Anodes

[Sailfree]

Has anyone tried melting down the remaining Zinc anode and recast them as the simple teardrop anode.

I always berth my boat easy slotting it astern into a gap on 2' wider than my beam but sheltered by a old scottish (now livaboard) trawler with long bowsprit. After cleaning bowthruster tunnel and bowthruster propellers and main propeller had real difficulty having to adjust to such a responsive boat!

Replaced mine yesterday on a simple lift and hold for 5hrs. We were asked to stop pressure washing the boat as they were filming a documentary on McNamara the surfer who surfed the 100' wave in Nazare (spectacular see it on YouTube).

We explained we had a time constraint and they kindly moved their filming elsewhere.

 

[macd]

Has anyone tried melting down the remaining Zinc anode and recast them as the simple teardrop anode.

Several forumites have certainly considered it and I seem to remember a few have done it. A search should reveal more.

 

[VicS]

Has anyone tried melting down the remaining Zinc anode and recast them as the simple teardrop anode.

I always berth my boat easy slotting it astern into a gap on 2' wider than my beam but sheltered by a old scottish (now livaboard) trawler with long bowsprit. After cleaning bowthruster tunnel and bowthruster propellers and main propeller had real difficulty having to adjust to such a responsive boat!

Replaced mine yesterday on a simple lift and hold for 5hrs. We were asked to stop pressure washing the boat as they were filming a documentary on McNamara the surfer who surfed the 100' wave in Nazare (spectacular see it on YouTube).

We explained we had a time constraint and they kindly moved their filming elsewhere.

If you try this bear in mind that the zinc used for anodes is a special high purity grade with a few small additions made to a US Military specification

Be very careful to avoid contamination with even minute amounts of copper, lead and especially iron or the resulting anodes may not be effective ( max concentration of these elements is 0.005%)

A little bit of background info:

The current U.S. Military Specification, A-18001K, is the result of work carried out by scientists for more than five decades. Before the mid 1950s, corrosion prevention was not fully understood with dramatically different results from similar vessels treated with apparently the same Zinc Anode protection.

Investigations into why only some of these vessels suffered from extensive corrosion indicated that some Anodes became passivated when a white crust formed on their surface . The crust was tested as Oxides of Iron and was determined to have been caused by excessive impurities in the product, mainly Iron. The formation of the crust made the Anodes inactive allowing corrosion to take place elsewhere in the vessel.

The first US military specification resulted, which limited the number of impurities in the Zinc used, resulting in the requirement to use high grade Zinc and strict manufacturing practices.

The specification has been refined over the years with the result that modern anodes manufactured to the specification should remain active throughout there lives by producing a thin zinc oxide film which will easily slough off.​

 

[Sailfree]

If you try this bear in mind that the zinc used for anodes is a special high purity grade with a few small additions made to a US Military specification

Be very careful to avoid contamination with even minute amounts of copper, lead and especially iron or the resulting anodes may not be effective ( max concentration of these elements is 0.005%)

A little bit of background info:

The current U.S. Military Specification, A-18001K, is the result of work carried out by scientists for more than five decades. Before the mid 1950s, corrosion prevention was not fully understood with dramatically different results from similar vessels treated with apparently the same Zinc Anode protection.

Investigations into why only some of these vessels suffered from extensive corrosion indicated that some Anodes became passivated when a white crust formed on their surface . The crust was tested as Oxides of Iron and was determined to have been caused by excessive impurities in the product, mainly Iron. The formation of the crust made the Anodes inactive allowing corrosion to take place elsewhere in the vessel.

The first US military specification resulted, which limited the number of impurities in the Zinc used, resulting in the requirement to use high grade Zinc and strict manufacturing practices.

The specification has been refined over the years with the result that modern anodes manufactured to the specification should remain active throughout there lives by producing a thin zinc oxide film which will easily slough off.​

Interesting. The Variprop Anode (supplied by Variprop) is never eaten away very much and has a grey crust. The Shaft Anode supplied by MG Duff is always eaten away (interesting this time one side hardly touched the other side severely eaten away - one side not woking?) . Are variprop supplying less than perfect anodes to increase future prop sales?

