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Old 02-20-2013, 10:39 AM   #21
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I don't know how we figure that out, but I don't want to save money on anodes only to see my prop eaten away.
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Old 02-20-2013, 11:49 AM   #22
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We where moored at the very south end of lake union for 11 years, going back and forth between the fresh and salt , Zincs lasted 3 to 5 years. In Everett brackish they last 3 years if lucky.


About the only reason I can figure that any sort of anode would last 3-5 years on Lake Union would be that the zinc was covered with freshwater slime that prevented the anode from doing its job. Galvanic corrosion was still occurring someplace, you can be sure of that. Something else was being sacrificed to permit a 5-year lifespan for your zincs.

Zinc is really good in saltwater, not so good in fresh because of slime buildup. Magnesium works fabulously in fresh water, but is so "hot" that it almost dissolves in salt. Aluminum will be the dominant choice in the future for marine anodes, and it works very well in saltwater and is less susceptible to slime-over "insulation" in fresh.
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Old 02-20-2013, 01:03 PM   #23
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Galvanic corrosion was still occurring someplace, you can be sure of that. Something else was being sacrificed to permit a 5-year lifespan for your zincs.
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Old 02-20-2013, 01:03 PM   #24
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In my experience, the pencil zincs last about 1/2 as long as the hull zincs. They often break off before they are used up, so if you can get the end cap of the Heat Exchanger off, you will find lumps of zinc laying there. Good to get that area cleared out every once in a while.
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Old 02-20-2013, 02:00 PM   #25
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I would not change to aluminum if the boat is moored in fresh water most of the time. Galvanic rating of zinc is 3 and aluminum is 7. Might be Ok to change to aluminum if the boat was in salt and the zincs where going to fast. Why would you want to go to a high galvanic rating if the zincs are lasting and working?
The article that Steve D'Antonio wrote in the March, 2013 issue of Passagemaker about corrison control said that aluminum anodes have a "relative energy capacity" of 1108Ah per lb. with a voltage of 1100 millivolts versus zinc which has a "relative energy capacity" of 368 Ah per lb. with a voltage of 1050 millivolts. Don't ask me what that means except it is what makes aluminum better.

Steve also says in the article, "Zinc anodes are less effective in fresh water or brackish water, and they pack less of a protective punch in any water when compared to other alloys."

He also wrote that 2 manufacturers of anodes, Performance Metals and Martyr, didn't understand why people would use zinc rather than aluminum for protection.

Based on what D'Antonio says, I may have shoot myself in the foot. I recently added a fresh water rinse to my engine cooling system so now I wonder if when I fill the salt water passages in my engine with fresh water, am I losing my zinc anode protection because the 3 pencil zincs are getting a calcareous coating making them ineffective? I will probably pull one out and see what it looks like.

Someone else mentioned they didn't find that the price of aluminum anodes was less than zinc. My only information on that statement was what the Fisheries floor salesman told me. I checked Boatzincs.com and they did charged more for aluminum anodes than zinc anodes.

Ron
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Old 02-20-2013, 03:54 PM   #26
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MORE INFORMATION

I checked the price of a 2 inch shaft anode at Fisheries Supply and found that the aluminum anode was about $1.50 cheaper than a zinc anode so I was given faulty information that I passed on. Sorry.

Concerning using aluminum versus zinc anodes, this link covers the subject thoroughly:


http://www.martyranodes.com/content/martyr-resources/Aluminum%20Anodes.pdf
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Old 02-20-2013, 05:46 PM   #27
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Are you still moored on Lake Union? So how long do your zincs last in fresh water?

Maybe I/we should be more clear which zincs are we talking about?

Twice a year I have a diver clean/check the zincs and hull. The main big diver dream zincs last 3 to 5 years. However the small clam shell bow thruster zincs and engine pencil zincs where changed every year. I had a big divers dream zinc installed to replace the small bow thruster clam zincs so they are lasting 3 years also and the engine pencil are lasting longer also.


Thanks for the article. He is talking about a SPECIFIC aluminum, Indium Alloy, not regular general aluminum. According to the article Indium Alloy which sounds like an aluminum magnesium combined alloy. The galvanic table I have shows Indium has a high rating then zinc, so according to my table it would not protect it as well? So if you are going to switch make dam sure its aluminum Indium Alloy, that has a low galvanic rating then zinc and not some other aluminum alloy. Anyway it does not beat zinc by much, and not worth the risk. The article can be misleading if you to not understand the specifics.


