Hanging zinc what am I missing

[arch007]

I am wondering why I need zinc on the propellar if I use a
Hanging zinc attached to the prop shaft.

What am I missing ?

Why do I need a prop zinc. I spend 95 per of the time in a marina.

[a64pilot]

You shouldn’t, but if it’s wasting away, that’s telling me you do. My guess would be that your hanging zinc isn’t connected well to the shaft.
However stainless steel is a poor conductor, but it seems all hanging zincs cables are made from SS?
It would seem that a hanging zinc is at a disadvantage right from the beginning.

[tkeithlu]

Can you borrow a silver test anode? They cost about $125 fro firms that make zincs, but for my steel boat that's a necessary expense. If you or a yard has one, you can check the effectiveness of your anode array.

In the general case, why not? a zinc collar on your shaft will cost a few dollars, give you that priceless peace of mind, and still be there next year if you didn't need it.

[GordMay]

Silver/Silver-Chloride Reference Electrode
➥ https://www.boatzincs.com/corrosion-...ode-specs.html

➥ https://www.corrosion-doctors.org/Co...lls-Silver.htm

[fstbttms]

The further from the part being protected and the longer the electrical path between part and anode, the less protection is provided.

[S/V Illusion]

Originally Posted by arch007

I am wondering why I need zinc on the propellar if I use a
Hanging zinc attached to the prop shaft.

What am I missing ?

Why do I need a prop zinc. I spend 95 per of the time in a marina.

Unless you know the resistance between the prop and anode, no one can answer the question intelligently.

[bobgarrett]

Some props are electrically isolated from the shaft and boat.

[fstbttms]

Originally Posted by bobgarrett

Some props are electrically isolated from the shaft and boat.

That seems unlikely. Examples?

[a64pilot]

Originally Posted by fstbttms

That seems unlikely. Examples?

Not the shaft, but many boats have a plastic flex coupling between the transmission and the shaft coupling, it’s there to absorb vibrations and to fracture hopefully before any major damage is done if you pick up a line etc, if a jumper wire isn’t installed to bridge the coupling then the shaft and prop is isolated.

I assume many may not know to install the jumper wire?

[Mr O]

After installing a flexible shaft coupling, I thought there was no need for a zinc over the side wired to the shaft. I left it isolated from the transmission as my boat is not a bonded system. What is the point in having zincs on prop and inner end of the shaft? Maybe if your prop zinc is gone?

[fstbttms]

Originally Posted by Mr O

After installing a flexible shaft coupling, I thought there was no need for a zinc over the side wired to the shaft. I left it isolated from the transmission as my boat is not a bonded system. What is the point in having zincs on prop and inner end of the shaft? Maybe if your prop zinc is gone?

Hanging a "fish" anode from the shaft is never the preferable way to protect your prop and shaft. Underwater metals should be protected by an anode attached directly to the part in question.

[a64pilot]

A prop zinc is just too easy, and not expensive.
Crazy not to have one, running gear is just too expensive to not protect.

[singlespeed]

We were docked for almost three months refinishing the interior woodwork on our boat. I dove on the boat monthly to keep growth on the running gear and inlets. Near the end of our stay, a transient boat was moved one slip over from us. Getting ready to leave the marina, I dove for a final inspection. Imagine my surprise when I found all my anodes heavily pitted. Since the only change near our boat was the new transient boat, a quick check with a volt meter found stray current on both sides of the transient boat. Moral, don't skimp on anodes. Cheaper than replacing running gear.

[fstbttms]

Originally Posted by singlespeed

Moral, don't skimp on anodes. Cheaper than replacing running gear.

Good advice but in the presence of stray current, even a proper compliment of anodes may not be enough.

[bobgarrett]

Originally Posted by fstbttms

That seems unlikely. Examples?

Volvo saildrives are insulated from the engine to reduce electrolysis.

And their propellors similar -to quote Volvo...
"Hubs for saildrive propellers include a shock-absorbing rubber bushing to minimize stress on the drivetrain caused by gear changes. In addition, the bushing is designed to galvanically isolate the propeller from the saildrive - preventing galvanic corrosion caused by the propeller."