I have had zincs put on by a commercial diver. They seem to last about three to four months at best. Bill I have an inverter which is almost always off wired to the battery switch. No to the stereo and bonded thru hulls. I have three bronze thru hulls and one marelon or whatever you call it. And the zincs are on the shaft. Yes to the SS shaft and bronze prop. Here's another queer fact. A guy was helping me with this and he tested my switch and said it was leaking current in the off position. So he put on a new (used) switch. Now bank 1 doesn't work at all. He claims it was working when he put it on. He's says he put all the wires back the way they were. He seems afraid to come back, knowing I'm not loaded with money. Don't know if there still is a leak, thus prompting my initial post.
I'm going to try putting on an actually new battery switch this weekend. I understand that there is no rush and it's probably better to test this with the boat in the water, but obviously I don't know enough yet. I'll try the method of disconnecting the batteries and running them through an ammeter?
Stephan,
1- One of the BIGGEST contributors to stray DC leaks is installers, yards and DIY's who think there is no difference between the boats GREEN/BONDING/EARTH wires and the DC BLACK/ NEGATIVE RETURN wires. There is a HUGE difference..
The green Earthing or bonding wires should always be at zero current/Earth potential. They are never intended to carry a DC or AC load unless there is a fault.
This is one of the most often violated "electrical blunders" I see on boats. Ask Roger Long about what he found last spring related to his "green" wires...
I have seen bilge pumps, water pumps, head shower sumps, fuel pumps, VHF's, mast wiring and just about every other sort of DC circuit you can imagine wired and using the BONDING/EARTH system as a DC negative return.
Start here and make sure there is not s sigle device in the DC system using the bonding/Earth system for a DC negative return to the battery.
Also the mast is NOT a DC current carrying device!!! I see this all the time too and the masts are bonded too turning the bonding/Earth grounds into DC current carrying wires.....
2- There should be a single Earth ground (NOT CURRENT CARRYING) and a single DC negative ground point for the entire boat. Multiple grounds are bad. These points are usually the engine block on boats with in-board engines. Try to keep all grounds on the engine to a single point as well then you minimize the engine being used to carry current other than the starter and alarm circuits. I always tend to add an extra ground wire, even on case grounded alts, that goes direct to the single point engine ground for a direct path back to the battery bank.
3- Cheap wire is another contributor. Many builders used trailer wire or worse, lamp cord. These wires can suffer from a phenomenon called "water treeing" where the jacket become a leak. Wire in the bilges are a big contributor.
4- If your boat DOES have a single "bonding/Earth" point you can remove this wire and insert a digital volt meter, set to DC amps on the mA setting first and the 10A setting next. You insert the meter between the main GREEN wire ground point and the piece it was bolted to. You then power up batt switch, on the mA setting, with NOTHING ON, and check for current flow in the bonding/grounding wires. The move to the 10A setting and turn on the DC devices one at a time being sure not to fire up motors until the very end of your test. DC motors for pumps, macerator etc. will often exceed the fast blow fuses inside the 10A DC amp circuit of the DVM. You are hoping NO DC devices are connected to the GREEN grounding wires and if they are you will see it here BUT only if your vessel does not have MULTIPLE ground points. If you see ANY current on any of the grounding/Earth wires this is BAD and needs to be corrected. DC current should only ever flow in the DC negative (BLACK or YELLOW) return wires.
5- Next insert your DVM on the mA setting between your battery positive post and the positive battery cable. With the switch off you should have no leakage/current unless you have a propane sniffer or other "always on" device. If you have current you need to disconnect circuits, one by one, until you find the offender.
All in all your zinc use is not crazy, should be better, and it could just be "cheap zincs". If you don't find anything doing the tests above install a
Godfrey Zinc on a CLEAN spot on the shaft and let us know how long you get.
This is what a "quality" zinc looks like. They DO NOT use a copper bearing to make shaft contact. Instead they utilize a completely embedded collar with about 1000+% more contact area to both zinc and shaft...
Note how even the wear is on this zinc:
Last summer I was pinched on time and did not have the ability to pick up a Godfrey zinc.
I used an el-cheapo copper bearing special... By July it was in pretty rough shape and unevenly erroded. Put on a good one in July and when the boat came out in late November it was still in near perfect shape... The quality of the zinc counts for a lot....
