Fitting a Zinc Anode question

[bony]

A64pilot
"May be that you do not need a longer shaft, just a proper taper?
I would not do anything to cause me to move the rudder, I’d fit a hull zinc before I did that.
You don’t want too much shaft overhang, you will get prop vibration. If you do.
Also you can fit a prop nut zinc if you don’t have room for a collar zinc".

Thanks. I'm not sure if there's enough room between prop and rudder for a nut zinc, but then again I don't really know how much space they need.

GordMay,
Thanks for the diagram, it will come in handy.

foggysail,
"Also recommend that you measure the system's performance with a half bridge to verify your anode is doing its job."

Can you explain what a half bridge is and how you go about measuring with it, I've never heard the term before. Perhaps you can point me to a website on the subject. I don't have much knowledge about anodes a bonding systems and will need to do more reading on the subject.

Cheers.

[foggysail]

A simple explanation ---A half bridge is made when a reference cell is placed in a conductive solution, the same solution as a boat's exposed metals. With the reference cell in the water you will read a voltage between the reference cell and the particular exposed metals being measured. The exposed metals are one part of the bridge and the reference cell is the other.

http://chem320.cs.uwindsor.ca/Notes_files/320_l14.pdf


Safe voltages that prevent galvanic corrosion are published in many books on the subject. Some of reference cells include one called calonel and another is a silver-silver chloride cell. They even have a copper reference cell.

An anode, zinc or aluminum (my preference) will cause a more negative voltage reading between the reference cell and the exposed metal IF the anode is adequate. If not, you invite galvanic corrosion. You need to do some reading on this.

[bony]

Thanks foggysail,

I will need to do quite a bit of reading I think. Thanks for the explanation and advice.

bony

[frant]

Bony, I have recently developed a Saildrive leg Corrosion Protection monitoring kit and anode booster. This same kit could be used to monitor and provide catholic protection for shaft drive prop systems. PM me if interested and I can email details.

[boatpoker]

Originally Posted by frant

Bony, I have recently developed a Saildrive leg Corrosion Protection monitoring kit and anode booster. This same kit could be used to monitor and provide catholic protection for shaft drive prop systems. PM me if interested and I can email details.

You mean an impressed current system ?

[frant]

Originally Posted by boatpoker

You mean an impressed current system ?

No not an impressed current system. Use an aluminium anode suspended over the side. Our aluminium anodes are slightly more electronegative than the aluminium split ring anodes and have a lower internal resistance therefore will tend to protect/extend the life of the splitring anode whilst deployed. When underway the splitring anode only is consumed. The monitoring meter and Ag/AgCl reference electrode enable the potential of the Saildrive leg with and without the booster anode to be monitored and the current from the booster anode to be measured.

[boatpoker]

Originally Posted by frant

No not an impressed current system. Use an aluminium anode suspended over the side. Our aluminium anodes are slightly more electronegative than the aluminium split ring anodes and have a lower internal resistance therefore will tend to protect/extend the life of the splitring anode whilst deployed. When underway the splitring anode only is consumed. The monitoring meter and Ag/AgCl reference electrode enable the potential of the Saildrive leg with and without the booster anode to be monitored and the current from the booster anode to be measured.

So the reference cell is permanently affixed ? how ? where ?

[bony]

Originally Posted by frant

Bony, I have recently developed a Saildrive leg Corrosion Protection monitoring kit and anode booster. This same kit could be used to monitor and provide catholic protection for shaft drive prop systems. PM me if interested and I can email details.

Thanks frant, I'll keep it in mind. I need to do a lot of reading on this subject to get my head around it. It's all a learning process for me at the moment.

I took the prop off and cleaned it up and tapped it (gently) with a hammer. It rang like the bells of St Clement's so, according to dsharp's advice, it might still be ok.

The prop shaft though is kaput. I cut the corroded end off it and, you fellas were right, the corrosion has chewed right into down the centre. The outside of the shaft and taper still look serviceable but the guts of it is no good. Dimensions are 45"x1" and I think I can get a new one here in Ozzie land for around AU$250. A rather expensive way to learn the importance of anodes it seems.

[newhaul]

Originally Posted by bony

Thanks frant, I'll keep it in mind. I need to do a lot of reading on this subject to get my head around it. It's all a learning process for me at the moment.

I took the prop off and cleaned it up and tapped it (gently) with a hammer. It rang like the bells of St Clement's so, according to dsharp's advice, it might still be ok.

The prop shaft though is kaput. I cut the corroded end off it and, you fellas were right, the corrosion has chewed right into down the centre. The outside of the shaft and taper still look serviceable but the guts of it is no good. Dimensions are 45"x1" and I think I can get a new one here in Ozzie land for around AU$250. A rather expensive way to learn the importance of anodes it seems.

better than loosing the screw in heavy weather on a windward shore