Can you have too much of a good thing?

[Wobbly Dick]

Hi,

 

I have looked at a boat and the hull was in a bad way. I was told that the Anodes should have been replaced.

 

After it was explained to me what the Anodes do and that they are sacrificed for the sake of the hull, I started thinking if you had more, would it be better? Comments please?

[Breals]

Did you get a survey done, or did the hull just look very rusty (might look a lot worse than it is).

 

I suppose more anodes would in principle provide more protection but regular blacking is probably even more important. Over to the experts -

[John Orentas]

I'm certainly not an expert on this but if we are to assume people who build oil rigs and the like are then the principle must be 'the more the better' such structures are oten totally covered with anodes.

 

The econonomics are of course totally different, as Breals suggests in the case of narrowboats your money may be better spent on more frequent painting.

 

Wobbly, a hull that is covered in rust does not neccesarrily mean the hull is in a bad way, the steel when the surface rust is blasted away by some means can give a very good key for a paint finish.

Edited April 29, 2006 by John Orentas

[Guest]

I have only used small amounts on cars, but am informed that converters such as Fertan (spelling) do a good job on surface rust. I will try it when the day arrives.

[Amicus]

The problem with anodes on a narrow boat is you can attach them only on the ends of a boat, on the swims. If they where on the middle section they would jamb in locks and soon be knocked off. An anode only protects up to a metre or two radius. Definitely have them fitted close to the prop and shaft, after that I dunno.

[John Orentas]

Bit of a new idea this about protecting the propeller and shaft. I have yet to see an example of either of propeller or stainless steel shaft suffering any kind of corrosion even after a couple of decades of being immersed.

 

At one time some builders would fabricate a few recesses into the hull along the length of the boat to take extra anodes, personally I think their effectiveness is marginal at best.

 

I know I have said this before but the ex-owner of my local dry dock, (and he has seen thousands of boats out of the water) believed that anodes contributed to the pitting phenomenon.

[Wobbly Dick]

Hi and many thanks, that's go my brain ticking over

 

The boat I saw was, to my very inexperienced eyes, very rusty, but maybe this could have been mainly surface rust.

The fella, the owner I think, said when it was last blacked, he was told that it didn't need the Anodes replacing, but he said he wished he had.

 

Have Anodes always been used?

 

Is there any difference, and/or benefits, from the bolt on Anodes to the welded on type?

Edited April 29, 2006 by Wobbly Dick

[Bernie]

I do know of some old boaters who have never used anodes and don't believe they do any good, rather they prefer to bottom black every eighteen months to two years and swear by this. The bolt on anodes are much easier to replace.

[Amicus]

Quote from Cornell University publication.

 

 

 

“Generally the worst case for corrosion is when two metals with different stabilities are in close contact. Examples abound from history, including the corrosion of the iron bolts that held wooden ships together when they were in close contact with copper sheathing, put on to protect against barnacles etc. Nowadays, hulls are made of steel and propellors of bronze, so there is a cell at the stern of the ship, and the hull will be attacked and corroded. The answer is to place ``sacrificial anodes" of magnisium or zinc alloys on the hull nearby. Now they are the most anodic metal in the vicinity and will dissolve away, protecting the hull.”

 

http://www.mse.cornell.edu/courses/engri11.../corrosion.html

[alan_fincher]

I have looked at a boat and the hull was in a bad way. I was told that the Anodes should have been replaced.

 

After it was explained to me what the Anodes do and that they are sacrificed for the sake of the hull, I started thinking if you had more, would it be better? Comments please?

 

I'm certainly not an expert on this but if we are to assume people who build oil rigs and the like are then the principle must be 'the more the better' such structures are oten totally covered with anodes.

 

When our boat was surveyed it was found to have 5 anodes altogether, I think, so if you consider the normal places you'd find them, (one each side at front and back), in one case they were doubled up. Our surveyor said they were fine, but that no more should be added, as a boat can be "over-anoded". I wish now I'd pushed him on this point, as considering the chemistry involved, it's rather hard to see how….

 

Bit of a new idea this about protecting the propeller and shaft. I have yet to see an example of either of propeller or stainless steel shaft suffering any kind of corrosion even after a couple of decades of being immersed.

 

I think the point is John that the reaction is the other way. Brass or stainless steel components in the prop and shaft will be fine, I'd have thought, but it's the mild steel hull near to them that will be the one that’s at risk of giving up it's metal. By placing anodes there which are more sacrificial than the steel of the shell, this should help avoid this.

 

I do know of some old boaters who have never used anodes and don't believe they do any good, rather they prefer to bottom black every eighteen months to two years and swear by this

 

I don't know how true it is, but I've heard regularly that boats that are constantly on the move suffer far less bimetallic corrosion than those that spend most of there time tied up. ("The old working boats never had anodes"….. etc, etc). Also that for this reason many hire boat companies don't bother with them, (but boats I've hired clearly have them).

 

But for most privately owned boats, doing "normal" mileages, the strong consensus seems to be that you should have them, and that inspection, and replacement as found necessary at each blacking, should be an essential part of keeping your hull in the best possible order.

[John Orentas]

Hi Alan.

