely to be present in such poor installations - but see the later comments on the importance of the paint system on outdrives.

Good luck (sic) with all your anodes - remember, all you are doing is creating a short circuited battery and increasing the currents through your bonding system (or hull if that is metal). They may create their own problems especially at dissimilar metal interfaces, including on the drives. More is not better.

I work with large power boats (too large to have propped outdrives but commonly have aluminium bodied water jets drives which raise the same issues) and my suggestion is to actually find the cause of your problems not take the "lets throw some more sand in the blind man's eyes to see if that helps him see" type approach.

But it is very hard to diagnose a boat's galvanic problems from afar. However, I cringe when I walk around a marina and see all the power boats with outdrives with shore power permanently connected and I know that probably many of the boats (especially the smaller ones) do not have isolation from the shore AC earth - and they wonder why their anodes dissappear, to be shortly followed by their aluminium castings. But as is the often case on this forum, they are not interested in professional advice, just the scuttlebutt such as more anodes needed, it is the water, or it is the marina's or other boats problem.

It is commonly said on these forums that if the anodes are fizzing away then they are doing their job. Mostly it actually indicates an underlying problem which should be remedied. As a measure of this I recently did an underwater guarantee inspection for a fleet operator of some large new aluminium boats of high quality build with aluminium water jets (the jets had aluminium bodies and ss and bronze components) after their being in the water for around 2 months. The anodes on the water jets (only the manufacturer's anodes were fitted, and they should know best) were only just showing signs of minor pitting in a few areas and for the hull anodes (the boats being aluminium) it would be hard to tell if they were new or not as there was no visible erosion.

A very good article on the care of outdives is http://www.yachtsurvey.com/SternDrive.htm - it will be seen that he has views different to the "myths". He emphasises the importance of coating integrity and I agree with that in the case of aluminium castings, especially in the case of lesser quality alloys which may be used in pleasure equipment.

Coppershield is on the right track with his comments, regardless of the claims of some to the contrary. One thing is for sure, anyone who finds that it is necessary to add anodes or hang anodes off a boat, no matter what its construction, with bits of wire to "solve" a problem is just bandaiding the problem which is very likely to sometime expensively bite back.

John

 

[msimms]

Thanks for the post - certainly food for thought.