 

[Daydream believer]

I certainly intend to do it. I will be building a small forge later this winter & I have saved 16 years of anodes. Please do not tell me that those highly expensive Brunton anodes cannot be re formed. Same for the Volvo saildrive ones. :ambivalence:

 

[NormanS]

Has anyone tried melting down the remaining Zinc anode and recast them as the simple teardrop anode.

I always berth my boat easy slotting it astern into a gap on 2' wider than my beam but sheltered by a old scottish (now livaboard) trawler with long bowsprit. After cleaning bowthruster tunnel and bowthruster propellers and main propeller had real difficulty having to adjust to such a responsive boat!

Replaced mine yesterday on a simple lift and hold for 5hrs. We were asked to stop pressure washing the boat as they were filming a documentary on McNamara the surfer who surfed the 100' wave in Nazare (spectacular see it on YouTube).

We explained we had a time constraint and they kindly moved their filming elsewhere.

Yes, I melt down the zinc from old anodes to make one for my Bruntons Autoprop, each year. I hear all the naysayers who claim that the zinc must be of almost unbelievable purity, and laugh in their faces. An anode is designed to be of a less noble metal than the one(s) that it is there to protect, and in the process it erodes away, so it hardly matters if there is a bit of impurity in it. Obviously, when the zinc is molten, any obvious dirt or scum can be easily skimmed off, before pouring into the mould. My anodes behave just the same as the expensive proprietary ones. Go for it.

 

[vyv_cox]

Vic's post spells it all out. You need to limit iron as much as possible. Cut any steel straps off before melting, don't just chuck the whole anode in the kiln. Use a ceramic crucible.

 

[NormanS]

Vic's post spells it all out. You need to limit iron as much as possible. Cut any steel straps off before melting, don't just chuck the whole anode in the kiln. Use a ceramic crucible.

It's much easier just to fish out bits of steel straps once the zinc has melted off. I melt (and pour) using an iron ladle, which was formerly used for paying seams on traditional wooden decks. But if you're determined to spend money, buy your anodes.

 

[VicS]

Interesting. The Variprop Anode (supplied by Variprop) is never eaten away very much and has a grey crust. The Shaft Anode supplied by MG Duff is always eaten away (interesting this time one side hardly touched the other side severely eaten away - one side not woking?) . Are variprop supplying less than perfect anodes to increase future prop sales?

I would be very suspicious of an anode on a nickel aluminium bronze propeller which is not eaten away.

EDIT;
There is between 0,8 and 0.9 volt between them in the galvanic series which says that a zinc anode will be eaten away if there is good electrical contact with the prop.

A grey crust suggests that it is becoming passivated.. Check the electrical connection but also be sure to maintain your shaft anode.

 

[Sailfree]

I would be very suspicious of an anode on a nickel aluminium bronze propeller which is not eaten away.

EDIT;
There is between 0,8 and 0.9 volt between them in the galvanic series which says that a zinc anode will be eaten away if there is good electrical contact with the prop.

A grey crust suggests that it is becoming passivated.. Check the electrical connection but also be sure to maintain your shaft anode.

I always check continuity after fitting every anode including bow thruster but Prop anode is rarely eaten away just surface while the shaft anode some 300mm back (P bracket in the way!) is always about 50% of original weight.

 

[vyv_cox]

It's much easier just to fish out bits of steel straps once the zinc has melted off. I melt (and pour) using an iron ladle, which was formerly used for paying seams on traditional wooden decks. But if you're determined to spend money, buy your anodes.

I paint my prop with Hammerite and Velox instead, to reduce the cathode area and eliminate fouling. My Bruntons anode easily does two seasons, would probably do three. The shaft anode does four and was only half gone then but I thought it deserved to be replaced.

