Over the side extra anode?

[Tranona]

I have seen people hanging anodes over the side and clamping them to the guard rails. It was regularly done on a big 80 foot sailing yacht moored near me. So I guess that boats rails were bonded or he was wasting his time.

I think this is what reinforced my belief that all boat rails were bonded to the anode and/or the keel. I used to have an old Princess 37 that had steel radar arch and steel rails and I think they were bonded. Having read the ABYC recommendations on boat wiring I then assumed all boats were the same. Every days a school day.
On a similar vein, why do we bond fuel fillers and fuel tanks? I always assumed to it was to ground any possible sparks, but a spark will only happen if there is a circuit to complete. Not bonding them would surely be safer, as the fuel filler is connected to the tank via a non conducting rubber pipe and the tanks are usually connected via again non conducting rubber pipes either all the way or part way. Or is there another reason?

For the first it may well be that the rail they are using is then connected electrically to the prop shaft either through the gearbox or using the Duff fitting that has brushes running on the propeller shaft. I have seen similar arrangements on boats with saildrives that live part of the time in fresh water and need to use a magnesium anode. I wire goes to the pushpit mounting stud inside and on the outside is a stud to which the hanging anode cable is clipped when needed.

You are right - Princess and Moody (same factory) used to festoon their boats with unnecessary wires and anodes because they did not understand what they were doing. There is no need to bond tanks, fillers, through hulls to anodes in a grp hull. Post#13 covers most of the situations where anodes are needed in a GRP boat.

I can see the point of giving guard rails a path to earth for lightning protection. Equally anodes are often used now to earth the 240v shorepower system as required by the latest standards. Indeed I did this when installing shorepower on my boat because it was easy and also the method used by Bavaria on my previous boat. However, nothing to do with the anodes for the propeller.

 

[jfm]

... they aren’t connected to your boat ....

They are, by the shore power. That's the whole point behind galvanic (edit: or electrolytic) corrosion aggravated by neighbours. If you're not on shore power you don't need to worry about neighbours, but of course all of us are. That's why people use galvanic isolators or isolation transformers to ensure they're always disconnected from neighbours.

 

[jfm]

Princess and Moody (same factory) used to festoon their boats with unnecessary wires and anodes because they did not understand what they were doing. There is no need to bond tanks, fillers, through hulls to anodes in a grp hull.

I definitely don't want to go over old ground, but just to say that isn't undisputed. Many high quality boat builders disagree with you, and seacocks are usually made from 2 or 3 metals that are touching each other on the dry side. BUT, let's just agree to disagree. I just want to record for future readers that this isn't a universally agreed thing.

 

[Tranona]

They are, by the shore power. That's the whole point behind galvanic corrosion aggravated by neighbours. If you're not on shore power you don't need to worry about neighbours, but of course all of us are. That's why people use galvanic isolators or isolation transformers to ensure they're always disconnected from neighbours.

That is electrolysis rather than galvanic action, although the effect is the same. Galvanic action arises just from the 2 metals being in contact in an electrolyte (seawater).

 

[jfm]

That is electrolysis rather than galvanic action, although the effect is the same. Galvanic action arises just from the 2 metals being in contact in an electrolyte (seawater).

Yup, agreed, and I have edited my post above.
If you don't mind a bit of pedantry, with neighbours it can be galvanic or electrolytic. As you say, the effect and the remedies are the same anyway.

 

[Tranona]

I definitely don't want to go over old ground, but just to say that isn't undisputed. Many high quality boat builders disagree with you, and seacocks are usually made from 2 or 3 metals that are touching each other on the dry side. BUT, let's just agree to disagree. I just want to record for future readers that this isn't a universally agreed thing.

Yes, I am always surprised why the practice continues when there is no theoretical support for it, Beliefs are very difficult to shift once they get embedded. At least in this case it is unlikely to do any harm, but easy to prove they are not needed by removing them and seeing what happens.

As a matter of interest what is happening with your lovely new boat in this respect? I would guess it has rather a lot of through hulls. I assume that the props, rudders, that lifting thing on the stern, the thrusters and stabiliser fins will need some sort of protection if they have mixed metals - stainless and aluminium or bronze. Add it as number 302 on your list of discussion points with them.

 

[mrangry]

Forgive my poor grasp of this subject before I begin. I am currently replacing the 30mm shaft on my Beneteau due to crevice corrosion where the volvo seal seals on the shaft causing the dripless seal to drip. The prop anode had fallen off a few months prior to me lifting her out. Although the anode was missing, the bolts were still there so can only assume that the anode has rotted at the securing bolts and fallen off leaving me with zero protection on the shaft. Maybe duralac next time?

