Copper Antifouling Issues

[caribcat]

I manage a cat in Palma that has recently been coppercoated. About six months later we noticed that we had a leaking elbow, looking further we think that most of the elbows above thru-hulls are becoming fragile. Diving over the side we can see a light circular area around each skin fitting.

We think that the zinc used to strengthen the bronze is being drawn out of the elbows by the copper. Is this possible? Coppercoat had no explaination for this.

We came across some historical documents showing how once timber ships had been sheeved in copper, the galvanising disappeared from the nails leading them to rot.

in addition, we can get a continuity reading between 2 thru hulls, even though Coppercoat quoting the rather weak Branleys law say this is impossible.

Anybody shed any light on this for me?

Tom

[Astrid]

Proper Bronze is an alloy of Tin and copper, sometimes with silicon, phosphorus, aluminium, or manganese. Brass is an alloy of copper and zinc and probably should not be used for marine applications. So if your fittings are brass instead of bronze, there may be problem if the fittings are not bonded, but I am not so sure the copper coat has much to do with that, but anything is possible.

By the way, the cure for the corroding action between coated iron nails and copper sheathing on wooden ships you noted, was eventually cured by use of copper nails instead of tinned iron nails.