Sacrificial Anodes

[GordMay]

An excellent article on sacrificial anodes.

”It's No Sacrifice” ~ "Trade A Boat" magazine, Issue 339
Goto: http://boatpoint.ninemsn.com.au/port...2/Default.aspx
Preventive maintenance of immersed metals is a boating necessity. In the case of sacrificial anode replacement, procrastination is more than just the thief of time: it's the thief of your boat's integrity ...

[boredinthecity]

I think that this is going to be one of those, i wish i had not asked it questions, lol

SO if you have a copper sheathed boat' do you use an anode to protect it, and if so what metal is used in the anode

regards
Paul

[capt lar]

my guess is yes and zinc. i liked the part about folks painting the anode - seen it - gotta wonder.
capt. lar

[Sonosailor]

With all due respect, one should never guess when dealing with the nobility of metals. Check out GordMay's thread on the galvanic series, and do your best to understand it before putting metals together around salt water.

Whether or not zinc would provide better protection than magnesium requires an expert or personal experience. Area of protection per anode is also something that has to be dealt with.

Galvanic corrosion, crevice corrosion, erosion corrosion, edge corrosion, problems with corrosion byproducts, the interrelationships and solutions require deep understanding.

...and don't look at me for expertise; I only have confidence in what I don't know.

[capt lar]

properly corrected, but sometimes a best guess is all you have - over 50 years in my case. i look forward to reading what those with more science respond.

capt. lar

[capt lar]

properly corrected, but sometimes a best guess is all you have - over 50 years in my case. i do have some experience in copper sheathing and use of zinc without negative consequence, but relatively short term, and you make a good point that what seems fine initially may not have been the best choice. i look forward to reading what those with more knowledge respond.

capt. lar

[GordMay]

I presume we are talking about a Wood-Hulled boat, c/w copper sheathing?
If so, I’d refer you to some good information at:
USCG NVIC 7-95 - “Guidance on Inspection, Repair, and Maintenance
of Wooden Hulls”
http://www.uscg.mil/hq/g-m/nvic/7_95/n7-95.htm

I have seen references to increasing a Zinc anode by one size for copper-sheathed hulls (over a smilar FRG boat). This whole subject (wood, copper, zinc, etc) is very complicated, and I strongly suggest you consult a true Corrosion Expert.

Quoting Sonosailor, "... don't look at me for expertise; I only have confidence in what I don't know ..."

[Dman]

Of course I would of owned a copper nickel sheathed boat that had a steel hull.

[alaskadog]

Gord, Thanks for posting this article on anodes. I had long wondered about the usefulness of the "fish" anodes that I see some people use. I have seen them tossed over the stern of some boats when they were at anchor or tied up at the dock. I even had one man tell me that if you used them that they would prolong the life of prop and shaft zincs. I wasn't convinced so I never tried them. Apparently, they will work but only if firmly connected by wire to the metal they are supposed to protect. I don't think the article said what kind of wire one might use or how such a connection would be made. Do you have any thoughts on this? Or more specifically, how does one make effective use of those fish anodes? Thanks, Joe

[GordMay]

Joe:
"... how does one make effective use of those fish anodes? ..."

I don’t know - so don’t recommend them

A zinc anode must have a low-resistance electrical contact with the metal being protected. The conductivity of the water (between the hanging fish & the ‘precious’ metal) is inadequate, so actual mechanical contact is required.

"... what kind of wire one might use or how such a connection would be made ..."

If you coud effectively (see above) wire it, you could bolt it directly to the metal.

[Sonosailor]

They should work, and any wire that allows electrons to flow from the anode into the parent metal and make it a cathode should do the trick. I see their value when you want to protect your saildrive, prop, and the internal parts of your seawater coolant system from corrosion, and cannot see a good way to make a direct connection within the electrolyte (in the seawater). The limit on how well it works would be the distance between the anode and the cathode (saildrive or prop and shaft). Again, somebody smarter than me would have to provide the level of protection, for whatever distance between the two metals is possible.

