How many shaft anodes?

[bud37]

Mag anodes are very light, noticeably lighter than Aluminium.....zinc is obvious. If it was in brackish with no trips to salt they may have got away with magnesium but ????? ....anyway, mag anodes are the recommended choice for your location now.

You have the props off ....are you having them tuned ?...if so make a point to ask the prop people to inspect for any corrosion....I believe they would but not bad to ask.....why there were so many shaft anodes is puzzling.

[Viper]

Magnesium also ends up with deep crevices/pits when it gives up its mass.

I know the common thread is mag for fresh water and aluminum for salt and brackish but when you consider the metal potentials for what you have on inboard applications which is bronze and stainless steel, aluminum will work just fine in fresh water too. It'll still be way more active than the running gear, much cheaper than magnesium, and will last longer. I prefer not to use aluminum anodes on sterndrives and outboards because I prefer a wider potential between them and the aluminum casings they're supposed to protect which is accomplished with magnesium. The aluminum alloy of an anode is only just a little more active than that of aluminum casings but I feel safer with the more active magnesium for those applications. For inboards though, aluminum is fine.

[Carpediem]

There were three on the shafts on my 506 when we had it out for survey last month. I think the prior owner had an extra on for extra insurance as he was in a pretty hot marina in San Francisco Bay. I went with just two as I have the boat bottom cleaned and gear checked by a diver every quarter. I did some research and found that the anodes should equal 5% of the surface area that you are protecting.

[Midnightsun]

My boat was delivered with Zincs as are all boats from the factory even though Carver knew this boat was going to be landlocked in a fresh water lake. that being said after I took posssesion I noticed this and decided to replace the anodes with the proper material and went with Magnesium. The original zincs, shaft, transom and trim tabs were all zinc and did look almost like new when removed. The magnesium units on there now show some pitting after about 3 years but still are in excellent shape. I was seeing corrosion on the 4 underwater lights I made from aluminum attached to the trim tabs and the magnesium did help there quite a bit. If it were not for that issue I probably would have went aluminum all around or when it time again, aluminum everywhere except the trim tabs where I would still use magmesium. I am located in pristne fresh water all the time by the way.

One thing I did find odd though is the heat exchanger anodes are available only in zinc for the engines. Almost machined some out of aluminum but never got around to it.

[bud37]

There is a fair bit of science involved in anode choice and usage in different water types ( Salt, Brackish , Fresh etc ). I believe the correct course for most boaters is to follow the recommendations from the manufacturers of these important items as to what to use for their own specific situation.

One thing , don't mix metal ( anode ) types or you may create a battery and make matters worse.The anode metals are special designed alloys to provide protection.

This is in clean fresh water....When we bought our last boat, the surveyor showed me some very, very minor pitting on the props.....I cleaned them and inspected further.....well all the anodes were zinc and oxidized over, the bonding system connections needed cleaning and the chain was broken at one thru hull......fixed all and tested ok.

Fast forward to marina now......was still getting some small leakage numbers....tested all the cords around me with a clamp meter.....two of them were leaking, one more than 2 amps.... .....it calmed down after he moved....but all my anodes showed major consumption that year....props were fine now.....new anodes for next spring. I also approached the marina to do an anode education program after doing a survey of all the boats in storage.....most still had zinc anodes that looked almost pristine. Win ,Win....marina sells product and our boats are safer.

I moved marinas that year and when the boat was hauled the anodes showed almost no consumption at the new marina.That in itself is interesting as I had tested all the cords ( clamp meter ) around me in the new spot and all were good. I believe there is more good info out there now, more education is good but follow the science, I remember when all we could buy was zinc alloy anodes, how times have changed.

[Viper]

Source of the post.....I also approached the marina to do an anode education program after doing a survey of all the boats in storage.....most still had zinc anodes that looked almost pristine.....

Good point bud, it really is up to marinas and techs to educate their customers. Some are better at doing that than others. I keep saying the best customer is an educated one. The problem with your neighbours slacking off on proper anode maintenance is that it affects the anodes of surrounding boats. It makes your anodes give up more of their mass faster than they otherwise normally would. Doesn't hurt for boaters to bring up the subject to their neighbours either if they notice deficiencies with their anodes. In the end, if they're left uncorrected it will affect you.

[denpooch]

Viper you stated: "Ya too many anodes is definitely a problem as it will cause another set of issues that you don't want."
What other problems can occur? Thanks.

[Viper]

Some of the negative effects really depend on many conditions and are usually more pronounced on wooden and metal hulls but can have similar effects on some areas of fiberglass hull construction. I'm no expert in the effects but my recollection is that you can get burnback which is an effect you can see around thru-hull fittings where paint will be discoloured usually in a round pattern about a foot in diameter. This is a sign that the anitfouling paint in that area has been rendered useless. Paint delamination although more common on metal hulls due to too much anoditic protection but can also happen on fiberglass hulls around fittings as described above. I recall something about a chemical reaction causing a hydrogen fizz. Wood rot due to overprotection is most common on wooden hulls but there's always been talk about the possible effects on hull cores and backer plates around fittings. In reality under normal conditions it probably takes a fair amount of anodes to cause any of these effects but how do you know when you have too many or if your conditions are normal. The effects are also more commonly associated with impressed current anodic protection systems that might not be set up properly for a given application. Again too many variables to be an exact science but erring on the side of caution is best IMO and recognizing the symptoms helps.

[mjk1040]

Fresh water in NY I use aluminum, one on each shaft 4" ahead of the strut per the anodes company that sells just anodes and were very knowledgeable on everything anode. www.boatzincs.com

[V12diablo]

Thanks, mjk1040. Boatzincs is who I am going to use. I need to replace all the zincs prior to getting in the water.

Jason