Bronze vs. Stainless Shafts and Marine Growth

[Sabreman]

For many years I've has bronze shafts. We keep our boat(s) on the Chesapeake and by July there are a fair number of barnacles on the shaft and prop. Last year, I replaced the shaft with one of stainless steel. I swear that the new shaft accumulates less growth than the old one. Since I kept the old bronze prop, I was able to compare the growth and it really looked like it had more growth

Questions:
1. Has anyone else experienced reduced growth on stainless (or is it my imagination?
2. Why would bronze allow any growth at all considering it is "..at least 89% copper..."? My bottom paint has less copper and barely anything grows on our (boat) bottom. I know that paints have additives, but the active ingredient is copper. See the related link:
Silicon Bronze - Mechanical Engineering, Mechanical Engineer, Material Engineer, Material Engineering,Manucaturing Engineering

[Fstbttms]

Originally Posted by Sabreman

2. Why would bronze allow any growth at all considering it is "..at least 89% copper..."? My bottom paint has less copper and barely anything grows on our (boat) bottom. I know that paints have additives, but the active ingredient is copper.

Copper-laden anti fouling paints work by constantly leaching biocide (cuprous oxide), thereby retarding the growth of organisims. A bronze prop shaft does not do this. It is a good question however. Some boats still use copper sheathing as an effective anti fouling solution.

[T37Chef]

Sabreman is certainly right about the bad season last year in the Chesapeake with alga growth and barnacles. When pulling the boat two weeks ago I found out how bad it was, in fact I am not sure the Auto stream prop would have worked with so much build up. I have applied a zinc paint by Interlux in hopes that it will reduce the problem to a minimum?

Has anyone had good results with something else?

[Sabreman]

Good thought, Fstbttms. If the shaft constantly leeched copper, there would be nothing left to it after a while. I suppose the silicon that is added to the bronze really hardnes it.

[sailingdog]

I know some people coat the prop with either anhydrous lanolin or Lanocote... I don't know how well it works though... You could also try to coat it with some of the new dry film lubricants, like McLube SailCote... and see if that helps.