massive corrosion problem

[FourPoints]

Friends boat got short hauled today to inspect the sail drive and change a few seals that were due for replacement. It had been noticed a few weeks ago that there appeared to be a few drops of oil floating to the surface now and then... the pictures tell the story, sail drive is destroyed.

Question is how did this happen? The zinc isn't that old (9 months), and it didn't sacrifice, it instead turned to a thick white powder and everything around it has is the consistency of a sponge!

 

[thinwater]

More information please. And if it turned into a white powder, it did sacrifice and was not replaced soon enough. 9 months could be pretty old, depending. A year is just an average expectation.

• What was the material of the anode (zinc, aluminum, mag) and the brand?
• Where any other changes made to the boat (wiring, new marina)? Clearly something changed.

 

[Gunni]

The zinc metal surface salted up with zinc chloride, became insulated from the sea water and the more galvanically active aluminum case of the sail drive became the anode. Zinc would not be my choice for protecting an aluminum alloy saildrive. An aluminum anode would.

 

[Charles Erwin]

This is not galvanic. Your friend probably has a stray current problem. Obtain an assessment by someone local and qualified because - no matter what the underlying cause - this needs a definitive diagnosis and a fix.

Also your friend should alert his casualty insurer - possibly after he has gotten his independent report - because this is likely a covered event.

Charles

 

[alexco38]

Sorry.

Personally I am not a fan of sail drive or stern drive (power boat). Too much metal under water.

 

[Ted]

FourPoints: There was a very good article written about how to protect a sail drive in Cruising World. Some owners are not aware of how changes and upgrades that they make to their boat over the years will affect the corrosion protection of their zincs aluminum or magnesium anodes. Here is the link to that article.

http://www.cruisingworld.com/how/beware-unprotected-saildrive

 

[Crazy Dave Condon]

ON saildrives due to being aluminum, you cannot just put any antifouling paint on as it will inter react with the aluminum. Make sure the anti fouling paint says applicable to aluminum. That may be a cause but not sure.

 

[kloudie1]

One day, someone is going to wake up and start making a saildrive leg out of an engineered plastic like ULTEM http://www.ensinger-inc.com/products.cfm?page=product-sub-category&product=polyetherimide

Plenty strong enough and not susceptible to corrosion..
Probably not enough aftermarket yet for a replacement part, but would be MUCH better than cast aluminum..