Engine anodes - DIY?

[sgr143]

Last season (my first) I found that the pencil anode in my Bukh 20 lasted less than 6 months. I don't know how much less, as there was nothing left when I winterised the engine!

Cheapest ready-mades seem to be £5.24 from ASPA, plus not-entirely trivial postage. Ok, so this is very small beer compared to what I've spent already on fettling this boat - but seeing that a 500mm length of 12mm diameter zince rod can be bought for about a tenner, I wonder whether it's worth cutting such a rod into anode lengths, and drilling, tapping and fitting my own 5mm threads?

Hmmm.. maybe not worth the effort. Thoughts?

Steve

 

[sailorman]

I make my Nanni anode ( exhaust elbow mixer ) from zinc rod from Solent Anodes on ebay, 2 x 250mm rods a tenner & reuse the brass anode housing

 

[PowerSlapper]

SHMO went a stage further. He cast anodes for the DV24 using cast off hull and shaft anodes, faced, drilled and tapped them on a lathe and now has a box of 100+ "Bukh" anodes for the cost of some gas and some plaster (to make the moulds. If you have access to a lathe or drill press and taps and tapping fluid then by all means make some out of rod and save £11.00 per annum. SHMO changes the anodes in his Bukh about 4 times per year though could get away with 2 times. Do not make them too long as there is a cast rib inside the block in line with the anode mounting hole. Also make sure to clean out the debris inside the block where the anode goes. Another point to consider is to fit an external lead from the anode carrier to an earth point on the block. a good electrical connection between the anode and the block is essential for max efficiency.

 

[sgr143]

Many thanks, Jules and SM. Very encouraging. I've bought two readymades, but will go the DIY route the next time around. Though from boughten rod, I think, rather than casting my own! The money saved isn't much but the self-satisfaction will be worth it.

Also very helpful to know how long they last. I guess I should check every couple of months, to be on the safe side.

Steve

 

[vyv_cox]

If casting your own it is advisable not to melt in a steel container. Very small amounts of iron in anodes inhibit their protection. Rod intended for anode use should be to the relevant Mil specification, with very low iron levels.

 

[NormanS]

If casting your own it is advisable not to melt in a steel container. Very small amounts of iron in anodes inhibit their protection. Rod intended for anode use should be to the relevant Mil specification, with very low iron levels.

The anode that I make every year for my propeller, is made from discarded anodes and melted in an old iron ladle, then cast in a treacle tin. None of the above seems to have any detrimental effect on the efficiency of the finished product.

 

[VicS]

The anode that I make every year for my propeller, is made from discarded anodes and melted in an old iron ladle, then cast in a treacle tin. None of the above seems to have any detrimental effect on the efficiency of the finished product.

Vyv is not making this up . The MIL spec calls for an iron content below 0.005%. Even this percentage is only tolerated by having a small cadmium content in the otherwise high purity zinc used .

How are you determining the "efficiency" of your home made anodes?

 

[Mataji]

I recently bought an engine anode from Bukh at Hamble Point together with a few other "genuine Bukh" spare parts. They charged £17.95 for the anode (I omitted to ask the price when ordering). Will this be a better quality anode than the cheaper ones available or have I been stupid? (I actually bought 2, got quite a shock when the package and invoice arrived).

 

[VicS]

I recently bought an engine anode from Bukh at Hamble Point together with a few other "genuine Bukh" spare parts. They charged £17.95 for the anode (I omitted to ask the price when ordering). Will this be a better quality anode than the cheaper ones available or have I been stupid? (I actually bought 2, got quite a shock when the package and invoice arrived).

I don't suppose Bukh make them so no reason to suppose they're any better than anodes made to the relevant spec from other reputable suppliers

http://www.solentanodes.co.uk/products/zinc-pencil-anode-bukh

http://www.solentanodes.co.uk/pages/us-military-specification

 

[NormanS]

Vyv is not making this up . The MIL spec calls for an iron content below 0.005%. Even this percentage is only tolerated by having a small cadmium content in the otherwise high purity zinc used .

How are you determining the "efficiency" of your home made anodes?

I'm not suggesting for one minute that Vyv is "making this up". All I am saying is, that what I do works for me.

I am perfectly capable of determining the efficiency of my anodes, by observing that they get eaten away, and the propeller doesn't. Is there any other way?

 

[Rafiki]

If anyone based in Ipswich wants to cast their own Anodes I have saved most of the ones taken off my boat over the years and you are welcome to them !

Let me know by PM and I will leave them out for you at an agreed time and place - based Fox's.

Regards

 

[sgr143]

Vyv is not making this up . The MIL spec calls for an iron content below 0.005%. Even this percentage is only tolerated by having a small cadmium content in the otherwise high purity zinc used .

