Anodes

[Leni]

When our boat was surveyed when we bought her just over a year ago the surveyor noted in his report that she had two pairs of anodes, one pair fore and one aft, and that they were 30% eroded. He said that this was satisfactory, but recommended that on a boat of the length of ours - 55ft - there should be another pair fitted, and recommended that these should be added at the next haul out.

 

My son thinks we don't really need the extra pair, and that the surveyor may have suggested them because he is a Marine surveyor and is more used to surveying sea-going vessels. Which of them is right? And if we do need them, where exactly should the the extra pair fitted?

 

Thanks.

[Proper Job]

I think that the general consensus is that you should have them.

 

Depending on many conditions (water quality, sheet piling, other boats electrical systems, your boats electrical system, shore-power etc, etc) will depend on how long they last. Bottom line is that when they're 'sacrificing' themselves, other vital parts of your boat aren't.

 

IIRC, they're only good for about 10' - 15' protection in either direction from where they're placed, which means that they should be on the sides of most NB's. In practice, they're on the curved sections of the bow and rear swim to avoid them being knocked off, which means that the centre section of the hull isn't protected.

Edited October 31, 2012 by Proper Job

[bizzard]

I think that the general consensus is that you should have them.

 

Depending on many conditions (water quality, sheet piling, other boats electrical systems, your boats electrical system, shore-power etc, etc) will depend on how long they last. Bottom line is that when they're 'sacrificing' themselves, other vital parts of your boat aren't.

 

IIRC, they're only good for about 10' - 15' protection in either direction from where they're placed, which means that they should be on the sides of most NB's. In practice, they're on the curved sections of the bow and rear swim to avoid them being knocked off, which means that the centre section of the hull isn't protected.

I think powerful onboard mains electricity, big inverters and stuff is the main problem. When i work on docked boats the outbreaks of electrolosis pitting are almost always adjacent to powerful mains appliances inside.

[RobinJ]

When our boat was surveyed when we bought her just over a year ago the surveyor noted in his report that she had two pairs of anodes, one pair fore and one aft, and that they were 30% eroded. He said that this was satisfactory, but recommended that on a boat of the length of ours - 55ft - there should be another pair fitted, and recommended that these should be added at the next haul out.

I think the key here is reccomended!

As has been said, anodes sacrifice themselves to protect the hull, but can only cover maybe 20'?

Provided you have space to fit them (e.g. V hull design).

Provided you haven't got an epoxy anti corrosion paint.

Provided you moor up next to metal piling etc.

Then why not?

[Leni]

Thank you all.

 

So, if it's recommended that we have a third pair of anodes fitted somewhere between the fore and aft pair to ensure protection for the entire length of the boat, where do they go? Given that the fore and aft pairs are under the curve of the hull, where do the middle pair go so that they don't stick out at the sides and get knocked off? Sorry if I'm being stupid and missing something obvious!

[Grace and Favour]

Thank you all.

So, if it's recommended that we have a third pair of anodes fitted somewhere between the fore and aft pair to ensure protection for the entire length of the boat, where do they go? Given that the fore and aft pairs are under the curve of the hull, where do the middle pair go so that they don't stick out at the sides and get knocked off? Sorry if I'm being stupid and missing something obvious!

 

That's exactly the reason why your boat may not have a central pair!

[Machpoint005]

Why put them in pairs? How about one on one side, a third of the way back, and one on the other side, two-thirds of the way back?

 

...they do come in different shapes, IIRC.

[BEngo]

Thank you all.

 

So, if it's recommended that we have a third pair of anodes fitted somewhere between the fore and aft pair to ensure protection for the entire length of the boat, where do they go? Given that the fore and aft pairs are under the curve of the hull, where do the middle pair go so that they don't stick out at the sides and get knocked off? Sorry if I'm being stupid and missing something obvious!

 

 

Stick them on the base plate, but not opposite each other, stagger them so that one is about 10 feet ahead of the other. The front one wants to be about 10 ft back from the one one the bow.

 

Or, stick them on the sides, at the bottom, by the base plate and have some protective angle welded in front of them. Stagger them as above. If you do this use the 'flat' shaped ones not the rounded ones, and check the overall width does not exceed 6ft 10in. Many boat baseplates are 6ft to 6ft6in wide and the boat tapers down from the top rubbing strip to the baseplate, so an anode can be fitted without the boat getting over wide.

 

N

[Timleech]

Stick them on the base plate, but not opposite each other, stagger them so that one is about 10 feet ahead of the other. The front one wants to be about 10 ft back from the one one the bow.

 

Or, stick them on the sides, at the bottom, by the base plate and have some protective angle welded in front of them. Stagger them as above. If you do this use the 'flat' shaped ones not the rounded ones, and check the overall width does not exceed 6ft 10in. Many boat baseplates are 6ft to 6ft6in wide and the boat tapers down from the top rubbing strip to the baseplate, so an anode can be fitted without the boat getting over wide.

 

N

 

M G Duff are now selling a thin flat anode with chamfered edges especially for fitting to the sides of canal boats. They are ridiculously expensive, per kilo of Mg, compared with the ordinary anodes.

 

Tim

Edited October 31, 2012 by Timleech

[Proper Job]

Why put them in pairs? How about one on one side, a third of the way back, and one on the other side, two-thirds of the way back?

 

...they do come in different shapes, IIRC.

Not sure if this is an old wives tale, but I was once told that anodes effectiveness drops considerably once you move out of 'line of sight'.

