# cathodic protection.



## amk (May 3, 2015)

Im sure it is not hard to figure out but is there a good place to get a zinc sacrificial anode and does anyone have any pictures of how they have theirs rigged up?


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## amk (May 3, 2015)

found this article on anodes https://www.martyranodes.com/content/martyr-resources/Aluminum%20Anodes.pdf
seems I need an aluminum anode to protect my aluminum boat... seems kind of funny to me


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## CedarRiverScooter (May 3, 2015)

I will only have my boat in (fresh) water for several hours at a time. Does it still need an anode? Where do you guys mount them & how?


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## PSG-1 (May 3, 2015)

amk said:


> found this article on anodes https://www.martyranodes.com/content/martyr-resources/Aluminum%20Anodes.pdf
> seems I need an aluminum anode to protect my aluminum boat... seems kind of funny to me



I agree, it does seem odd. From what I read, other materials are alloyed with the aluminum. I keep a boat in salt water year round. Found out that zinc anodes are not what they used to be. Apparently, due to more environmental regulations, they've started eliminating cadmium from the alloy with zinc....so, now, zinc anodes are not very effective. 

When I hauled my boat out in February, I found that my zinc was in perfect condition, and my center keel had rotted out:

https://www.youtube.com/watch?v=GvVoheTe0mw

After fixing the problem, and then painting with 5 coats of inter protect, and 2 coats of trilux 33, I installed a magnesium anode. It is dissolving quicker than the zinc, but at least that means it's working!


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## Johnny (May 3, 2015)

many of us have some very old Tin Boats that have never had and anode
and never had a problem.
I personally, have a 1959 14' V that has a few layers of paint on it. It has
been left in salty ocean water for up to 3 days at a time over the years with no problems.
Sure, of course, there are marine organisms that attach themselves to the hull.
but with proper routine cleaning once on the trailer, I have never had a problem.

If you only use your boat in fresh water and occasional brackish water, 
rinse it off when you get home, you should never have a corrosion or galvanic issue.

Now, if you have an UNpainted hull, and you leave your boat in salt water for days and days
or weeks and weeks and never maintain it, you are just asking for trouble.
If your hull has been "properly" painted with Zinc Chromate and the proper antifouling bottom paint,
then you are okay - BUT, you still must MAINTAIN your vessel. Wood, Fiberglass, Aluminum or Steel
MUST BE MAINTAINED to provide you the best of service.

In my opinion, in fresh or brackish water, the anode is a personal preference - 
if you want one, put it on. It is inexpensive.
My bass boat has a SteelFlex bottom and raw unpainted sides. I may put an anode
on each corner of the transom just because it looks cool, and, I do venture into salt
water with it from time to time.

Jus my dos centavos

psg-1: AWESOME boat !! AWESOME welding skills !!
Here in Florida, we have the 24 foot air boats that give tourists the thrill rides
in brackish water. I can only imagine how the hull looks when it is serviced every couple of years.
Great Video !!


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## amk (May 3, 2015)

psg- in the article it specifically says not to use magnesium on aluminum in saltwater it says its to reactive. Also it says your zinc anode can build up and oxide layer and stop working that maybe what happened. I'm not under any impression that im
an expert now but I've read a few articles on it and they all say magnesium anode on a aluminum hull in salt water = bad. just passing on what I read.


as for my application.
I frequently use my boat in the river which is freshwater but I do go into the salt water often my boat gets water in it around the pump and since I only have one drain plug some residual water remains in the boat almost all the time. I rinse it out so its probably mostly fresh but the aluminum from the build is 5052 and inside the boat it is not painted. I think an anode would help. If I just used it in fresh I wouldn't worry about it.


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## PSG-1 (May 3, 2015)

Thanks, barefoot johnny! I've been welding aluminum for the last 20 years, so, there's not too much you can throw at me that I can't handle. I've repaired a few keels like this.

Amk, I wouldn't say that using a magnesium anode in saltwater is necessarily "bad", as long as you remember to check it often, and replace as needed. If you look at the scale of anodic metals, you will see that magnesium is at the top, followed by aluminum, and then zinc.

Based on that, it makes sense to me to use magnesium anodes, even if it means replacing them a little more frequently. Anodes are cheaper than hulls, or expensive repair jobs.


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## amk (May 3, 2015)

the article just says the magnesium is over reactive with aluminum in saltwater and hurts the aluminum and causes hydrogen bubbles etc. More reactive isn't always better is what its telling me but I could be wrong I'd assume these guys know what they are talking about since the authors are engineers and ex navy nuc and licensed ABYC electricians.


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## PSG-1 (May 3, 2015)

I did some reading, and you're right....it is possible to 'overprotect' an aluminum boat by using magnesium anodes in salt water. Says the voltage difference can actually start lifting paint. :shock: Guess I should have studied into that before deciding to slap a Mg anode on my boat. #-o 

My boat has been back in the water for about 60 days. Perhaps I should haul it out ASAP, and check condition of the hull, and replace the anode with one made of aluminum, which is less reactive than magnesium, but more reactive than zinc.


