Anode/Prop Proximity

[duck21]

Hi all,

How far is too far from the prop for the anode to be mounted on the prop shaft? I have about 28" of exposed prop shaft between the strut and the hull. I'd like to have the flexibility of being able to slide the shaft back from the transmission should anything happen with my flexible coupler.

If I mount the anode right next to the strut I lose that flexibility. If I mount the anode up next to the hull is that going to decrease the effectiveness of the anode in preventing any stray current from eating the prop?

I'll note that this is fresh water and I do see some wear on the anode each season. I do not have room for the anode to be placed between the prop and the strut.

Thanks for the insight!
Doug

 

[dLj]

It's always preferred to keep the anode as close to the prop as possible. Can you calculate where on the shaft you would have to put the anode to allow you to still do what you are thinking while keeping it as close as you can to the prop end? I don't think you'd have a problem, but to really know, you would have to do complicated measurements that would be really hard to do even if you had the equipment.

The anode doesn't prevent stray current corrosion, but rather general corrosion and/or galvanic corrosion - just a FYI.

In the case of an anode on your prop shaft with a bronze propeller - if the anode is too far from the prop, the prop can become the sacrificial anode for your shaft.

dj

 

[jssailem]

In fresh water, you want a magnesium anode.

Here is one way it can be done.

They also make collar anodes to fit in narrow spaces.


One source is Magnesium Anodes | BoatZincs.com

 

[Ralph Johnstone]

Is there any chance your shaft is NOT SS ? If bronze, location is not a problem.
But in the boating world, such coincidences just don't occur.

 

[Dalliance]

My magnesium anodes are located about where jssailem has them. You don’t want the anode right at the strut anyway because it could restrict water flow through the cutlass bearing.

 

[duck21]

No such luck, shaft is definitely SS.

Is there any chance your shaft is NOT SS ? If bronze, location is not a problem.
But in the boating world, such coincidences just don't occur.

 

[duck21]

Thanks for the info, all. I was hoping that this was all within the "acceptable distance" range, but I'd rather not trust the waters (so to speak), so I'll plan on installing in the "normal" place. I appreciate the wealth of knowledge/insights.

Doug