Beta 14 eating anodes at a blistering rate

[Wotname]

Originally Posted by scuttlebooty

....

Yes that is correct.

OK so as the anode is in the raw water side and if you have a breach between this and the coolant side, you are in effect exposing the anode to all the dissimilar metals that might be present in the coolant side.

I'm not saying this your problem but it is something to be aware of and perhaps check.

[scuttlebooty]

As mentioned before none of the thru hulls are bonded, and the proper shaft is electrically insolated from the engine block. I added a hanging zinc to try and save the engine zinc.

However, my knot-indicator (whatever it's called) has never worked (mechanically jammed), but perhaps that could provide a path if it was somehow electrically compromised.

The pencil zinc is located just up stream of the HX stack, in the raw water side of course.

[boatpoker]

Originally Posted by scuttlebooty

Back on topic:

I'm actually not sure how stray current from within the boat could be causing the problem. If I understand correctly, the zinc will corrode in a stray current condition only if the current is flowing from it, and to the electrolyte. In other words, if a piece of stainless steel and zinc are placed in salt water, with the positive end of a battery connected to stainless and the negative to the zinc, it will be the stainless that corrodes.

Absolutely not. The stainless is the cathode and the zincs, aluminum or magnesium are the anodes. Take a look at the Noble Scale (Galvanic Scale).

https://en.wikipedia.org/wiki/Galvanic_series

[Wotname]

Originally Posted by scuttlebooty

..... If I understand correctly, the zinc will corrode in a stray current condition only if the current is flowing from it, and to the electrolyte. In other words, if a piece of stainless steel and zinc are placed in salt water, with the positive end of a battery connected to stainless and the negative to the zinc, it will be the stainless that corrodes.
.........

Originally Posted by boatpoker

Absolutely not. The stainless is the cathode and the zinc is the anode. Take a look at the Noble Scale (Galvanic Scale).

https://en.wikipedia.org/wiki/Galvanic_series

I think you misunderstood Scuttle's example. In this case, the Noble scale is not the issue, it is a simple potential difference provided by the battery and the electron flow will be from the zinc (-ve pole) to the stainless (+ve pole). Or more correctly, the ions will the carrier in seawater.

[boatpoker]

Originally Posted by Wotname

I think you misunderstood Scuttle's example. In this case, the Noble scale is not the issue, it is a simple potential difference provided by the battery and the electron flow will be from the zinc (-ve pole) to the stainless (+ve pole). Or more correctly, the ions will the carrier in seawater.

I don't think I misunderstand. The zinc simply cannot cause corrosion of the stainless. The Galvanic scale is indisputable inescapable fact.

[Wotname]

Originally Posted by boatpoker

I don't think I misunderstand. The zinc simply cannot cause corrosion of the stainless. The Galvanic scale is indisputable inescapable fact.

Well then it must be me who doesn't understand!

[Wotname]

Originally Posted by scuttlebooty

..... If I understand correctly, the zinc will corrode in a stray current condition only if the current is flowing from it, and to the electrolyte. In other words, if a piece of stainless steel and zinc are placed in salt water, with the positive end of a battery connected to stainless and the negative to the zinc, it will be the stainless that corrodes.

..........

Ahh... I see where I went wrong earlier, I misunderstood the above post - I got poles back to front

Yes the zinc will corrode away when the current (electron flow) is flowing from it. In scuttle's example above, it states the negative pole is connected to the zinc and the positive to the stainless steel. Remembering electrons flow from the negative pole to the positive pole (in the external circuit), the zinc will have the current flowing from it and the stainless will have the current flowing into it.

[scuttlebooty]

Yes sorry for the confusion. It's the electron flow that matters, and if the electrons are flowing from the zinc, then it would be the zinc that corrodes, and vice versa if it were the stainless steel.

So to correct my statement, stainless steel connected to the negative terminal and zinc to the positive will result in the stainless cording, not the zinc.

[scuttlebooty]

For reference, here a few photos of the cooling system and the zinc placement in the engine. The 3D rendering is for a newer version of the engine, where the HX was redesigned and the zinc placed down stream of the HX stack.

The other image shows my heat exchanger design from the spares manual, and here the zinc placement is upstream of the stack as it is in my engine as well.

[guyrj33]

the zinc on my heat exchanger also wastes away faster than others. My heat exchanger is made from a combination of metals and it's only connection to the engine and the rest of the boat is thru seawater, coolant and rubber hose. I assume the zinc is consumed by the use of multiple metals in the heat exchanger it'self.

[a64pilot]

Temp could also have an effect, I’m not sure how much though.

[sy_gilana]

Last time I found the culprit to be a faulty tempreature sender unit.

Check that and the oil pressure sender. They should be the 2 wire type, not using the block to return.

[richardhc]

I had a similar problem; also never in a marina. Turned out the solar panel frame was grounded to the negative through the stainless mount. Disconnected the stainless mount. Problem over.

[Corrosion-Eng]

The CAUSE is stray current via the water generated by your vessel. It can be eliminated, permanently. The corrosion is marine electrolysis created by the stray current. Use Google to search for marine electrolysis and click on Conquer marine corrosion CAUSE.

[sailorchic34]

Originally Posted by a64pilot

I thought electrical connection was what was relevant, not physical proximity?

Physical proximity is important. I suspect on the typical boat, having the zinc fish, within 10 ft of the prop shaft would be good enough in saltwater. I base this upon my experience with buried Pipelines that have the zinc anodes 25 feet away from the pipeline, connected by wire to the pipeline and it protects about 150-200 feet of pipeline. Saltwater being more conductive should make that work a bit better.

One other possibility to the o p if he has solar is to check the charge controller. He might have a bad capacitor or a bit of corrosion causing a leak to ground. Possibly by using a cheap charge controller temporarily and seeing if the engines zinc lasts longer. I agree the alternator and inverter would be the other primary suspects.

Is the boat bonded. That is are all the through holes,etc. Bonded to ground. it could also be that the engine zinc, is slightly more negative on the galvanic scale so it goes first. Especially if you're using a aluminum fish zinc. As the zinc in the engine will go away first. So you really want a zinc fish hanging over the side and not aluminum.

Edit: just caught up with some of the other postings. with a prop shaft isolated from the engine a fish zinc hanging over the side won't do much. you might try adding a bonding wire across the flanges, to bypass the isolator on the prop shaft