[bell2132]

I need some HELP!!!!
I was out anchored this weekend running the fridge and stereo for about two hours (which we normally do). When we went to start up the engines the starboard engine cranked right up but when we went to start the port the entire boat died (stereo fridge everything was dead). After about 5 minutes everything came back online and I turned on the generator. After running the generator for about 10-15 mins I tried starting up the starboard engine and everything died- the generator shut off, along with the stereo and fridge again (I repeated this step but trying the port engine- same result) In a final attempt before calling a friend to pick us up I ran the generator for a while then shut off all the breaker switches for everything on the boat except for the engines ignitions etc. I was able to get the starboard engine running but when i went to turn the key on the port engine the bell rang for a millisecond before the whole boat died again (didn't even get to the point where i could try to turn the engine over). Again I tried these same steps with starting the port engine first with the same result.
We left the boat out there over night and went back in the AM to try to get her started- same thing. I went below suspecting a bad battery and tested both the house and engine batteries all individually (I disconnected all the connecting wires), they all had 13.2 volts each. After further testing I held in the battery parallel switch below the ignitions and was able to get the engines running however the second i released the switch both engines and the whole boat died. I went behind the helm and disconnected the parallel wires from the switch and spliced them together. We were able to make it home (where I reconnected them back to the switch). After being plugged into shore power the engines crank right up (even after disconnected shore power and trying to recreate the same scenario) ANY IDEAS? I don't want to take the boat out knowing we could have this issue again and we have a trip planned for this coming weekend with a group of friends!!!

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Also, one more thing to add. The next morning during the process someone used the head, we turned on the vacu-flush and everything was fine but when we went to put on the water pump the whole boat died again.

[TIARA44]

How many batt's on each bank?  What type?  How old are they?  When you were running the Gen, did you have the battery chargers on?  Have you checked the output of the Alt's on the engines?

[jclark003]

Without a wiring diagram that may be difficult to diagnose. Seems to me If your entire 12v electrical system is dropping offline (house and start banks) I would start by looking at the groundIng wires coming off the batteries. If the problem were on your +12v side it would show up only on that one bank (house or start) so I would be looking at the common wires that are shared across both banks (ground).

More than likely all your batt grounds are strapped together and then go to a bus bar, engines, etc. A bad connection or wire can create a lot of resistance and sometimes act like a switch when batt voltage drops (say after starting an engine) or when the connection gets hot. And that will definitely affect both 12v systems/circuits.
You may want to put your volt meter on a good +12V source then move the black lead across the battery grounds and then the bus bar. Do the test wih the batt charger off and look for a voltage drop at one of the terminals. a resistance test across each ground wire may also help as will an IR thermometer after pulling a good load (again with batt charger off)

Some others on the forum may be able to offer better advice. Good luck.

[bell2132]

Thank you all for your help. We consulted many marine electricians and all were puzzled and unable to recreate the issue. We replaced all three house batteries and all three battery switches below the cabin steps- this seems to have solved the issue thus far, hopefully we don't run into this again.