Zincs

[KJ]

I was doing some routine maintenance today. Changed out the pencil zincs on the heat exchangers. Don’t know how long the old ones were in there (the PO didn’t keep records or notes). More than a year for sure. Zincs were gone. The tube bundle openings however, were surprisingly clean and open.
Picked up some spares with the new ones. KJ

 

[dhmeissner]

Wow! Good thing you checked them!

I have a related question. Recently my boat was moved from saltwater to a freshwater marina. We keep her on the Freemont cut east of the Ballard Locks in Seattle. We intend to do most of our boating in Puget Sound though. Question: should I change to magnesium "zincs"? Or doesn't it matter much? I suppose I could install both on the shaft and rudder, but the heat exchanger has only one zinc.

 

[FF]

Or doesn't it matter much?

I would be more concerned with how the energized water is if you keep her in a marina.

This can be measured.

 

[Codger2]

Question: should I change to magnesium "zincs"? Or doesn't it matter much?

I can't answer your question with any factual accuracy but if it were me I'd continue to use the zincs. What I can say, with assurance, is that I absolutely love the area you slip your boat in! Talk about "Boat Porn"! There's just about every type of water vessel known to man there.

 

[Steve]

Would there be a problem if dielectric grease were applied to the threads?
Steve W

 

[DavidM]

Magnesium "zincs" do a better job in fresh water.

Dielectric grease won't hurt anything and may make it a bit easier to tighten up and remove later.

David

 

[rwidman]

Would there be a problem if dielectric grease were applied to the threads?
Steve W

Since the anodes need to make electrical contact with the metal they are supposed to protect and since dielectric grease is an insulator, it's probably not the best choice.

Screwing the anode into place would probably scrape away enough of the grease to make electrical contact, but why chance it?

I think you would do better to install them with no lubricant.

 

[rwidman]

"Zincs" that are not made of zinc are not "zincs". They are "anodes". Anodes made of zinc are anodes as well.

 

[dhmeissner]

Thanks, I'm aware of that which is why I put the word zincs in "quotes", rather than say cathode.

 

[Tom.B]

Would there be a problem if dielectric grease were applied to the threads?
Steve W

I keep one of those little squeeze tubes (think: ketchup packet) of spark plug grease I pick up at the check-out counter at the local auto parts store in my toolbox for that very reason. Haven't had to buy a brass base for my pencil zinc in three years.

Tom-

 

[Shoalwaters]

Copper-based never-seize on the threads is a good idea. I have a set of tapered pipe-taps which are ideal for cleaning the hole in the brass plug and the hole in the heat exchanger. Clean the male threads on a rotary wire brush.

 

[psneeld]

From my understanding of dielectric grease and threads is it fills voids but doesn't prevent continuity between the threads and the threaded hole as the threads eventually make enough contact.

That said...most advice is no sealants, etc..

But always trying to "better" standard thinking...if you do a continuity check between the brass cap and the part you are trying to protect you should be OK...I forget what number of ohms it should be under but is probably available in searching the web. I just read 1 ohm as being max and should be as low as possible...hopefully less than 0.1 ohm.

 

[windmist]

Wow! Good thing you checked them!

I have a related question. Recently my boat was moved from saltwater to a freshwater marina. We keep her on the Freemont cut east of the Ballard Locks in Seattle. We intend to do most of our boating in Puget Sound though. Question: should I change to magnesium "zincs"? Or doesn't it matter much? I suppose I could install both on the shaft and rudder, but the heat exchanger has only one zinc.

I was just reading about this topic in the latest issue of Passagemaker (March 2013). Steve D'Antonio has an article about corrosion control and among the many items he wrote about, he suggested that using aluminum anodes are better than zinc in both fresh and salt water with aluminum having better electrical characteristics than zinc.

He also wrote that when zinc is exposed to fresh water it gets a coating on it that inhibits its usefulness when going back to salt water. I didn't know that and here in the PNW it is not uncommon for boats to have that scenario where they moor in fresh water and cruise in salt water.

The good news is when I was in the Fisheries store this morning I was told that aluminum anodes are about half the price of zinc anodes.


Ron

 

[dhmeissner]

Thanks Ron! Sounds like good advice in my situation to change from zinc to aluminum.

As for dielectric grease, since it is an insulator I would refrain from using it on threads, but I would use copper based grease instead.

 

[Chuck Gould]

Here's some additional information about aluminum, from the February issue of a local publication

digital.turn-page.com/i/106931/82

 

[dhmeissner]

Here's some additional information about aluminum, from the February issue of a local publication

digital.turn-page.com/i/106931/82

Thanks Chuck!

 

[rwidman]

I would probably change to aluminum anodes as I am up the river about 12 miles from the ocean but I still have a spare set of zinc anodes and during the year my diver changes anodes as necessary. I would have to find a way to make sure he used aluminum as well or I would end up with a mixed set.

 

[JAT]

The good news is when I was in the Fisheries store this morning I was told that aluminum anodes are about half the price of zinc anodes.


Ron

Ron, that's interesting... but I guess that might be the case depending on where you get your zincs...

I read an article yesterday that was linked by go2marine...and the zincs they were talking about were "Navalloy"....that only have about 5% zinc, the balance being primarily aluminum.... While they look interesting.... I did note that these zincs were the same price as the "all" zincs.....except on this site where I buy my zincs....

100% Zinc:
USAzincs.com :: Shaft Anodes-Barrel Collar :: ZINC for Salt Water Use :: X-7 SHAFT ZINC ANODE-CAMP CO. 1-1/2"

Navalloy zinc:
USAzincs.com :: Shaft Anodes-Barrel Collar :: ALUMINUM for All Water Types :: X-7 ALUMINUM SHAFT ANODE 1-1/2"

The navalloy zincs are reputed to last 30% longer or more than 100% zincs. It would be interesting to find out if they actually do...since it could effectively make them a little more cost effective....

 

[rwidman]

......... The navalloy zincs are reputed to last 30% longer or more than 100% zincs. It would be interesting to find out if they actually do...since it could effectively make them a little more cost effective....

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.

 

[Phil Fill]

Thanks Ron! Sounds like good advice in my situation to change from zinc to aluminum.

As for dielectric grease, since it is an insulator I would refrain from using it on threads, but I would use copper based grease instead.

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?


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. In fresh make sure your boat does not have any stray electricity as fresh does not conduct electricity very well so there is a higher change a person can get an electric shock in fresh water.

When we retire we might moor the boat back on fresh water. The reason we are moored in Everet, I hated the locks, and the water is brackish, first several feet are fresh and changes to salt about 4 ft. So with a 6 ft draft the majority of the boat sits in fresh water and its only the deep keel that gets growth. The only growth you will get in fresh water is green slime.

Anyway, I would not change to aluminum!

 

[Codger2]

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.

 

[Chuck Gould]

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.

 

[Codger2]

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.

 

[koliver]

KJ:
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.

 

[windmist]

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

 

[windmist]

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

 

[Phil Fill]

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.

 

[Chuck Gould]

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.

 

[windmist]

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.

 

[Art]

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!