Anode question

[eddystone]

Thanks to this forum I am now aware that if your mooring is in brackish water you should have aluminium rather than zinc anodes. However i also understand all anodes should be the same material. I have recently fitted a Featherstream prop and they don't yet supply aluminium anodes so the only way to have prop, shaft and hull anodes all the same is to use zinc. I wonder which is better, aĺl zinc or change hull and shaft only to aluminium? I've been moored in brackish water for 6 years and although i do get heavy deposits on the hull anode which i guess stops iit working I haven't seen any ill effects.
Also saw something about bonding system needing to protect s/s rudder shaft and tangs but no idea how you would do that

 

[RichardS]

I can't see what harm it would do to have zinc and aluminium anodes fitted at the same time provided that they are not right next to each other. You could therefore use the zinc prop anode until such time as an ally one becomes available.

Richard

 

[VicS]

Thanks to this forum I am now aware that if your mooring is in brackish water you should have aluminium rather than zinc anodes. However i also understand all anodes should be the same material. I have recently fitted a Featherstream prop and they don't yet supply aluminium anodes so the only way to have prop, shaft and hull anodes all the same is to use zinc. I wonder which is better, aĺl zinc or change hull and shaft only to aluminium? I've been moored in brackish water for 6 years and although i do get heavy deposits on the hull anode which i guess stops iit working I haven't seen any ill effects.
Also saw something about bonding system needing to protect s/s rudder shaft and tangs but no idea how you would do that

The reason why zinc and aluminium anodes are not mixed on the same system is that aluminium anodes are slightly more anodic than zinc anodes. If the two are mixed the aluminum anode(s) will do all the work and the zinc anode(s) little or nothing.
You dont say what your hull anode is bonded to and fitted to protect. Originally just the old fixed blade prop ? If so, and any flexible shaft coupling is bridged to enable it to do this I think I would change the hull anode to aluminium. At least it will offer some protection to the prop when its own anode has become ineffective due to being moored in brackish water.
I would also change the shaft anode to aluminium as this will give better protection of the prop than the hull anode.

The zinc prop anode will end up doing nothing. At least it should not need changing very often.

Would be a good idea to ask Darglow for advice, running the above thinking before them.

Maybe Vyv Cox will have some thoughts on the matter.

 

[vyv_cox]

I think Vic has covered it. All the anode companies are promoting aluminium alloy anodes as the first choice nowadays, regardless of water salinity. But, as you have noted, specialist anodes are not yet available in the aluminium alloy. You might consider an additional aluminium alloy anode on a cable over the side when berthed, with the connection made to the prop shaft, plus an aluminium shaft anode.. You could then retain the zinc prop anode but have protection provided for the majority of time by the aluminium ones. Hopefully the prop manufacturers will offer aluminium anodes before too long, as I am in the same position with Brunton.

 

[RichardS]

I can't see what harm it would do to have zinc and aluminium anodes fitted at the same time provided that they are not right next to each other. You could therefore use the zinc prop anode until such time as an ally one becomes available.

Richard

 

[VicS]

I can't see what harm it would do to have zinc and aluminium anodes fitted at the same time provided that they are not right next to each other. You could therefore use the zinc prop anode until such time as an ally one becomes available.

Richard

You already said that in #2 .

 

[eddystone]

The reason why zinc and aluminium anodes are not mixed on the same system is that aluminium anodes are slightly more anodic than zinc anodes. If the two are mixed the aluminum anode(s) will do all the work and the zinc anode(s) little or nothing.
You dont say what your hull anode is bonded to and fitted to protect. Originally just the old fixed blade prop ? If so, and any flexible shaft coupling is bridged to enable it to do this I think I would change the hull anode to aluminium. At least it will offer some protection to the prop when its own anode has become ineffective due to being moored in brackish water.
I would also change the shaft anode to aluminium as this will give better protection of the prop than the hull anode.

The zinc prop anode will end up doing nothing. At least it should not need changing very often.

Would be a good idea to ask Darglow for advice, running the above thinking before them.

Maybe Vyv Cox will have some thoughts on the matter.

I have a very sketchy understanding of what anodes are meant to do but the hull anode is wired to the engine block (i think) and the P bracket. Previous advice from multiple sources was not to bother bonding in seacocks. I will ask Darglow about effect of aluminium anode on prop

 

[VicS]

I have a very sketchy understanding of what anodes are meant to do but the hull anode is wired to the engine block (i think) and the P bracket. Previous advice from multiple sources was not to bother bonding in seacocks. I will ask Darglow about effect of aluminium anode on prop

The hull anode connected to the engine block will protect the prop provided any flexible coupling is bridged so that there is a good electrical connection from the anode to the prop..

the P bracket is unlikely to need protection from an anode.

Modern advice is definitely not to bond seacocks etc to the anodes. They should be made of materials, eg plastic, bronze or DZR brass, which are corrosion resistant.

MG Duff explain "galvanic" corrosion and the principles of cathodic protection by sacrificial anodes on their website.

http://mgduff.co.uk/cathodic-protection

 

[eddystone]

The hull anode connected to the engine block will protect the prop provided any flexible coupling is bridged so that there is a good electrical connection from the anode to the prop..

the P bracket is unlikely to need protection from an anode.

Modern advice is definitely not to bond seacocks etc to the anodes. They should be made of materials, eg plastic, bronze or DZR brass, which are corrosion resistant.

MG Duff explain "galvanic" corrosion and the principles of cathodic protection by sacrificial anodes on their website.

http://mgduff.co.uk/cathodic-protection

Thanks for information