If you wold like a copy of the galvanic rating military MIL-STD-899 table send me you email adress. Very important to know the galvanic rating of different metals.

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Old 02-20-2013, 06:10 PM   #28
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Hello, Phil

I moor at Queen City Yacht Club on Portage Bay, (for anybody not familiar with it, it is fresh- located between Lake Union and Lake Washington in Seattle).

I get about 18 months out of a hull zinc, and that seems to be typical of results experienced by neighboring boaters. I am going to switch to aluminum next time I change zincs. Most of my actual boating is done in salt water, but the boat (alas) spends a lot more days every year in her freshwater slip than out cruising. Zinc seems to have a very slight edge over aluminum in salt while aluminum seems to have a clear edge over zinc in fresh. Galvanic corrosion is a matter of time elapsed, not miles traveled, so beefing up the freshwater protection (without sacrificing the salt) makes sense in my case- as well as for many other boaters who moor in fresh but do most boating in salt.

I've always heard that it's best to replace a zinc when it has eroded to about 50% of its original size. Something to do with a relationship of the surface area of the anode to the items being protected.
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Old 02-20-2013, 08:54 PM   #29
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Phil wrote:
Are you still moored on Lake Union? So how long do your zincs last in fresh water?

No, I moor at the Port Orchard Yacht Club which is all salt water. I might take a trip once a year to Lake Union and/or Lake Washington. I was just trying to help people like you who moor in brackish or fresh water where the "experts" say use aluminum anodes.

The technical aspects of this are way over my pay grade so I rely on the "experts" and I think Steve D'Antonio knows more than I do. Also the Martyanodes.com web site, a major anode manufacturer, seems to recommend aluminum anodes over zinc for my situation based on their technical papers.

I have the boat checked twice a year by a diver, as you do, and I usually have to change the shaft zinc every 6 months and the rest of them once a year. I would make the switch to aluminum anodes if I could make a 100% switch but at this time my Sidepower anodes only come in zinc so I will stay with zinc for now. However I would sure be willing to go to aluminum if I could.
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Old 02-22-2013, 01:22 AM   #30
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I use zinc as anodes for my boat’s cathode protection in all types of water. Since leaving SF Bay’s salt water I’ve been year round keeping our Tolly far into SF Delta’s completely fresh water. Our covered dock is on side of a Non Hot well flushing channel. I make sure the boat is always left as an “island” from the dock by off hooking dock power and having only tie-lines in contact with the dock. I also isolate all batteries so no stray DC current travels to or through boat’s metal portions. With a boat in any water (fresh lesser than salt) the hotter that the area is (more stray 120V electric current in the water) the faster the anode of any composition will disintegrate. Zinc in freshwater will become coated on its surface (by oxidation and live growths) over a period of from 4 to 7 months. If let to continue this coating will eventually reduce the zinc’s effectiveness and could negate it. BUT – as long as every 4 to 6 months all the zinc surfaces are well scrubbed clean with bronze brush and/or metal scrapper edge (BBQ brush/scraper works well) to fully remove the coating and again reveal pure zinc surfaces the zinc will continue to function perfectly as anode that protects the boat’s cathodes. Where we keep our Tolly the fresh water is swimmable from mid April through mid October. I’m very careful to keep zinc surfaces well cleaned by swimming under with fins, mask, flashlight, brish/scraper. I swim often... Zinc works well for me!
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Old 02-22-2013, 07:42 AM   #31
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Every marina or environment will be different. Squalicum in Bellingham is a "hot" marina and the average service life of the typical "license plate" zinc is about six to eight months. The marina often has a layer of fresh water on top due to nearby streams and the river that empties into the bay. So many boaters including us hang a zinc on a heavy cable down about six or eight feet off the boat. The other end of the cable is attached to the boat's bonding system.

We and the boaters I know (and boats I see hauled out) never have any slime or algae on the zincs. I was told by people in the business ess that this is because the tiny current in the anode prevents growth from occuring. If there is slime or growth on an anode, it means the anode is not doing a very good job for some reason.

