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#1
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HELP: Zinc problem Volvo Sail Drive
claus wrote:
We have a Volvo MD22L engine equipped with a sail drive. The hull and prop are "supposed to be" protected with: 1) A Large Zinc block attached to the hull just forward of the sail drive and electrically connected to the engine block through the hull. 2) Round Zinc around the propellor shaft - attached to the sail drive 3) 3 small Zincs attached directly to the propellor The problem is that the 3 small zincs erode rapidly - sometimes within 2 months - and sometimes within 4 months...no regular pattern. The other zincs (1 and 2) look brand new after 2 years in the water and obviously do not protect the propellor at all. When the all the zincs were installed at the last haul-out 2 years ago I made sure they were free of any surface oxidation. I have also installed a Galvanic Isolator in an attempt to alleviate the problem - and the boat has been inspected for any stray currents and none found by the Marina staff. The boat next two ours is a derilict without any maintenance whatsoever - but is is also hoohed up to the same shorepower circuit as ours. The Marina staff dioes not think that is the culprit. Any suggestions? cvj Hello Claus, I'm on my way out, so just a brief post for now. First, it would not be surprising to find that the small zincs mounted on the prop go first. After all, they're right there. If everything is OK, then the other zincs will begin to work when the little ones are depleted. At this point, you can easily verify that the larger zincs are indeed connected electrically to the prop shaft and prop. Sometimes good contact is not made through shaft couplings, etc. and that would prevent the larger zincs from working. Of course the small ones on the prop are bonded electrically by definition. You can check the voltage between the engine ground and the prop side of the shaft. If you see nothing, even on the lowest DC voltage setting, chances are good they're bonded. Using an ohmmeter might be troublesome given the galvanic potentials that might be floating around. Good luck. Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#2
posted to rec.boats.cruising
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HELP: Zinc problem Volvo Sail Drive
One more quick thought. If you know the
approximate surface area of the prop and the weight of the zinc lost in say 2 months, it is fairly easy to figure out whether that is in the normal range. Let us know and we'll try to tell you. Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#3
posted to rec.boats.cruising
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HELP: Zinc problem Volvo Sail Drive
chuck wrote:
One more quick thought. If you know the approximate surface area of the prop and the weight of the zinc lost in say 2 months, it is fairly easy to figure out whether that is in the normal range. Let us know and we'll try to tell you. Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Yet another thought. If your larger zincs really do look "new" (i.e., they are shiny) then they are probably active. An inactive zinc usually looks dark and tends to acquire a film characteristic of submerged matter. Chuck |
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