Corrosion on anode

[OceanTrvlr]

I know my anodes are supposed to be sacrificial and all but, I haven't seen them look like this before.

Is this just funny looking corrosion or something else?

Ethan
2018 North River Boats Almar RAIV

Photo Dec 12, 1 14 14 PM.jpg (141.24 KiB) Viewed 10622 times

Photo Dec 12, 1 14 19 PM.jpg (130.77 KiB) Viewed 10622 times

[Chaps]

Well it certainly needs to be removed and cleaned (acid dipped or sand blasted) to see its true condition and to evaluate why it is not performing properly. If it is zinc (and it looks like it probably is) toss it and replace it with an aluminum anode. Is the outboard anode wasting away kind of rapidly and needing frequent replacement? That would indicate that it is trying to protect the whole boat (engine and hull are all one big chunk of metal in this case) and the growth encrusted hull anode isn't doing anything because zinc anodes are less galvanically reactive than aluminum anodes and when both types are attached to the same aluminum boat the zinc anodes will let their enthusiastic aluminum buddies on the engine perform all the corrosion prevention duties even for the hull while they sit back and collect barnacles.

[OceanTrvlr]

Thanks for commenting.

The anode is aluminum (1/2" 6x12 plate I cut in half and drilled for mounting), and I think it's working wonderfully. Yes, it's protecting the whole boat, as I think intended by North River Boats. I replace the anode twice a year and it seems to be moderately active. The engine's anodes also appear to be active but seem well balanced electrically with this large hull anode.

But, I haven't seen it have this "mushroomy" surface appearance before. I'll just file it away in the "strange-activity-on-anode" category and move on. New plates will go on before the boat is re-launched (along with a good powerwashing).

Here's the boat, by the way:

yellowfin_3156.JPG (99.65 KiB) Viewed 10517 times

[kmorin]

OceanTrvlr,

The anode is aluminum (1/2" 6x12 plate I cut in half and drilled for mounting), and I think it's working wonderfully.

Is the plate an aluminum anode alloy? Or is it just a piece of 6061 or 50series? Just curious, surface action is odd looking for sure. I think the actual anode alloys aren't intended to be as corrosion resistant- they'd be engineered to be less noble than the 50 or 60 series? At least as far as I'm aware?

Just curious from the wording in your post?

Cheers,
Kevin Morin
Kenai, AK

[Chaps]

Agree with Kevin, typical flat stock won’t be reactive enough to work properly. Get 6x6 alum anode plates from boatzincs.com just drill holes they have the right alloy specs and won’t get that growth

[gandrfab]

photobucket got cocky and is not our friend anymore.

[OceanTrvlr]

Good question. I had to go back and check.

The anode in my photos is a 6x12 hull anode (A-24779 alloy?) which I purchased from BoatZincs.com and cut in half.

[Chaps]

That's the right anode, looks like it lost its connection to the hull. Clean it to bright metal, clean the mount hardware & clean the mount location. Make sure everything is tight when you put it back on.

[kmorin]

I'm not currently conversant with all the many product offerings of anodic materials or finished assemblies so my remarks will probably ignore some or another solution to this problem?

There are two general products; one bolted or otherwise mechanically fastened to the hull and the other welded in some or another scheme - to the hull. The bolted products rely on one method of creating a path of very small resistance, the welded usually have cast in welding coupons - which usually result in a much lower resistance between the hull and anode.

In the first general class, the anodic material has an interface boundary that is subject to changes in resistance. IF V=IR and the R goes way up ?? .... that kind of implies the other values shift; this results in some installations where there is effectively NO anodic protection because the interface of the anode to hull has more resistance than other parts of the hull to the water. Stray current for whatever reason will take the path of least resistance- bypassing the anodes, sacrificing the hull or appendages.

I don't know if this is the case in the photos shown?

The other product class has an aluminum alloy bar/strap/band cast into the anode and those bands' ends are welded to some part of the hull. Some will install a surface mounted plate (welded continuously) over the hull material to weld this replacement anode too? Other's will weld directly to the hull- what separates the two classes of products is each designs susceptibility to resistance change at the electrical connection to the hull and therefore a shift, over time, of anode's potential from any charge on the hull- to the water.

Bolting 'zinc's' to the hull is just not going to result in the lowest resistance connections to the hull. Welded connections aren't always as easy to find or attach but they do (electrically/galvanically/physically) perform longer term more reliable (read: lowere resistance) connections to the hull since they don't rely on multiple surfaces that can shift resistance due to those surfaces;
A) interacting with one another forming higher resistance films;
B) the surfaces corroding independently and increasing resistance;
C) reacting with local water impurities (compounds called "salts of metals" but not sodium all based compounds) that change resistance of the surfaces acting to reduce the conductivity of the stray currents, or galvanic potentials in the build.

I don't have knowledge of the original images' causes. I do have a few decades experience trying to obtain low resistance connections of anodes to welded aluminum hulls so my remarks are generic as opposed to specifically in response to the images shown.

Cheers,
Kevin Morin
Kenai, AK

[OceanTrvlr]

Now THAT's interesting. I had thought some about how clean to make the interface from the anode to the tab on the transom. But now that you illustrate the issue better, I feel that I may need to put some extra effort into making sure that interface is as low-resistance (electrically) as possible.