 

[davidwf]

Yanmar use an Aluminium anode on their sail drive legs, and jolly expensive they are too. I am always puzzled as to why they don't use Zinc. ASAP have zinc ones that are about half the price of the Yanmar aluminium ones. The Yanmar ones hardly corrode at all , Brunton varifold ones do and need changing halfway through the season. Perhaps they are protecting the sail drive aluminium ones.

 

[Daydream believer]

My Brunton anode has to be changed mid season. The volvo 120 saildrive one does a season & "may" do 2 short seasons, but I have a rope cutter & there would be gaps behind it & so I prefer to change the anode

 

[VicS]

Yanmar use an Aluminium anode on their sail drive legs, and jolly expensive they are too. I am always puzzled as to why they don't use Zinc. ASAP have zinc ones that are about half the price of the Yanmar aluminium ones. The Yanmar ones hardly corrode at all , Brunton varifold ones do and need changing halfway through the season. Perhaps they are protecting the sail drive aluminium ones.

Aluminium and zinc anodes should not be mixed on the same system. If they are then the aluminium anodes will protect the zinc ones and be consumed preferentially. However saildrive props are electrically insulated from the shaft and the rest of the saildrive consequently there should be no interaction between the prop anode and the saildrive leg anode

 

[NormanS]

I paint my prop with Hammerite and Velox instead, to reduce the cathode area and eliminate fouling. My Bruntons anode easily does two seasons, would probably do three. The shaft anode does four and was only half gone then but I thought it deserved to be replaced.

That makes sense.

 

[Daydream believer]

Aluminium and zinc anodes should not be mixed on the same system. If they are then the aluminium anodes will protect the zinc ones and be consumed preferentially. However saildrive props are electrically insulated from the shaft and the rest of the saildrive consequently there should be no interaction between the prop anode and the saildrive leg anode

I should raise a point here. They are not insulated if one has an ambassador rope cutter & a Brunton Auto prop. I suspect it applies to other props as well.

 

[VicS]

I should raise a point here. They are not insulated if one has an ambassador rope cutter & a Brunton Auto prop. I suspect it applies to other props as well.

If the electrical isolation of the prop is compromised it will become a major galvanic corrosion threat to the sail drive leg.
The sail drive anode will have a much shortened life. Probably to only a few months, necessitating more frequent, and more important, inspection and replacement

 

[Daydream believer]

If the electrical isolation of the prop is compromised it will become a major galvanic corrosion threat to the sail drive leg.
The sail drive anode will have a much shortened life. Probably to only a few months, necessitating more frequent, and more important, inspection and replacement

See my post #13
But thinking about it further, I could drill the locating holes that drive the cutter pins a bit bigger. Upon doing that I could put plastic rings around the drive pins so they do not actually touch the brass back plate. the plastic rings will not split because they could be made with a tight fit in the drive holes. Then a .2mm Th plastic shim between cutter face & prop face would complete the insulation.
The alternative would be to remake the cutter ( I made this one as a copy of the Ambassador) & put a thin plastic sheave on the shaft between main SS part of the cutter so that the cutter was isolated from the shaft.
That would be a big improvement on the Ambassador design.

 

[VicS]

See my post #13
But thinking about it further, I could drill the locating holes that drive the cutter pins a bit bigger. Upon doing that I could put plastic rings around the drive pins so they do not actually touch the brass back plate. the plastic rings will not split because they could be made with a tight fit in the drive holes. Then a .2mm Th plastic shim between cutter face & prop face would complete the insulation.
The alternative would be to remake the cutter ( I made this one as a copy of the Ambassador) & put a thin plastic sheave on the shaft between main SS part of the cutter so that the cutter was isolated from the shaft.
That would be a big improvement on the Ambassador design.

The Ambassador should be Ok

ITYWF that its Delrin bearing will preserve the electrical isolation of the propeller.

 

[[70521]]

Has anyone tried melting down the remaining Zinc anode and recast them as the simple teardrop anode.

Its a lot cheaper just buying a new anode.