Do you need to zinc your bronze rudder hinges? - SailNet Community
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post #1 of 3 Old 08-12-2012 Thread Starter
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Do you need to zinc your bronze rudder hinges?

I currently have an overly-exotic zinc system that came with the boat. I believe it is designed under the trade name "diver's nightmare!" and I've been the diver!

Next haul out I plan to re-do the whole thing. What I am wondering is if I really need to zinc my bronze rudder hinges? I don't believe in bonding every through hull and there are several silicone bronze through hulls that aren't directly connected to zinc and have been doing just fine. Why then, is there a huge plate zinc on my hull with a wire that attaches to the bronze hinges?

I know that a bronze prop can get eaten, thus the shaft collar zinc. Through hulls don't seem to get eaten. Is that because they're more isolated from the metals of the engine? The hinges seem to be more like the isolated through hulls to me.... Also, I don't recall seeing sacrificial zincs, or easy places designed into boats for said zincs, in the masses of boats in the yards.

Do you have zinc protecting your rudder hinges? Do I need it?


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post #2 of 3 Old 08-12-2012
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I think it's a good idea. I usually sand them to metal leaving the bits where the paint is really stuck and prime with E2000 or equivalent epoxy primer then use a good quality bottom paint. The only thing I don't paint is the wheel (prop) and shaft.
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post #3 of 3 Old 08-12-2012
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Re: Do you need to zinc your bronze rudder hinges?

You definitely need anodic protection for 'any' underwater metal ... either by a zinc affixed to the component or bonding it to a common 'zinc' through electrically intact wiring.

Formosa boats and other typical Taiwanese boats of that era usually had the bronze rudder pintles/hinges bonded to the rudder zinc through a copper 'strap' that was buried in the fiberglass of the aperture. You can check to see if this electrical protective circuit is still intact by using a voltmeter (VOM) between the cutless housing and the 'hinges' ...
AND the imbedded rudder frame if exposed. Since the cutless housing is usually connected to the boat's bonding system .... any zinc connected (and still electrically intact) should provide the pathway to 'any' so attached anode.
The problem here is not of 'over zinc' the boat ... or you will pick up a lot of hard growth such as barnacles on the prop, and other underwater metal running gear. For such a large boat you really ought to be using a calibrated 'reference' cell to measure the potential requierments of any large boat ... and apply the correct amount of anode surface area in accordance to the cell readings ... too little protection and you will begin to extract zinc from 'castings', etc., too much protection and all the underwater gear will become fouled with hard growth.

Corrosion reference cell/electrode: Corrosion Reference Electrode
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