I wonder why? I wouldn't have thought that a small amount of iron (50ppm) in solution or even as precipitates in the zinc would make much difference to its electrochemical behaviour... or does it end up on grain boundaries leading to intergranular corrosion? And what does the Cd do?
(I'm not trying to be clever or snarky here, I'm genuinely interested in what might be going on. I'm an academic metallurgist, but from a physics rather than a chemistry background, so corrosion behaviour is a bit outside my home territory.)
Steve

 

[vyv_cox]

I wonder why? I wouldn't have thought that a small amount of iron (50ppm) in solution or even as precipitates in the zinc would make much difference to its electrochemical behaviour... or does it end up on grain boundaries leading to intergranular corrosion? And what does the Cd do?
(I'm not trying to be clever or snarky here, I'm genuinely interested in what might be going on. I'm an academic metallurgist, but from a physics rather than a chemistry background, so corrosion behaviour is a bit outside my home territory.)
Steve

This is all I know. Searches on the specification only seem to find people selling them with no technical info. This one is a bit commercial but there seems to be some fact in there. http://www.boatzincs.com/use_milspec_a18001k.html

 

[NormanS]

This is all I know. Searches on the specification only seem to find people selling them with no technical info. This one is a bit commercial but there seems to be some fact in there. http://www.boatzincs.com/use_milspec_a18001k.html

That's interesting. I have a (bought) pear anode on the hull, which is wired to the engine, and it gets the white coating referred to in your link. The white coating causes very unequal erosion of the zinc. I'm sure we've all seen this on anodes, and are regularly warned not to take it off with a steel wire brush, for fear of contamination.

Conversely, my (home made) conical anode on the propeller, gets almost none of the white coating, and consequently wears away much more evenly. What am I doing right?

 

[VicS]

That's interesting. I have a (bought) pear anode on the hull, which is wired to the engine, and it gets the white coating referred to in your link. The white coating causes very unequal erosion of the zinc. I'm sure we've all seen this on anodes, and are regularly warned not to take it off with a steel wire brush, for fear of contamination.

Conversely, my (home made) conical anode on the propeller, gets almost none of the white coating, and consequently wears away much more evenly. What am I doing right?

subjecting your propeller anode to much higher water velocities, perhaps, and because it is in direct contact with a copper alloy component with a large surface area also subject to a much higher galvanic current density.

 

[smallplasticboat]

Hello - sorry to revive an old thread but I'm about to replace the anodes on my Yanmar 2YM20 with SD20 saildrive and flex-o-fold propellor ... that's three anodes (two on the SD and one on the prop) before even thinking about the two keel anodes on the boat (Jeanneau Sun Odyssey 319) as (a) they were in good shape last year and (b) I could not actually remove them! I am connected to shore power, if that is relevant.

Just wondering if I could save erosion on at least SOME of these rather expensive anodes by hanging a lump of zinc ( Milspec/U.S. Military Specification, A-18001K or otherwise) on a wire off the side of the boat, and connecting the wire to ... where? Presumably the saildrive? Will this have some awful effect elsewhere? Obviously I would have to keep a regular eye on the "conventional" anodes and replace them as required - just hoping to reduce the regularity!

 

[Tranona]

Hello - sorry to revive an old thread but I'm about to replace the anodes on my Yanmar 2YM20 with SD20 saildrive and flex-o-fold propellor ... that's three anodes (two on the SD and one on the prop) before even thinking about the two keel anodes on the boat (Jeanneau Sun Odyssey 319) as (a) they were in good shape last year and (b) I could not actually remove them! I am connected to shore power, if that is relevant.

Just wondering if I could save erosion on at least SOME of these rather expensive anodes by hanging a lump of zinc ( Milspec/U.S. Military Specification, A-18001K or otherwise) on a wire off the side of the boat, and connecting the wire to ... where? Presumably the saildrive? Will this have some awful effect elsewhere? Obviously I would have to keep a regular eye on the "conventional" anodes and replace them as required - just hoping to reduce the regularity!

A hanging anode has some uses mainly on boats that move in and out of fresh or brackish water where a magnesium anode is needed. So the mag anode is connected to the saildrive housing (not easy on some boats) when in fresh water.
However it will not do anything to reduce the erosion of the saildrive anode in seawater because the nature of galvanic action is that the closest anode erodes first. The hanging anode will not do anything until the saildrive anode is gone. It will not do anything for the prop anode for the same reason plus it cannot be connected direct to it. Remember a replacement saildrive is a £5k plus labour job and a Flexofold a minimum of £1k. So worth protecting properly.

The keel is a different story as generally anodes are not required on either iron or lead keels. They are essentially single metals so no chance of galvanic action. Corrosion on iron keels is straightforward rust - iron and water. However the iron used for boat keels is not pure and contains all sorts of bits of other metals that may set up a galvanic circuit. This will have no impact on the iron because of its mass but will erode a zinc anode. Generally speaking if you remove it you will not notice any difference. If you have a lifting keel the anode may be there to protect the lifting mechanism. If that is the case then a hanging anode will not make any difference unless it is directly connected to the metal it is intended to protect and hanging close by.