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Nothing happens without the wire ;) From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Della Barba, Joe via CnC-List Sent: Tuesday, October 02, 2018 8:19 AM To: cnc-list@cnc-list.com Cc: Della Barba, Joe <joe.della.ba...@ssa.gov> Subject: Re: Stus-List [EXTERNAL] Re: Prop shaft zincs, bonding and corrosion A couple of points: 1. A zinc only protects things it is electrically connected to. This means it does protect the shaft and prop for sure. The engine and anything wired to the engine – maybe. If you think about it, there should be no such thing as metal to metal contact between a rotating shaft and a stationary engine. Everything that turns passes through bearings and seals, so the electrical connection more or less depends on the oil settling with the engine off and the crankshaft resting on a bearing. This is why commercial vessels have a carbon brush arrangement or other ways to connect to the shaft. 2. Measuring voltage between things can be confusing. Any two metals that are not the same alloy in salt(ish) water make a battery *if connected*. So if you have a bronze thu-hull and a stainless shaft, you will see voltage between them. If they are connected electrically, one will corrode. This is why they both would also need to be connected to a zinc so the zinc is what corrodes. Absent wiring between them, they should both just sit there, there is no current path. If two metals are connected by a bonding wire, you would end up measuring 0 volts between them. That is NOT good, that means the bonding wire is carrying the current and one of those two metals is corroding. Only good outcome is if one of the two is a zinc. 3. The two choices are isolate everything, which is what I do, or connect everything and make sure it is all wired to a zinc. The prop shaft zinc is marginal for this job at best. Standard big powerboat setup is bonding wires everywhere and a big hull zinc besides for the prop shaft zincs. 4. Connecting to shore power absent isolation now connects you to all kinds of underwater metal. The very best outcome is you eat up your neighbor’s zincs, but probably the reverse is what really happens, never mind some wiring malfunction that sets up current between boats. Joe Coquina C&C 35 MK I From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Josh Muckley via CnC-List Sent: Tuesday, October 02, 2018 5:34 AM To: cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com> Cc: Josh Muckley <muckl...@gmail.com<mailto:muckl...@gmail.com>> Subject: [EXTERNAL] Re: Stus-List Prop shaft zincs, bonding and corrosion I've had difficulty finding the "correct" answer regarding "What are the shaft and prop zincs protecting?" Most people agree that they protect the shaft and the prop, but what about the engine or the other metal through hulls? What about the keel, and mast? I installed a shaft coupler isolator (for vibration dampening) which suggested a jumper wire across the coupler "if needed" to restore electrical continuity between the engine and the shaft. I've repeatedly asked various resources, "When would it be needed?" with no consensus and little or no scientific or regulatory explanation either way. I don't currently have a jumper installed. I'm quite confident that I my anodes protect exactly what they are supposed to protect, the shaft and the prop and nothing else. If I were you, I would disconnect various ground and bonding paths and measure the voltages across the connection. There is really only one acceptable reading. 0.00 volts. Anything else means that current is passing through that particular ground/bonding wire to the bonded item and then through the water around the boat to another underwater item. Check for both AC and DC volts. You might start with the shore power ground wire. Easy as unplugging and then check voltage between the outlet ground and the plug. Then move to the shaft ground brush. Then separate your shaft coupling. Each step looking for volts across the newly disconnected pieces. That should prove or disprove a stray current problem. If current is found then reconnect and move down the line until you isolate the problem to a sub-circuit or component. Remember there are unexpected ground connections in waterheaters, computers, microwaves, battery chargers, inverters, TVs, antennas, light fixtures and pumps. Pretty much anything with a metal case mounted with metal screws, or interconnected to anything else besides power. If no current problem is found then consider using larger anodes, more of them, or less active anodes. Good luck, Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD
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