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I don't know for sure if it can be used on a sail drive. On the can's label it says, "Zinc Coat Barnacle Barrier - Protects Underwater Metals." On the back it says it contains 93% pure zinc. It says "This product is for use only on bare metals, such as steel, stainless steel, cast iron, copper, bronze, galvanized iron and lead." If in doubt, I'd suggest you email Petit at their website.
It sounds like it works just like the zinc anode on your prop shaft. If you spray it on the shaft, it slowly erodes. A barnacle can't attach itself to it, because the thin layer of zinc erodes out from under it.