I know there is probably a thread on this subject but I can't seem to find it. We are hauling to replace zincs and give the bottom a once over.
We currently have two zincs on the shaft and I plan to add two 'rudder' (pancake) zincs to the strut since there is an existing hole.
Is this adequate? Overkill? ??? I understand that you can't really over zinc a fiberglass boat but that if you have too much they can become ineffective.
I appreciate any input. Thanks.
Actually, I would say you can not zink a fiberglass boat. The only things you can protect is the metallic running gear being the shaft, strut and prop. Seems like you have it all covered.
I would also advise you to replace the pencil zinks in your engine heat exchanger.
Dale
Since I can't tell how your boat and all your neighbors boats and you Marina is wired and protected, it's impossible to know how much cathodic protection you are going to need to keep your bronze strut and prop from burning off. In the meantime you definitely need to zinc up.
Beyond that the most important bit of info you need to keep track of is how long has at been since your zincs were replaced. Without dropping Silver/Silver Chloride reference electrode in the water and measuring the voltage to your underwater metal parts, the rate at which your zincs are burning is all you have to go on.
Here in Socal I have a diver that cleans my bottom once a month. On my boat which is attached to shore power that charges my batteries I go through 3 sets a zincs a year. I have a galvanic isolator which does not seem to help. I believe the problem is due to how manufacturers are required to follow NEC (national Electrical Code) which seems to be at odds with ABYC Electrical standards in regards to how they handle the neutral wire.
In my case I suspect that my marina has a problem with AC currents that overload the galvanic isolator and swamp the -1.1V galvanic potential of my Zinc. I plan to make some measurements to get to the bottom of this. Could be my dead beat neighbors who are all under zinced.
http://www.marinesurveyor.com/allport/zinc.html
I keep hearing about over-zincing from old timers. Here's an article that sheds some light on the topic. Its only a problem with wooden boats.
Pete
I doubt you can over zinc a boat. For instance, I added a pound of zinc powder to my bottom paint and covered the whole boat with it. Standard practice in then Caribbean, outlawed in the states.
Pete,
I saw a pic of the zinc on your strut on a previous post. I don't have that on Journey. Did you drill that up yourself? I will add one next haul out in January and was wondering what kinda bolt would be used to secure it without creating some kinda weird galvanic cell that would damage the strut.
Wayne
Wayne,
The idea of installing zinc anodes on your boat is to protect the metallic items that come into contact with the sea water. How it works is that each metal has a molecular structure that makes it less corrosive or more corrosive than the next. The more corrosive it is the less noble it is. Gold, silver and so on would be very noble metals, steel not so much.
When you have several different metals in the mix, the least noble of the lot corrodes or dissolves first. When it is gone the next least noble goes away and so on. Keeping this in mind, if you have a metal you are rather found of (your propeller for example) all you have to do is provide a less noble metal to be eaten instead of your propeller. This is why zincs are refereed to as sacrificial anodes. They are purposely installed as willing volunteers to protect the metals that you want to save. Think of out running a bear, you only have to be faster than the person next to you. In salt water the most common material for a sacrificial anode is zinc. In fresh water magnesium is preferred.
In order for this sacrificial process to work efficiently, the zinc must be in electrical contact with the more noble metal. This is why zincs are bolted or clamped on to their assigned metallic item that they are to protect. The fastener needs to be as noble or more noble than the actual zinc. The sacrificial anode must also be directly in contact with the water so do not apply bottom paint to the zinc.
As for adding powdered zinc to ones bottom paint and covering the entire submerged hull surface, if it was a steel or aluminum hull it might help. Covering a non-conductive fiberglass hull, not at all. I am curious of what is happening if your bottom paint contained copper, and what kind of a primordial mix you have concocted. I suspect by looking at the periodic table of elements, that because zinc is less noble than copper your bottom paint is now similar to Swiss cheese with voids where the zinc used to be. Are you sure you used zinc powder or tin? Tin is a far better sacrificial anode than zinc but indeed the government did outlaw the use of tin many years ago except in their own vessels.
Dale
At least in Grenada, the additive would be tin. You can still buy bottom paint with tin and small containers of additional tin to add to your paint if you wish.
But having said that, Wayne's gotten his "swiss cheese" bottom even farther than I've gotten mine.
All my best,
Dirk
Dirk,
Great to hear from you!
I would love to get my hands on some tin powder. I could buy cocaine here with out much of a problem but not tin powder.
Interlux makes a product called VC-17. It is a very slippery Teflon based product that has a bag of copper dust in the lid. You add the copper just prior to painting. Works well in fresh water and is unbelievably slippery, so much so that if you have a trailer sailor it is very difficult to keep the boat from moving around while under way on the trailer.
Dale
Dale,
Is this a product you might be able to stock/ship.
http://www.boatzincs.com/corrosion-reference-electrode-specs.html
This looks invaluable especially when your connected to shore power in a marina with derelicts all around.
Pete
Wayne,
I put the zinc on the strut because I wanted to ensure that it never experiences electrolysis. Its a very expensive thing to replace. It might be bigger than needed.
I've been doing some tests in a bucket of seawater with over zincing. Zinc has an EV of around -.7v. Bronze is running around +.2 v. Using a gold reference electrode I can impress a voltage onto the bronze. I think all you need to do is get your bronze slightly negative, say -.3 to .5 V for it to be protected. If you get it too negative -1.0 volts or more hydrogen bubbles begins to boil off you bronze. You are now plating you bronze with the sacrificial anode. Its also a battery that stores a charge. So I think Zinc works but the EV does not need to be that low. Its almost too much IMO, but it is what it is.
My idea is to use bronze as the sacrificial anode and to impress an external voltage on it (-.5 V). Worst case you end up electroplating your bronze with bronze. Platinum is too expensive for me.
Juries still out on these concepts.
Also I think the zinc and tin in the paint actually protects the paint, not the hull. Although in the early days of marine corrosion, they quit protecting the copper hulls because they found that unprotected it discouraged marine growth. When the added an iron sacrificial anode marine growth got out of control so they quit using it.
Pete
Dale,
My mistake, brain dead. It was tin that I added, not zinc, to the bottom paint. It has lasted well, but it will be time for a new bottom in New Zealand where it is also outlawed. *sigh* I shoulda bought extra and stowed it away when I was in Panama.
Pete,
I know a bit about the physics of what you describe. It seems to me it would not matter how much zinc you were putting on the bronze as the Delta-V would be the same. So is there a concern that the bigger the zinc, the bigger the current, therefore more plating? With a Delta-V that large, is a zinc even a good idea? Perhaps aluminum instead? Now I'm wondering about the reduction cells caused by Hydrogen ionization might cause brittling of the outer surface and lead to cyclic stress corrosion from prop vibration.
Just when I think I know something, then I find I still have questions. lol
Wayne
Wayne,
Undergrad chemistry wasn't my best class. But I found this white paper.
http://www.galvatest.com/WP_Cathodic_Protection.pdf
Aluminum would seem logical but there are problems with it. For a passive system in seawater its going to be zinc I'm afraid. Good discussion on over and under protection. On our polyester boats, over protected will as I guessed it burn the anti-fouling paint off (over -1.1 volts). On wooden boats your over protected at -.7V and it will destroy the wood fibers around through hulls. Explains the problem of being a wood boat in marina where everyone around you is over zinced. My friend with a wooden boat will not bond or ground anything on his hull for this reason. He'd rather have the metal fittings corrode than the wood fibers disintegrate.
I'm becoming a fan of active impressed corrosion protection systems. Other than the expensive platinum anode , the electronics are very simple and very low power. They can be dialed back from where you are with zinc.
Pete