The acceleration of the zinc corrosion can be due to a number of things. The galvanic isolator can help if the marina has a grounding issue, and will fix that. Your problem is more likely due to dissimilar metals on your boat immersed in salt water. Many years ago I had a C&C 30 Mk I, and after 4-5 years of use, it started consuming several zincs in a season. I purchased a corrosion meter, made dozens of measurements, and realized it was due to the existence of the lead keel in combination with the lightning ground. At the end of the season, I had her hauled, stripped the keel paint, and barrier coat, replaced the barrier coat, the anti-fouling paint and never had another problem. If you think about it, a battery often is made of lead in combination with an electrolyte (eg, salt water) and other metals. By electrically connecting the lead keel and mast to the engine, shaft, zincs, thru hulls, etc, you have created a short-circuited battery, and accelerating the corrosion or the least noble of the metals—in this case the zinc. I was able to isolate the connections, and measure the open circuit voltage and the currents when shorted. Sure enough, the voltage was ~ 0. 5, and the current was ~ 100 ma. Not very much, but enough to eat away a zinc on 27/7 basis. My conclusion was that the barrier coat had isolated the keel for the early years, but after a while, it broke down, and exposed more lead to the sea thereby increasing the zinc cunsumption. It worked for me, and you might want to investigate.
Don Wagner previously C&C 30 owner, now, C&C 41CB DerBaron West River MD From: kelly petew via CnC-List Sent: Friday, April 27, 2018 6:00 PM To: cnc-list Cc: kelly petew Subject: Stus-List How many shaft zincs? I have always installed two [2] shaft zincs, at the beginning of sailing season. For last two seasons, I've seen their deterioration accelerate in my marina, despite having a galvanic isolator on board. I know I need to find the stray current source. That said, any thoughts on adding a third zinc as a measure of "insurance"? thanks, Pete W. Siren Song C&C30mkII Deltaville, Va. -------------------------------------------------------------------------------- _______________________________________________ Thanks everyone for supporting this list with your contributions. Each and every one is greatly appreciated. If you want to support the list - use PayPal to send contribution -- https://www.paypal.me/stumurray
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