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Zinc Or Aluminum Anodes On Mid Chessie

As I was about to order a prop anode for our boat I saw 3 choices, zinc, aluminum and magneseum. I know mag is strictly fresh, I've always used zinc and never gave it a second thought but in reading up on it I see aluminum alloy is recomended for brackish water which is what the mid Chessie is. Now I'm thinking on ordering the prop anode in aluminum as well as replacing the shaft zincs with aluminum as well. So now it's time to dip into the wealth of knowledge here and ask for input and experience. Any thoughts?

I too have always used zincs but would be interested in knowing if any mid and upper bay boaters use aluminum? Would there be any issue trying one zinc and one aluminum anode on a SS shaft?

Re: Zinc Or Aluminum Anodes On Mid Chessie

Quote:

Originally Posted by T37Chef (Post 999128)

I too have always used zincs but would be interested in knowing if any mid and upper bay boaters use aluminum? Would there be any issue trying one zinc and one aluminum anode on a SS shaft?

BoatUS – BoatTech – Sacrificial Zincs by Don Casey

Quote:

In recent years cadmium in zinc has become an environmental concern, leading to a movement in the direction of aluminum anodes. Such anodes are effective even for protecting aluminum components--lower end cases, for example--because the aluminum used in the anode is a more anodic alloy. Aluminum alloy anodes are almost certainly to become more common. It has not happened already only because the cost of aluminum anodes has been higher than zinc without any discernable benefit to the boatowner. Today aluminum is actually cheaper than zinc. In addition, aluminum anodes tend to last longer, they work better than zinc in brackish water (and maybe in salt water as well) and they appear to be better for the environment. When making the switch from zinc to aluminum, ALL of your anodes must be aluminum. This can be a problem in some locales as many local marine suppliers still do not stock a wide selection of aluminum anodes. That will eventually change.

In fresh water, magnesium anodes protect underwater metals better, particularly underwater aluminum. However, magnesium is a good choice for freshwater only. If any of your boating is also in brackish or salt water, fit aluminum anodes

.

Wikapedia

Quote:

Aluminium anodes have several advantages, such as a lighter weight, and much higher capacity than zinc. However, their electrochemical behavior is not considered as reliable as zinc, and greater care must be taken in how they are used. Aluminium anodes will passivate where chloride concentration is below 1,446 parts per million.[11]

One disadvantage of aluminium is that if it strikes a rusty surface, a large thermite spark may be generated, therefore its use is restricted in tanks where there may be explosive atmospheres and there is a risk of the anode falling.[8]

Since the operation of a galvanic anode relies on the difference in electropotential between the anode and the cathode, practically any metal can be used to protect some other, providing there is a sufficient difference in potential. For example, iron anodes can be used to protect copper.[12]

The rule is not to use different materials for annodes on the boat. Some of the Yanmars even have sacrificial zincs in them so I would be careful of crossing over to another material.

Lastly the purpose of the zinc would be defeated at its supposed to be a different noble matel, thus attracting the current and sacrificing its self. We dont have any allumininum in the water that I know of its all stanless steel like the shaft. but in the case some one would like a PB or a swim ladder, or even the prop of an outboard dinghy or whatever it would make it ineffective.

I am staying with traditional zinc.

Re: Zinc Or Aluminum Anodes On Mid Chessie

I think you'll find your favorite zinc anodes more available at your favorite chandeliers then Aluminum ones no matter where on the Chessie. Zinc is more readily found and easier to produce..

Re: Zinc Or Aluminum Anodes On Mid Chessie

OK, I believe I have it down. On the Chesapeake from the head to just North of Baltimore is considered "fresh". Then there are 3 stages of brackish below that point. It is Oligohine where the salinity is .5 to 10 ppt (parts per thousand) is from north of Baltimore to the Bay Bridge. It is Mesohaline (salinity 10.7-18.0ppt) from the Bay Bridge to the Rappanannock (medium salinity). It is Polyhaline (18.7-36ppt) from the Rappohannock to the ocean (36ppt is ocean water). So if Aluminum alloy anodes are made for brackish water the Chesapeake is definitely the place to use them. Also, I read a zinc anode can form a layer of zinc oxide insulating itself, then the protected metal will deteriorate. So upon reading this I've ordered all aluminum alloy anodes (Non Chinese) and will put on our boat. I've used zinc my whole boating history on the bay, I wonder how much easier some of those outdrive and lower unit tear downs would have went if they were protected with Aluminum alloy anodes. BTW its aluminum ALLOY so this anode is less noble than straight aluminum.

This is a change of thinking and might seem strange but I remember seeing that first computer at work and thinking "Yeah, that'll be out of here soon".

Re: Zinc Or Aluminum Anodes On Mid Chessie

Quote:

Originally Posted by swampcreek (Post 999367)

Why fix what ain't broke?

If you don't have any evidence of galvanic corrosion, using cheap and commonly available zinc anodes, why change?

Re: Zinc Or Aluminum Anodes On Mid Chessie

Quote:

Originally Posted by PalmettoSailor (Post 999723)

Why fix what ain't broke?

If you don't have any evidence of galvanic corrosion, using cheap and commonly available zinc anodes, why change?

FYI- aluminum anodes tend to be less expensive than zinc.

Re: Zinc Or Aluminum Anodes On Mid Chessie

Quote:

Originally Posted by PalmettoSailor (Post 999723)

Why fix what ain't broke?

If you don't have any evidence of galvanic corrosion, using cheap and commonly available zinc anodes, why change?

We may very well have this boat a long time, I just want to do whats best for it. Nowhere do I read any technical articles that zinc is better in brackish water, I read just the opposite, the only promotion of zinc over aluminum are the arguments like "that's what we always have done". I've heard of different anodes before but never concerned myself with them but our present boat cost more than all my previous boats combined. I've had some real adventures trying to disassemble old outdrives and lower units, I wonder how much easier some of those jobs might have been if they were protected with aluminum alloy.

To put it another way many cars were produced without oil filters way back when, those kind of caught on too.

Re: Zinc Or Aluminum Anodes On Mid Chessie

Quote:

Originally Posted by swampcreek (Post 999755)

I have kept zincs on my boats for many years and never had a problem with galvanic corrosian.

However sacrificial anodes of any matierial zinc or aluminum are not as effective as a galvanic isolator, As the anode deteriorates it loses it abilities. The isolator hhoks in with the shorepower cureent where a lot of the problems may occur.

http://www.defender.com/product.jsp?...12796&id=52807
If you really are truly serious and concerned with protecting your expensive purchase buy a galvanic isolator. It will protect you boat much better. I would still use a sacrificial anode.

Quote:

Sacrificial zincs corrode away as they protect metal thru hulls, shafts and props from damaging electrolysis. Stray, low voltage current flowing between the AC safety ground and DC bonding system is a principal cause of this "galvanic" action. This type of stray current will normally overload your zinc anodes as they try to protect other near by boats and/or metal objects of the marina.

Quote:

Marine Galvanic Isolation
A luxury yacht or commercial vessel is an important asset worthy of the best corrosion and safety grounding protection available. While protective coatings and anodes can help protect your boat, a sure method is required to deal with the galvanic corrosion circuit created by the shore power connection. The DEI Galvanic Isolator surpasses all other galvanic isolator electrical ratings.

The Solution:

A simple method which virtually eliminates this galvanic corrosion problem is to insert an appropriately rated and certified fail-safe Galvanic Isolator in series with the grounding conductor of the ship-to-shore power cable. The function of the Galvanic Isolator is to provide AC continuity of the grounding conductor (required for safety in the event of an AC fault) and to block the flow of corrosion-causing galvanic current.