 

This is why they put them in pairs. One on one side with nothing on the other side will not protect the side that has nothing. It's also why putting them on the curve of the bow/swim has only limited effect for protecting the sides

[Guest]

 

We no longer connect to shore power. Nor does any boat that moors within our vicinity. (our LTM's don't have shore power)

 

Do we still need to have anodes?

 

I realise a surveyor may say we need them when we come to sell (for the benefit of the buyer who may moor with shore power)

 

- but in the meantime? - what use do they serve?

[RLWP]

 

We no longer connect to shore power. Nor does any boat that moors within our vicinity. (our LTM's don't have shore power)

 

Do we still need to have anodes?

 

I realise a surveyor may say we need them when we come to sell (for the benefit of the buyer who may moor with shore power)

 

- but in the meantime? - what use do they serve?

 

In theory - yes. They have nothing to do with shorelines or anything else

 

They work the same way as your Grannie's galvanised council dustbin did - the zinc corrodes before the steel in a little galvanic cycle all it's own

 

In practice? I have well-expressed thoughts on the matter. I would note Grannie's dustbin was entirely covered in zinc and not painted*

 

Richard

 

*except for the house number on the side

[trackman]

Had CN blacked earlier this year. After she was jetwashed it was clear that there were better protected areas around each anode. I reckoned these went to no more than 3m from the anode in each case, leaving a lot of boat without good protection. I have had 2 more anodes fitted, at the yard's suggestion, one at the midpoint of each side. We'll see how that works in a couple of years.

[Guest]

Had CN blacked earlier this year. After she was jetwashed it was clear that there were better protected areas around each anode. I reckoned these went to no more than 3m from the anode in each case, leaving a lot of boat without good protection. I have had 2 more anodes fitted, at the yard's suggestion, one at the midpoint of each side. We'll see how that works in a couple of years.

 

Do you connect to shore power?

[trackman]

No, we've never connected to shore power. The corrosion is not serious I'm pleased to say, but I just felt it worth the fairly small extra cost of the additional anodes for some added peace of mind.

[Guest]

No, we've never connected to shore power. The corrosion is not serious I'm pleased to say, but I just felt it worth the fairly small extra cost of the additional anodes for some added peace of mind.

 

Thanks

[Leni]

Thanks very much everybody for some really useful and thought-provoking responses. I think we'll probably go for the extra anodes, just to be on the safe side, when the boat is next blacked. We don't use shore power (and in all honesty are never likely to) but I think it sounds as if it's 'better to be safe than sorry' anyway.

 

Once again, thanks to all who've contributed their thoughts

[RLWP]

Are you safer though? What if the increase in width of your boat means you hang up in a lock?

 

Richard

[blackrose]

Do you connect to shore power?

 

They have nothing to do with shorelines or anything else

 

Edited November 2, 2012 by blackrose

[blackrose]

M G Duff are now selling a thin flat anode with chamfered edges especially for fitting to the sides of canal boats. They are ridiculously expensive, per kilo of Mg, compared with the ordinary anodes.

 

Tim

 

I bought some large, flat, 1" thick anodes with chamfered front and back edges from Amber Boats of Evesham a few years ago after seeing them on one of their show boats at Crick. They were reasonably priced, but as a boat builder they thought it was an unusual request.

 

I had 2 welded amidships on each side of the hull, resting on the protruding baseplate which protects them from getting knocked off. I'm not sure if Amber are still in business?

 

 

As PJ has already mentioned, anodes aren't supposed to work around corners so welding them to the baseplate might only protect the baseplate.

 

Here are the ones Tim mentioned at the bottom of page 2/3: http://issuu.com/mgduff/docs/new-products-for-2012?mode=window&backgroundColor=%23222222

 

Even if they're expensive I'd still fit one on each side. Over 5 or 10 years the extra cost is negligible and certainly far less than hull repairs.

 

When my boat first came out of the water the steel plate was perfect everywhere except for the middle of the boat on both sides where there were no anodes and the first signs of pitting.

Edited November 2, 2012 by blackrose

[Keeping Up]

Perhaps I'm wrong but I'd have guessed that no more than one narrowboat in a hundred has anodes fitted anywhere other than bow and stern.

[Proper Job]

Perhaps I'm wrong but I'd have guessed that no more than one narrowboat in a hundred has anodes fitted anywhere other than bow and stern.

You're probably right, but had I known about those slim ones I'd have fitted a pair midships when she was out for blacking a few weeks back.

 

Ocelot had negligable pitting on the sides at the bow and stern, but although nothing to worry about, there was pitting midships

 

A couple of hundred extra pounds every couple of years is a lot cheaper than replating in 20 years time

[Bullfrog]

Our little boat balances up your opinion Alan, with 10 in total 8 on the hull and 2 on the rudder.

 

You will remember from previous posts that these have been well used with 3 of them fizzing away within about 18 months. I still think that was because of external conditions at our moorings. BWML are currently replacing the site electrics because of "faults"!

 

David

 

 

 

 

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[ditchcrawler]

I bought some large, flat, 1" thick anodes with chamfered front and back edges from Amber Boats of Evesham a few years ago after seeing them on one of their show boats at Crick. They were reasonably priced, but as a boat builder they thought it was an unusual request.

 

I saw those and made a note. I wish I had bough some now.

[Timleech]

I saw those and made a note. I wish I had bough some now.

 

Here are some at midland chandlers.

At that price they cost £21.60/kg, whereas 3.5 kg ordinary flat anodes from the same source are £13.40/kg.

 

Tim