However used, an anode will stop the lead from being leached out of your submerged brass and bronze metals (lead is the least noble metal in these alloys), and stop holidays in your aluminum saildrive paint system from growing into visible holes and aluminum pits.

I have eyed these rather expensive anode fish, but do not have good pathways for the wires, and do not like the idea of the wires rubbing along the sides of the hulls. Some through-hull bolts with wing-nuts would overcome some of that, but I also fear motoring about after forgetting about the buggers. I am going to focus on maintaining my internal engine anodes and my external paint, and try lanolin on the bronze to control marine growth and decrease surface area. Anode rings and anode prop hubs are also better than the fish if they are possible options.

WRT the article, it was nice to see that zinc is appropriate for salt water, and magnezium is better for fresh water. Thanks for posting it.

[Rick]

"Fish" anodes are only REALLY effective if there is a wire between the anode directly connected inside the boat to the prop shaft (via a proper shaft brush) or to the inside saildrive metal.

If one merely hangs a zinc anode over the side there is little reason to expect random movement of free zinc ions over to what you want to protect without a wire between the two.

Here's one method of wiring to the fish anode: buy some of that clear insulated insulated speaker wire (like you can get at Radio Shack). Peel it apart to get two wires to use. Crimp on terminals appropriate to whatever size fastener you put on the zinc using the more expensive terminals that have the thermoplastic sealer in the ends. You heat-shrink the terminal end on the insulation of the wire making a water-tight seal. Spray SP400 CRC industrial protectant ONLY on the terminal and fastener keeping the spray off of the rest of the zinc or else the zinc will not work...the SP400 will insulate it. As long as you don't physically wipe off the SP400 you will see that everything looks new after immersion in salt water. With the clear insulation you can observe that the internal copper wire remains uncontaminated and rest assured.

[Alan Wheeler]

I use a "Fish" anode. So far it works and I have not had any problem.
Normally anode would be bolted to the bottom of the rudder. I get ruffly 8 months fromt eh anode in the Marina. Because I can get two years out of the Anti-foul, it is an expensive excersise to haul just to replace the anode. So I decided to go the the "Fish" idea. I have a heavey cable of 16mm2 (sorry don't know what that is in Gauge). It is bolted to the rudder stock and hung over the aft so that the anode it's self is only a couple of feet from the steel rudder and prop. At the anode end, the cable is bolted through the galv strap that the Zinc is poured around. I have coated that with Lanocote and heatsrink over top of that. The cable connection has remained good. A good size cable is required so as little voltage/current loss is found in the cable. You want to have as an effective connection as you would have if the anode was bolted directly to the Rudder. The length of cable is such so as the anode or cable can not contact the prop when in reverse and when I am in motion, it just trails along in the water behind me. No Dramas.
The result is, I can pull the anose up anytime I want and inspect it and replace it if needed, and then drop it back over the side. The only negative is the cable gets slimey.

[alaskadog]

Thanks to all you guys (Gord, Rick, Sonosailer, Alan) for responding to my fish anode question. As usual, from this group of salts, I received some great input. As I kinda thought: Fish anodes can work but the proper connection must be made.Similar to Alan, I have shaft and prop anodes that must be replaced more often than haul outs for painting. As my bottom paint starts to lose its effectiveness over time, I find that I usually need to start scraping barnacles from the shaft and prop anyway cause that seems to be the first area to start losing paint in spite of how thoroughly I prep the metal prior to painting. I usually pay a SCUBA equipped diver to do the job and they will inspect and replace zincs on an as-needed basis. For my boat, it would likely be a bigger hassle than it would be worth to make a fish anode system work. Because I have been sitting in the marina more than sailing the past year, as expected, the barnacle problem has been worse and the more rapid deterioration of zincs has occurred. But now with a new bottom job and new zincs and looking to set sail for the Yucatan and points south in about two weeks I should be set for awhile. I hope to be on the hook most nights but I have definite plans to be in marinas for a bit. Just hope there aren't a big bunch of old stinkpotters in those places that are leaking all kinds of nasty stinkpot electrons into the water.
But I do have spare zincs. Cheers to ya