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## Skiffing (May 6, 2015)

Here's how mine is mounted:







It's aluminum from boatzincs.com

Aside from the other benefits discussed above aluminum anodes are self cleaning - unlike zinc and magnesium which require metal [stainless preferably] brushing to reactivate if exposed to air.

Another good source of info is here:

https://www.performancemetals.com/anodes/navalloy.shtml


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## amk (May 6, 2015)

thanks that's good info.


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## smackdaddy53 (May 7, 2015)

Pure zinc is what you need, a hull can be under or over protected which are both bad. If it is not corroding away it is under protected and the hull is still the anode, if it is corroding away AND bubbling paint around the hull contact point it is over protected/drawing too much stray current through it. Large ships use electronics hooked up to their anodes to regulate voltage/protection depending on conditions so optimal protection is always in effect. An aluminum anode is useless on an aluminum hull because it is on the same level on the noble metals chart. You want something lower on the chart but not the least noble or you would be replacing anodes all the time. A good hull anode should wear away in about a year.


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## Skiffing (May 7, 2015)

SD - 

What material do you think engine manufacturers use for anodes on their aluminum engines?

Hint - it's not zinc.


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## amk (May 7, 2015)

The aluminum anodes are made different zinc requires brushing to stay active. If you actually read the article I linked in it may shed more light on why you can use aluminum. It sounds weird I know but there are 50 different types of aluminum these anodes are not 100% aluminum.


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## PSG-1 (May 8, 2015)

Well, after having used a Martyr Diver's Dream zinc anode on my Triton 1650, I can tell you that they don't work in salt water. Because the zinc was in like-new condition, and the center keel of my boat was history.

Then tried magnesium, but read about the potential of lifting paint....I went ahead and removed it the other day. The anode is pretty well shot after just 60 days in the water. I still won't know if the paint has been damaged until I haul my boat out for a closer inspection.

In any case, after trying these 2 types of anodes, I'm now switching to aluminum. If I don't get some satisfactory results here, I'm just going to buy a fiberglass boat and say the hell with it :x :x because I'm sick and tired of dealing with electrolysis.


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## Johnny (May 8, 2015)

oh, just remembered something from back in my Old Navy Days - - - 
while in dry dock, I was on one of the painting crews and we 
painted over the new, freshly installed anodes !!! (this is on a steel hull boat)
The Yard Commander came by and when he saw it he went bananas.
We had to remove ALL the paint with elbow grease, removers, etc.

so, if you install an anode on your watercraft, *DO NOT PAINT IT* !!!


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## Skiffing (May 8, 2015)

PSG-1 said:


> Well, after having used a Martyr Diver's Dream zinc anode on my Triton 1650, I can tell you that they don't work in salt water. Because the zinc was in like-new condition, and the center keel of my boat was history.
> 
> Then tried magnesium, but read about the potential of lifting paint....I went ahead and removed it the other day. The anode is pretty well shot after just 60 days in the water. I still won't know if the paint has been damaged until I haul my boat out for a closer inspection.
> 
> In any case, after trying these 2 types of anodes, I'm now switching to aluminum. If I don't get some satisfactory results here, I'm just going to buy a fiberglass boat and say the hell with it :x :x because I'm sick and tired of dealing with electrolysis.



Are you docked anywhere near where other boats are using shore power? If so - that's the problem 

Do you have any negative electrical connected to the hull [other than the engine being mounted]? If not, are the engine anodes all in good shape?

If you look at the cart in the link I posted above you will see that the voltage differential between aluminum and ziinc is 0.30 volts. The differential between aluminum and aluminum anode is 0.35. That means it provides better protection than zinc in addition to being self cleaning.


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## PSG-1 (May 8, 2015)

No shore power that I'm aware of. Only my neighbor's dock, and he has a small 14 ft fiberglass boat. No negative wires grounded to the hull. Engine anode in good shape, and definitely no paint on the anodes!

I'm hoping the aluminum anodes will give me better results. Ordered them a couple of days ago, they should be here soon.


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## Skiffing (May 10, 2015)

Maybe dock lights? Sometimes wired with "funky" splices that can leak...........

Good luck


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## PSG-1 (May 10, 2015)

Skiffing said:


> Maybe dock lights? Sometimes wired with "funky" splices that can leak...........
> 
> Good luck




He does have a light on his dock, along with a receptacle. I would think the electrician would have installed the wires through conduit, etc. But then again, it was done sometime shortly after Hurricane Hugo in 1989, so, maybe it warrants some investigation. Think I'll talk to him and we'll take a look at the run of wires, the receptacle, make sure everything looks OK. If not, I'll offer to help him get it fixed. Because if this is the culprit eating up my boat, surely it has to be doing some damage to the portion of his motor that's in the water, since it's right next to the source.


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## Skiffing (May 10, 2015)

Check the polarity too. That's easy to check and easy to mess up on. If the cross is somewhere in the house before the docks lights branch out the electrician may not have even checked it - or cared.

There's an easy way to check potential across common / ground to earth [the water at the dock] but I can't remember for sure how to do it.


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## PSG-1 (May 11, 2015)

Thanks for the info! I think there's a tester you can plug in to a receptacle to tell whether polarity has been reversed. 
My anodes will be here tomorrow, so I can go ahead and get the galvanic protection back on the boat.


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