So Joe, you've joined me on the dark side! You've isolated everything. My question still remains, When is the jumper needed?
Josh On Tue, Oct 2, 2018, 8:19 AM Della Barba, Joe via CnC-List < cnc-list@cnc-list.com> wrote: > 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 > *Cc:* Josh Muckley <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 > _______________________________________________ > > 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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