Only three things made of metal project through my hull. The shaft, the rudder post, and the lead keel. No bonding wires on the Marlon through hulls. Arguably the internals of the engine and A/C could be in contact via the cooling water and electrical ground paths.
Someone else tried to convince me that without an adequate ground path to the water that it was a shock hazard for nearby swimmers. Josh On Tue, Oct 2, 2018, 11:07 AM Della Barba, Joe via CnC-List < cnc-list@cnc-list.com> wrote: > If you want to protect metal, you need to connect it to a zinc somehow. > Adding that jumper will connect the shaft zinc – sort of – to the engine > which is connected to ground. You would have to measure the resistance from > the engine negative connection to the shaft to see how well thiwould work. > If your vessel has bonding connections, you absolutely need this jumper! If > not, probably not. > > Joe > > Coquina > > > > *From:* CnC-List [mailto:cnc-list-boun...@cnc-list.com] *On Behalf Of *Josh > Muckley via CnC-List > *Sent:* Tuesday, October 02, 2018 11:00 AM > *To:* C&C List <cnc-list@cnc-list.com> > *Cc:* Josh Muckley <muckl...@gmail.com> > *Subject:* Re: Stus-List [EXTERNAL] Re: Prop shaft zincs, bonding and > corrosion > > > > 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 > > _______________________________________________ > > 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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