I have considered hanging an anode off the boat when berthed in the marina, but thinking about it will electrons not take the path of least resistance, which is always going to be through the 30mm stainless shaft as opposed to a large anode on a length of say 5mm flex.

 

[kashurst]

Crevice corrosion is usually caused by lack of oxygen in the water surrounding the stainless steel. Tricky to stop but lack of use for long periods can cause this problem. I don't think that problem is related to your anode disappearing.
Your anode dropping of the prop nut is caused by the anode being used up protecting the shaft/propellor combination which is normal, I guess it disolved faster than you expected. I have found prop nut anodes a bit useless as they are not very big and as they disolve come loose and fall off or break. I fitted shaft anodes as well as insurance.
The other thing to consider is a galvanic isolator in your shorepower earth line. I found that and antifouling shafts and props appropriately made anodes last longer so again you are less likely to get caught out.

 

[jfm]

Yes, I am always surprised why the practice continues when there is no theoretical support for it, Beliefs are very difficult to shift once they get embedded. At least in this case it is unlikely to do any harm, but easy to prove they are not needed by removing them and seeing what happens.

As a matter of interest what is happening with your lovely new boat in this respect? I would guess it has rather a lot of through hulls. I assume that the props, rudders, that lifting thing on the stern, the thrusters and stabiliser fins will need some sort of protection if they have mixed metals - stainless and aluminium or bronze. Add it as number 302 on your list of discussion points with them.

Your "no theoretical support" view is your view and that of others, but far from the view of everybody, including me These things are not beliefs; they are science.

I think that Sanlorenzo bond everything, including seacocks as standard spec, but let me check - I'm there the week after next. Unavoidable to have several mixed metals as you say.

By the way, Sanlorenzo fit and isolation transformer on the shore power - a chunky thing because 3 phases.

 

[jfm]

will electrons not take the path of least resistance, which is always going to be through the 30mm stainless shaft as opposed to a large anode on a length of say 5mm flex.

If it was an equal race, electrons would tend to take the path of least resistance, but would not do so exclusively - it's the reciprocal addition thing from gcse physics.

But that's irrelevant because it is not an equal race. The electrons from the anode are falling down a much steeper gradient or have a much stronger tailwind, because of where they are starting from, which is a metal with low nobility - ie the metal is more negative, so it wants to be the anode in the circuit, which means it sheds metal rather than collecting it.

In determining who wins the race, the resistance is much less relevant than the gradient or tailwind caused by the low nobility of the anode metal.

 

[Tranona]

Your "no theoretical support" view is your view and that of others, but far from the view of everybody, including me These are no beliefs; they are science.

I think that Sanlorenzo bond everything, including seacocks as standard spec, but let me check - I'm there the week after next. Unavoidable to have several mixed metals. They fit isolation transformer on the shore power - a chunky thing because 3 phases.

Perhaps I should have explained what I meant by beliefs. Yes, you have mixed metals within ball valves (although not all nowadays) and that if they were in seawater there theoretically may be a galvanic circuit. The "belief" is whether this actually happens in practice and bonding to an anode somewhere on the hull prevents it. The empirical evidence suggests not as there are literally hundreds of thousands of through hulls and valves NOT connected to anodes - far more than are - and yet failure of the valve and its internal components is vanishingly rare. The failure if any is in dezincification of the plain brass fittings (hose tails and skin fittings) still used by many - and no anode will protect from this. Where valve mechanisms have failed, and it mainly affects gate valves, is where components are mild steel and rust, or with ball valves, failure of the plating on the ball, again neither of which will be prevented by an anode on the hull.

For a condition that science predicts to be acted upon, it must first be tested, and I have yet to see any convincing evidence that bonding through hulls and valves connected to them has any impact. Of course the glib answer would be "we always bond through hulls and valves and have never had any failures", Just recently I was looking at the latest HR 69, an enormously complex boat by sailing boat standards. Not a single anode except on the propeller, shaft and bow thruster, despite a large number of through hulls. Their "belief" is that they don't need bonding, and yet I am sure they have access to the same science as everybody else.

 

[jfm]

As said a few posts above, I definitely don't want to have this debate again We have done it to death

BTW, I have met Magnus Rassy at a dinner a few years ago (very nice guy) and I believe he will be on a dinner table that I'm on next week, so I'll ask him about this and report back.

 

[GrahamHR]

No, stainless is OK. That is what MG Duff use for their hanging anode kit.

Stainless Steel is a pretty poor electrical conductor; Cheap compared to inconel alloys and the like I suppose.