Thursday, November 26, 2009


Journeyman's beautiful propeller has two zincs, and I am pretty careful about keeping them renewed. As anyone reading this likely knows, dissimilar metals near each other and submerged in an electrolyte (e.g., seawater) form an electric circuit. Ions (dissolved metals) from the "more noble" metal migrate to the "less noble" metal. This statement approximately exhausts my knowledge of electrolysis, but it is about all I need to know: if I have a zinc on my bronze prop, the zinc erodes instead of the prop. But if the zinc is all gone, or if I bolted the zinc onto a greasy shaft, the circuit forms between the steel propeller shaft and the prop, and the prop erodes . . .

Bronze that has been subject to electrolysis takes on a reddish hue. Pitting may appear, and metal may be gone from thin edges.

The first few years I owned Journeyman I had a problem with shaft zincs loosening through vibration. A trick prevents this. Tighten the zinc over a nice clean shaft. Then tap the zinc firmly all over with a hammer, re-tighten, and repeat. I usually back up the hammer with a sledge held against the zinc, so I won't punish the shaft.

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