People have tried aluminum anodes in our marina and in every case I have been aware of they soon went back to zinc as they found the aluminum was not providing as effective a level of protection as the zinc does. But this probably varies wiith the environment the boat Is in.
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Old 02-22-2013, 10:59 AM   #32
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Every marina or environment will be different. Squalicum in Bellingham is a "hot" marina and the average service life of the typical "license plate" zinc is about six to eight months. The marina often has a layer of fresh water on top due to nearby streams and the river that empties into the bay. So many boaters including us hang a zinc on a heavy cable down about six or eight feet off the boat. The other end of the cable is attached to the boat's bonding system.

We and the boaters I know (and boats I see hauled out) never have any slime or algae on the zincs. I was told by people in the business ess that this is because the tiny current in the anode prevents growth from occuring. If there is slime or growth on an anode, it means the anode is not doing a very good job for some reason.

People have tried aluminum anodes in our marina and in every case I have been aware of they soon went back to zinc as they found the aluminum was not providing as effective a level of protection as the zinc does. But this probably varies wiith the environment the boat Is in.
Marin

See bold areas in your quote above. Reason you get no coating on your zinc is due to your "hot" marina area and being primarily in salt water. Your zinc's surface is disintegrating ("flaking off") so quickly, (in its correctly functioning less noble anode mode) that coatings get no chance to form. Where as in our "not hot" fresh water docking area the zinc surface stays on so much longer that surface coating can form. I've never seen surface coating form on zinc in water that is fully or majority salt due to its considerably increased electric conductivity as compared to pure fresh water. I'm glad to hear zinc keeps your boat's cathode metals free from electric current ruin!

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Old 02-22-2013, 04:09 PM   #33
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If you had a galvanic table it would be clearer. Metal mfg companies for centuries have used the galvanic table. The lower rate metal will protect the high rated metals, and the larger the spread the better the protection. Sure their might be an aluminum magnesium that has a little lower galvanic rating then zinc, but on the table magnesium is the lowest.

If the zincs are lasting to long then magnesium, which has the lowest galvanic rating should be used. If the zincs where not lasting long enough there are two choices. 1) added a additional/bigger zinc and/or 2) change to aluminum with a HIGHER galvanic rating which would still protect the metal with higher galvanic rating. When we moved to Everett, brackish, the bow thrust zincs where not lasting, so I hung a grouper zinc over the side which help prolong the thruster zincs and additional protection. When we pulled I had a big diver dream, license plate size, installed for the bow thruster.


Lastly if you are still unsure, then ask the boats around you what they use and how long they are lasting.
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Old 02-22-2013, 04:42 PM   #34
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Only if they are still protecting your underwater metal.

I don't know how we figure that out, but I don't want to save money on anodes only to see my prop eaten away.
I am in complete agreement with you.....

It will cost me far far less to buy zincs than to buy two new nibral props....

I should ask my diver if he knows anything about these new navalloy zincs.
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Old 02-22-2013, 04:45 PM   #35
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I am in complete agreement with you.....

It will cost me far far less to buy zincs than to buy two new nibral props....

I should ask my diver if he knows anything about these new navalloy zincs.
I'll ask mine also but not until I've used up what I have.

I'm sure he's putting on zinc when he replaces them so if I were to change to aluminum, I would have to make sure he used aluminum, not zinc when he replaced them.
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Old 02-23-2013, 03:54 PM   #36
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I would check the pencil zinc lenght before installing. I have to cut off 3/4 inch on my Lehman 135 SP to prevent binding at the center of the heat exchanger end cap. Same on my genset.
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Old 02-24-2013, 12:43 PM   #37
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I would check the pencil zinc lenght before installing. I have to cut off 3/4 inch on my Lehman 135 SP to prevent binding at the center of the heat exchanger end cap. Same on my genset.
Ditto.... I have to custom cut the zincs that fit in my stainless MESA wet manifolds!! Small chore...but a full length one won't fit.

Hmmmmm, maybe I should see if I can find shorter ones to use....
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Old 02-24-2013, 02:54 PM   #38
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Hmmmmm, maybe I should see if I can find shorter ones to use....
I was going to suggest that.
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Old 02-24-2013, 04:35 PM   #39
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You shouldn't have to cut zincs for the Lehman 135. There are shorter ones.
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Old 02-24-2013, 05:02 PM   #40
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I was going to suggest that.
In truth...I have been using up the supply of the extras that the PO left with the boat when we boat her..... I'm getting to the end of that supply.....
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