Anode Location

[JSYmartini]

I have three, 4KG anodes on my transom (twin shaft semi-D) as well as button anodes on my rudders.

The button anodes need replacement every year but the big ones don't seem to be doing much at all.

Some people seem to say that the anodes need to "see" the parts they are trying to protect but others don't think it matters. Looking round the boat yard seems to prove this as well.

Is there a general consensus? A theory behind one or the other?


I'm getting close to drilling some holes in the bottom of the boat, outboard of the prop shafts and moving 2 of the transom anodes there.

Am I wasting my time or not?

Thanks

 

[Tranona]

The anodes on your transom are probably not doing anything. You are correct, they should be in line of sight to what they are protecting, presumably the props. So one either side on the bottom near the props and bonded to their respective shafts.

 

[vyv_cox]

One thing you can be sure of - looking around at other boats will give you as many wrong solutions as right ones. The 'line of sight' instruction is well proven, because electrons travel in straight lines in seawater, with a very few exceptions.

 

[JSYmartini]

Thanks for the replies.

The way I'm looking at it - an anode has a certain "range" of effectiveness, anything within range would be protected. But as you get to the outer limits of this range, the protection would be reduced. If electrons did go round corners for arguments sake, to a lesser or greater degree - having to do so must drastically reduced that range further.

I'm convinced now it's the right thing to do. I'm having to replace all 20 of my P bracket bolts, several came off in my hand when I got access to the inside. Admittedly they are 36 years old, one of my bonding wires came adrift during last season, bound to cause problems.

Also finding a bit of pink on the P brackets, only surface, a going over with my orbital sander got rid of it but shows that the whole underwater protection system needs looking at.

My seacocks are bonded as well but sod it, I'm keeping them that way. I know about the modern school of thought but I'm not 100% convinced enough to move away from standard practice. If done correctly and maintained properly I hope to survive another 36 years.

Definitely going to keep a much sharper eye on my underwater dangly bits from now on!

 

[VicS]

Thanks for the replies.



My seacocks are bonded as well but sod it, I'm keeping them that way. I know about the modern school of thought but I'm not 100% convinced enough to move away from standard practice. If done correctly and maintained properly I hope to survive another 36 years.

Definitely going to keep a much sharper eye on my underwater dangly bits from now on!

Your choice but be aware that bonding of the seacocks was judged to be one of the contributing factors to the near loss of the F.V. Random Harvest off Brighton a few years ago and that one of the recommendations made by the MAIB in their report on that incident was that they should not be bonded.

 

[Keith-i]

Your choice but be aware that bonding of the seacocks was judged to be one of the contributing factors to the near loss of the F.V. Random Harvest off Brighton a few years ago and that one of the recommendations made by the MAIB in their report on that incident was that they should not be bonded.

But was that not more as a safeguard against people incorrectly connecting their bonding wire to a positive power source on board, rather than as a means to safeguard skin fittings against corrosion. IMV, bronze fittings should sit quite happily unbonded if they are not electrically connected to any other less noble metal.

 

[VicS]

But was that not more as a safeguard against people incorrectly connecting their bonding wire to a positive power source on board, rather than as a means to safeguard skin fittings against corrosion.

I dont think you will find anything like that is mentioned in the report.

There were several contributing factors but the fitting which failed was not in fact very old. You would not expect it to have failed due to simple dezincification in the time that it had been in service. The corrosion had therefore probably been accelerated due to electrolysis as a result of the poor standard of wiring on the vessel. If the fitting had not been electrically bonded it is unlikely that it would have suffered from electrolysis.

 

[johnwest]

I have three large anodes, two on transom, one underneath between the shaft brackets. One on each shaft and one on each stainless steel rudder. On my annual lift both shaft anodes are very eroded and both rudder anodes have virtually disapeared. The three hull anodes have little wear so a quick clean with a brass brush, and are replaced after about three years.

j

 

[JSYmartini]

I have three large anodes, two on transom, one underneath between the shaft brackets. One on each shaft and one on each stainless steel rudder. On my annual lift both shaft anodes are very eroded and both rudder anodes have virtually disapeared. The three hull anodes have little wear so a quick clean with a brass brush, and are replaced after about three years.

j

The large anode underneath goes at the same rate as the 2 on the transom?