Another Anode Question

[makingplansfor]

My shaft and therefore prop is electrically isolated from the engine presumably because of the coupler. The shaft anode is usually well eroded whilst the big pear anode has little wear. This year I thought I would share the load between the anodes whilst alongside by a jumper between the prop side of the shaft and the inboard stud of the pear anode. On lift out, there was more than usual erosion of the pear anode, but the shaft anode was completely gone! Of course it could have fallen off but I am assuming that something has made the situation worse than previous years? Have I done something silly in connecting the second anode?

 

[VicS]

My shaft and therefore prop is electrically isolated from the engine presumably because of the coupler. The shaft anode is usually well eroded whilst the big pear anode has little wear. This year I thought I would share the load between the anodes whilst alongside by a jumper between the prop side of the shaft and the inboard stud of the pear anode. On lift out, there was more than usual erosion of the pear anode, but the shaft anode was completely gone! Of course it could have fallen off but I am assuming that something has made the situation worse than previous years? Have I done something silly in connecting the second anode?

the hull anode is presumably bonded directly to the engine or gearbox and does not share its wiring with any current carrying part of the DC system.?

shorepower?

youve done what I am sure everyone would suggest.

maybe fallen off maybe an obscure fault or something not anticipated.

 

[vyv_cox]

Most decent shaft anodes have a steel strap cast into the zinc to provide mechanical strength. Even if all of the zinc has corroded away the strap should remain. It sounds possible that your anode has fallen off. When fitting a shaft anode use a hammer in each hand. Bang the two halves together, tighten the bolts. Repeat until no more tightening is possible. An anode fitted like this will never fall off.

 

[makingplansfor]

Thanks - it was an MG Duff anode so I guess it must have dropped off. I count myself lucky then that there wasn't any damage!!

 

[Sinbad1951]

How have you attached the 'bridge' wire from the internal pear anode stud to the shaft? I assume that you are using some form of electrical 'brush'. If this is the case and you should have a good connection between the pear anode and the shaft/prop. However this is easily checked using a multimeter set to ohms. (pm if you would like details on how to do this)
If a good electrical connection then the anode is doing its correct job. However if the connection is not good there may be external factors such as stray current corrosion at work. First check the efficacy of the anode to the shaft and be aware that sometimes altho the stud will be giving an excellent bonding result, the anode may be fouled at the stud by calcium deposits. This requires annual removal of anode and cleaning of stud, washers and nuts.