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electrical systems at startup

i need to lean on the collective wisdom of this group with a question: what needs to be shut off (shore power/ house power) when starting the diesel? the previous owner of galileo is no longer around but left specific instructions regarding start up: disconnect the shore power, shut off all internal a/c circuits before staring. the talk on the dock from other owners of a variety of sailboats is as varied as there are boats in rock hall.
any suggestions? galileo is a 1984 384 with mostly original electrical system. it would be reassuring to know i am doing this right.


Mark Pearson
Staff member
I’ve never heard of any special requirements either. We probably are connected to shore power 50% of the time when we start. We haven’t fried anything that we know of. Some people are super religious about throwing the breaker on shore power before connecting/disconnecting. We are not super religious about that either and we haven’t fried anything in 30+ years on dozens of different boats.;)


The only reason I can imagine to do this would be to protect your batteries from some sort of hypothetical overcharging situation. The AC and DC systems are separate. Shore and alternator charging shouldn’t have anything to do with each other.

I’d be willing to bet the practice stems from suspicion of 110-12v converter/chargers. If your charger is less than 20-30 years old you’re probably fine because they all have fancy battery management software, but I can see being paranoid that the combination of shore power and alternator power could pump too much charge to the battery bank. It seems reasonable to worry that the two charging methods wouldn’t play nicely together. Or if you were perhaps using some ancient battery charger that had both feeds running through a single unit? If I had that, I would probably make a habit of unplugging first too...

On our boat, the shore power converter/shore charging is entirely separate from my alternator charging circuit (which I think is the norm, and I believe it is how these boats were originally wired). It should be perfectly safe to start the engine with shore power plugged in.


James M. Cleary
As others have mentioned, there should not be a need to disconnect the shore power connection when starting the engine. The previous owner may simply been an over cautious person. What concerns me in your original post is the phrase "mostly original electrical system". When the Morgans came out of the factory they had nearly dangerous electrical systems. Both 12V and 110V systems were so unsafe even for the codes of the 70's and early 80's. By todays standards, including the ABYC standards, both systems if still in their original configurations, are an accident waiting to happen. As a new owner of an older boat, I would dig deeply into bringing both systems up to current code standards.

In all the years I have been posting on this board, I have been very pessimistic about the Morgan's electrical systems. I was a construction electrican in NYC for 37 years, working under the NYC electrical codes and the National Electrical Code. The first thing I did when we purchased Dana in 1987 was to rip out the entire 110V system. It was that bad. Please give serious thought to overhauling the electrical systems.



Terence Thatcher
Hey Jim, on the subject of the AC system: A couple of years ago I installed a new water heater that runs off the engine or AC. (And yes, I had an electrician redo my AC system before I did that.) Anyway, the manual said I should install a 3 prong plug for the heater so I can unplug when gone from the boat for extended periods. Why switching off the panel breaker switch isn't enough I don't understand. Do you? Anyway, being obedient, I did that--and I hate it. I worry the plug will get knocked part way out somehow under the sink and cause problems. Is there a complete breaker switch I could install instead, something that is hard wired with all three wires but would be like pulling the plug when I leave the boat? Does any of this make sense to you? Thanks.


James M. Cleary
By switching off the circuit breaker you are breaking the connection to the 110V positive leg. If the system is done to ABYC standards, the circuit breaker will also break the 110V negative (neutral) leg. It will not break the ground leg (the U shaped prong). That could cause an issue with the unit if there is a problem with the grounding system on the boat. It could allow the flow of electrons through the ground to the water heaters internal parts and possibly to the sea. This is electrolysis. In building construction a similar precaution is sometimes taken with garbage disposal units in sinks. A wall plug is installed under the sink to break the total connection when the system is being serviced. I think your water heater company is covering all their bases by being over cautious. But it's not a bad idea. You can ease your mind by coating the 3 prongs with a bit of a non-electrical conductive grease, then tape the connection closed to prevent an accidental parting of the plug. There are also commercially sold plastic housings that will keep the plug together. I don't know of a circuit breaker that will break the ground leg along with the hot & neutral. What I have a question about is, what is considered an extended period of time for leaving the boat? Overnight, a week, winter hauling???