cathodic protection again.

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Pagetslady

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Hi last week while in the IOM i swam under my boat and noticed the Bruntons autoprop anode haad dropped off, it has only been in the water since April and most of that has been in fresh water, I intended to lift out today and put a new one on, but that was not possible, so hope to do it tomorrow, I put my meter from the shaft to the engine earth and was surprised to get a reading of .7 V is this usual or very high. I earthed the shaft to the gearbox and the reading was 0 v I have not had a flexible coupling before so have not had any problem with my fixed prop as it was connected to my pear shaped anode, can I expect to see any damage to my brand new autoprop tomorrow.
Regards Mike.
 
Pagetslady said:
Hi last week while in the IOM i swam under my boat and noticed the Bruntons autoprop anode haad dropped off, it has only been in the water since April and most of that has been in fresh water, I intended to lift out today and put a new one on, but that was not possible, so hope to do it tomorrow, I put my meter from the shaft to the engine earth and was surprised to get a reading of .7 V is this usual or very high. I earthed the shaft to the gearbox and the reading was 0 v I have not had a flexible coupling before so have not had any problem with my fixed prop as it was connected to my pear shaped anode, can I expect to see any damage to my brand new autoprop tomorrow.
Regards Mike.
Click to expand...

Autoprop nickel aluminium bronze ???
I'd expect 0.7 to 0.8 volts if there is still a hull anode connected to the engine earth.

Might be worth bridging the flexible coupling so that the hull anode will act as back up to the prop anode or is there some reason why it should not be bridged?
 
I don't think my Autoprop is nickel aluminium bronze, they only claim 'bronze' so I'm not too sure.

Were the bolts holding the anode on the metal ones or the plastic? Mine were originally stainless steel, which led to rapid corrosion of the anode surrounding them, upon which it fell off early in its first season. If the bolts are still in place then the anode has probably corroded away but if not it has almost certainly fallen off due to undertightening. Nylon bolts were included when I bought replacement anodes, which at least allowed the anode to remain in situ for longer, although they still wasted in a season. I now use a shaft anode as well, which gives me two or possibly three seasons on it and the Bruntons anode.
 
Hi Well I lifted out this morning the Nylon bolts had gone completely so i assume they came undone and the anode fell off, I have now a new one in place and have also fitted a shaft anode, I have also made a small stainless spring that goes under one of the bolt heads that is in contact with the shaft coupling and when tightened is held in contact with the gearbox flange put two on opposite bolts but they only weigh a few grams. I have checked for voltage across the shaft to the engine earth and the reading is 00 so am happy with it I just hope the anode stays on now.
Regards Mike.
vyv_cox said:
I don't think my Autoprop is nickel aluminium bronze, they only claim 'bronze' so I'm not too sure.

Were the bolts holding the anode on the metal ones or the plastic? Mine were originally stainless steel, which led to rapid corrosion of the anode surrounding them, upon which it fell off early in its first season. If the bolts are still in place then the anode has probably corroded away but if not it has almost certainly fallen off due to undertightening. Nylon bolts were included when I bought replacement anodes, which at least allowed the anode to remain in situ for longer, although they still wasted in a season. I now use a shaft anode as well, which gives me two or possibly three seasons on it and the Bruntons anode.
Click to expand...
 
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