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On Sun, 27 Jan 2008 18:22:55 -0800 (PST), Bil
wrote: Thanks for your responses. For Gordon: the RF ground/counterpoise is a copper foil which - I think - is connected to the engine block. For Chuck: I've not noticed the same erosion of the anode when in any of three different marinas and connected to shore power, including for months at a time. I've only noticed the erosion after passages that have included daily Pactor modem work. I renewed the shaft anode 3 months ago, found it erosion free 6 weeks ago before leaving a marina, and found significant pitting when I checked it two days ago after entering a marina (with 6 weeks of passage making and no shore power connection in between checks). Bil So we can rule out the shore power connection. I'd be inclined to rule out the HF rig as the culprit since from the perspective of galvanic currents it looks the same whether you are operating it or not. The HF rig would be a player only if you had a completely isolated DC ground system, in which your prop and shaft were not connected galvanically (by wire) to your DC ground. Such a system is rare on older boats but is beginning to appear on some new boats. As far as I know, there are no known cases of 150 watt radios accelerating zinc erosion via RF. The interesting variable in your situation appears to be the boat's motion. At rest in a marine, no problem. Underway, rapid erosion. Some of that erosion is simply due to the motion of the water relative to the prop. The faster you go, the faster the zinc will erode. Whether this could explain the problem depends on how long your passages were and how fast you were moving and past experience. Another possibility is that while underway, some piece of electrical equipment is energized that is off while you are at the marina. If this "appliance" is faulty, say with the positive wire shorting to the bilge water, you could be setting up a condition for accelerated erosion of your zinc. Next question might be how does your recent experience with zincs compare with previous passages? 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 =---- |
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