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Old 02-03-2017, 12:59 PM   #9
psneeld's Avatar
City: AICW
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 20,336
The is no harm in putting copper bottom paint on bronze or stainless underwater gear. I have seen countless prop and rudders painted my whole life with no issues. My own included.

It's not the best way to paint them...but there is no harm.

But definitely not on aluminum.

Larsen Marine | Yacht Sales, Service, Storage | Waukegan, IL - Applying Bottom Paint

Antifouling paint should not be applied over a topside finish.
Propellers, outboards and outdrives are constructed of aluminum, stainless steel or bronze. There are no reaction problems in using paints containing cuprous oxide on stainless steel or bronze.
Care should be taken not to paint zinc anodes, which are often located next to the prop shafts, as this will seriously reduce their effectiveness.
When painting your outdrives, underwater metals and keels, the longevity of any antifouling is difficult to predict, as the coating adhesion is an issue, particularly on propellers, due to the harsh treatment these areas receive. (978-841-9978) - FAQs

Answer T2: There are two dimensions to this topic.
First, the larger the surface area of an anode, the higher its electrical current capacity and galvanic holding voltage. For most boats, you want your anode surface area to be sufficient to maintain all underwater metals between -900 mV and -1100 mV relative to a silver/silver-chloride reference electrode.

Second, the longevity of a sacrificial anode is a function of its weight -- the greater the weight the longer its life.

Due to differences in water salinity, temperature, stray currents, and other external influences, you only know the right weight by actual trial. Periodically inspect your zincs, and when they have corroded to under 50% their original weight they should be replaced. To lengthen the replacement interval, increase the weight of zincs used.

If you have a steel or aluminum hull vessel that operates in salt water, use our Calculation Formula and/or give us a call. We've designed hundreds of corrosion protection solutions for metal boats and underwater metal structures such as docks, boat lifts, and retaining walls.
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