Anodes

[mikehhogg]

POLY you go ahead and use graphite all you like but chemistry is chemistry and where aluminium is concerned graphite will accelerate the corrosion process. you don't have to be connected to shore power to be affected by stray currents in a marina,you just have to be tied up in there.Another thing I see people doing is using copper based antifoul on their boats ,yet again another accelerator in the corrosion process.The proof as I stated earlier is my fifty year old all aluminium de groot that has no traces of corrosion.Zincs from new and plenty of them, cleaned anodes regularly and kept as far away from Marinas as possible

[Poly]

Originally Posted by mikehhogg

POLY you go ahead and use graphite all you like but chemistry is chemistry and where aluminium is concerned graphite will accelerate the corrosion process. you don't have to be connected to shore power to be affected by stray currents in a marina,you just have to be tied up in there.Another thing I see people doing is using copper based antifoul on their boats ,yet again another accelerator in the corrosion process.The proof as I stated earlier is my fifty year old all aluminium de groot that has no traces of corrosion.Zincs from new and plenty of them, cleaned anodes regularly and kept as far away from Marinas as possible

If science is your argument you’ll need more than n=1 with no reference study to prove your point!

Graphite can only “accelerate*” the corrosion process if both the graphite and the anodic material are both immersed in the sea water and electrically connected. It’s as misleading to say that graphite (especially graphite encapsulated in a hydrophobic grease) is about to be the death of any boat as it would be to suggest that wiring on boats should not contain copper! (Or indeed gold plated electrical contacts)

There are theoretical ways that stray currents could affect your boat without being connected to shore power but they are somewhat odd situations and even less likely to happen on a typical rib installation (which won’t have metallic through hull skin fittings).

*accelerate is probably a misleading term here since the rate is proportional to the surface areas of the anode and cathode, the distance between them as well as the potential of the materials. In many cases changing materials will not result in a significant rate difference - because the other factors dominate. In a perfect storm such as direct contact between aluminium and graphite whilst under water could...

[mikehhogg]

POLY I have no intentions of going tit for tat here but the proof you so desire is found in the fact that I have never suffered corrosion on a fifty year old hull , no corrosion on volvo penta outdrives,props etc because I researched the topic. Mercruisers reason for changing to aluminium may be linked to the fact that at one point aluminium was three times cheaper "CHEAPER" being the key word here. If a copper coin sitting on the hull of an aluminium boat in sea water can make a hole in the hull with the water on the outside of the hull where is your theory of immersion.you don't need wires connecting all these things together.
Close proximity in damp conditions will do the damage.If anodes are being eroded in six months then there is something seriously wrong eg use of wrong anodes use of copper based anti foul or just stray currents flowing all over the place. I am resting my case but my money is on Zinc.