 

Old working boat with few exceptions were not built of mild steel but wrought iron which rusts very little in comparison and as I have said on here a few times consensus engineering is rarely up to much.

 

I take the point about the corrosion of the hull where it is in proximity to the propeller but I must say I have never seen any difference. I don't know if it is just chance but on my boat there is a barely perceptible 'less rust area' approx 500mm radius around my front anodes but that's it.

[DHutch]

Im not sure how true it is a boat can "over annoded"

- If you where to take it to extreames, and cover/coat the whole surface of the boat in anodes, wouldnt that called galavanised!!!

 

Nominally, we have four, in the usuall places.

- Lord knows how affective they are, but there relatively inexpensice, when compair to a new hull, and the surveyer liked them.

 

We black roughtly every 3 years, with twopart pitchfree vinal.

- Every time it comes out (after 3yrs) people are suppresed we're even bothering, and often possativly shocked when we tell them its three years old.

- We planning to be out at worsley again next season, and ill have to take some photos before its done. Its great, even the bottom has almost full coverage still.

 

 

Daniel

Edited April 29, 2006 by dhutch

[DHutch]

Also, the reason for the apprennt "doubleing up" of anodes is that often when they come up for replacment the new anodes are mearly welded next to the old ones, on the assumtion that 'more is better' and there still a fair bit left, so why take them off.

- Then next time you usally remove the times before ones off, and add the new ones there.

 

 

Daniel

[alan_fincher]

Hi Alan.

 

Old working boat with few exceptions were not built of mild steel but wrought iron which rusts very little in comparison.

Hi John,

 

I agree that a great many of the boats were iron, and that it probably lasted a lot better than steel. The sides of my 1898 [approx] ex BCN boat were probably in better shape after 70 years than the steel bottom that had replaced an elm one, and was probably no more than 10 to 15 years old.

 

But, being pedantic, (I'm prone to it, I'm afraid ), I think if you look at something like the ex-GUCC Co carrying fleet built in the 1930s you'll actually find that steel was used more predominantly than iron. My belief is that all the "all-metal" ones, ('Royalty', 'Middle Northwich' & 'Town' classes), were steel, whereas some of the composite boats, ('Star') were built with irron sides, and some with steel.

 

I think 'metal' working boats built after nationalisation, ('River' and 'Admiral' classes), were all also steel, were they not ?

 

But I'm no expert on this, so am more than prepared for someone to jump in and correct me!......

 

Alan

[timboharticus]

I have done some work on pipelines tanks etc.

 

Cathodic protection is recognised as useful. On pipelines it is usually "impressed Current" meaning that a charge controller control voltage between pipe and sacrificial metal (usually a lump of iron or steel).

 

On narrowboat we use magnesium which has more voltage than zinc used on sea going vessels because sea water is more conductive.

 

I don't think that having more anodes would do any harm at all, in fact the more the merrier, and would advise fitting some small ones amidships.

 

On pipelines, tanks it is recognised that a high impressed voltage can damage protective coatings, but having more anodes does not increase the voltage.

 

So, fit lots of anodes and black regularly.

[DHutch]

Anyone tryed geting a NB hotdipped?

[Amicus]

On the question of whether anodes are in fact needed, I'd have thought a long term owner could answer that for his/her boat. On hauling out if the anodes are consumed then they must be doing some good? If on the other hand, after a couple of years in the water they appear "as new" then perhaps they are not needed.

I suspect, also, that the water at the mooring may well have greater effect on corrosion on a particular boat.

[John Orentas]

On the question of whether anodes are in fact needed, I'd have thought a long term owner could answer that for his/her boat. On hauling out if the anodes are consumed then they must be doing some good? If on the other hand, after a couple of years in the water they appear "as new" then perhaps they are not needed.

I suspect, also, that the water at the mooring may well have greater effect on corrosion on a particular boat.

 

 

You could certainly extrapolate that if the anodes are not being consumed they are inactive and therefore not having any effect on anything around them, but can you therefore assume that if your anodes are disappearing the steel from your hull isn't. I am not sure.

 

As for water quality I was moored for a few years close to the dry-dock at Worsley, it was common knowledge there that the boats that regularly moored further up the canal in the crystal clear water in the Patricroft area corroded very badly, in contrast the very local boats in the yellow water at Worsley rusted very little in comparison.

[DHutch]

As for water quality I was moored for a few years close to the dry-dock at Worsley, it was common knowledge there that the boats that regularly moored further up the canal in the crystal clear water in the Patricroft area corroded very badly, in contrast the very local boats in the yellow water at Worsley rusted very little in comparison.

Thats interesting.

- The worsley water is very orange (full of iron oxideness) so i guess it might work like that...?

 

 

Daniel

[Amicus]

You could certainly extrapolate that if the anodes are not being consumed they are inactive and therefore not having any effect on anything around them, but can you therefore assume that if your anodes are disappearing the steel from your hull isn't. I am not sure.

Fair comment

 

As for water quality I was moored for a few years close to the dry-dock at Worsley, it was common knowledge there that the boats that regularly moored further up the canal in the crystal clear water in the Patricroft area corroded very badly, in contrast the very local boats in the yellow water at Worsley rusted very little in comparison.

Tad scary that!