electrical system gone to ground...

[Dick McKee]

I posted this same question on the big boat board, but would sincerely appreciate suggestions from the entrie community. We were recently notified by our divers that our 95 430 has began to eat up zinks. The prop shaft zink usually lasts about 4 months, but the most recent one went in a little under a month. We have added nothing or changed anything on the boat. She is equiped with 30 amp shore power. Heart 2000 inverter/charger, 3 isolated battery banks (2 house banks 8Ds and 1 starter bank with solar pannel). When we leave everything is shut off except the inverter/charger and the auto bilge pump. I plan to start with the standard cheapo pump float switch, then the pump and then inverter/charger. Any ideas?? I've also been told that other boats in the marina (about 530) can be the source of the prob.. How do I check this out?? And finally, although I'm very mechanical and truely enjoy working on the boat ( I know I'm sick), is this the kind of problem I should hire a professional to sort out?? Thanks in advance.Dick McKeeS/V Constellation.

 

[Gordon Myers]

Quick Solution

Leave the boat with the shore power cord DISCONNECTED. You will not be charging the batteries but will be preventing the electrical connection between your boat and all the other boats in your marina via the common wiring in the marina's electrical system. I would also install 2 or 3 shaft zinc's PLUS hang an additional zinc source in the water connected to your boats grounding system. This could be your drive shaft (inside), keel bolt, standing rigging, grounding bar, ect.The problem is probably in someone else's boat, but it is next to impossible to find. If you must leave your shore power connect when away from your boat then do the above to slow the problem on your boat and hire a professional to investigate.Good Luck. & Have a Happy New Year..

 

[Rick]

Disappearing Zincs

Installing additional zincs is not a good solution to the problem. The stray current will disolve the zincs and leave a plating of zinc oxide on your prop and shaft that will degrade performance just like bottom growth - but alot harder to scrape off.For a full discourse on stray currents that eat zincs, check out this web page: http://marinesurvey.com/yacht/corrosion_in_marinas.htmIf you are handy with a multi-meter you can check to see if you have current flowing from your AC grounding wire to your DC grounding system (or engine). Or you might determine (depending on direction of current flow) that other boats are grounding to water and the current is flowing thru your prop, shaft, engine and then across to your AC side to finally ground out to the marina ground.Good luck.A good solution for that is to install a galvanic isolator between your AC & DC grounding system (or it can be installed on the green AC ground wire). The isolator uses diodes to stop small currents (less than 1 volt or so) but still allows higher current to pass so that normal grounding occurs.

 

[Anthony Bavuso]

Nigel Calder's Book...

Nigel Calder's book "Boatowner's Mechancial and Electrical Manual" has a pretty extensive discussion of this problem which may help you determine the correct solution.I do not completety understand it all yet but from what I have read you can install a galvanic isolator or an isolation transformer into your AC shore power system.