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Old 08-15-2021, 09:43 PM   #1
City: Nevada City
Join Date: Aug 2021
Posts: 7
Newbie to a Grand Banks 42 Classic

Hi all,

I just purchased a GB42, 1995 from a private party. He went over the systems and operation of the boat but even after that I have a few questions that he wasn't able to answer:

1. When he demonstrated the departure procedure, once shorepower was disconnected, he started the Onan and switched from short to generator. Then he started the main engines for departure. I asked him why the generator was necessary while underway and he couldn't explain. My thinking is that the alternators will keep the batteries charged. Am I wrong to think running the generator while underway is senseless?

2. When on shorepower, are the AC outlets powered directly by the shorepower or still off the inverter? In other words does the shorepower go solely to the battery charger?

Many guess is I'll get some great answers.
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Old 08-15-2021, 10:06 PM   #2
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Welcome aboard. Congrats on your new boat. Running the generator while underway isn’t usually necessary. Not unless you are running something like A/C that draws a lot of power. As to how the outlets are powered it depends on how the boat is wired. Get a certified marine electrician to look it over and explain it to you.
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Old 08-15-2021, 10:08 PM   #3
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I had a little snort when I read the previous owner's response. Does the generator have similar hours to the mains?

Starting the generator before getting underway is SOP for some, but not for most with boats like yours. Climate control needs the generator running. Maybe that's why it was always on.

Most inverters will pass through shore power when available and go to DC source when not available. But it's hard to make generalizations, especially on a 25 year old boat. Never make assumptions!
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Old 08-15-2021, 10:47 PM   #4
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Congrats on your GB 42 - a beautiful and satisfying boat in so many ways. As noted above in posts #2 and #3, the generator is unnecessary for operating the boat - just for certain systems, like HVAC or cooking. As to the AC outlets, likewise what the others said - better get a marine electrical pro to clarify how your particular system was set up.
"Less judgment than wit is more sail than ballast. Yet it must be confessed that wit give an edge to sense, and recommends it extremely." ~ William Penn
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Old 08-15-2021, 11:32 PM   #5
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Are you handy with a DVM? Where's your boat berthed?
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Old 08-16-2021, 12:04 AM   #6
City: Clearwater
Vessel Name: Seas the Bay
Vessel Model: 1981 Hardin 42 Europa/Sedan
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I can't speak for your boat, but let me offer this...

I was taught to run my genset anytime I'm underway, and I do. Aside from liking air conditioning in the cabins, it ensures that the genset exhaust is under positive pressure anytime I am running.

This makes it nearly impossible for following seas or rapidly backing down on throttle to force water into the exhaust and cost me the genset's engine.

It isn't universal, but most genset installations don't have enough height in their exhaust to give a big margin of safety. Running the genset boosts that margin of safety by a metric boat load.

And, I write the above as someone who spent about a grand soon after buying my boat to relocate the genset muffler and rerun the exhaust just to get a few more inches of height. I take a belt and suspenders approach. What's the cost? A little more diesel? The genset will last longer running than rotting, I think, so I'm not concerned about hours.

To the person who asked about hours, my genset has more than my mains. It gets started before I disconnect shore power, well before I depart. It gets shut down after reconnecting shore power and cooling off a bit, well after I arrive, and it runs every time they shut off dock power for a major storm or it otherwise "just goes out" for too long.

As for which outlets are on an inverter...disconnect from shore power and give them a try. You can use a meter, a radio, a light, whatever.

The inverter may be full-time, such that the charger or alternator or solar or wind supply the batteries and the batteries supply the inverter and the inverter /always/ supplies the power to those outlets. But, they more commonly incorporate a transfer switch, so they only supply the power if the shore power isnt there.

If you want to test, after finding out which outlets are on the inverter, reconnect to shore power and turn the battery switch(es) supplying the inverter off. Then see if the outlets work. If they do, it demonstrates that the inverter isnt inverting on shore power.

But, please don't ever turn a battery switch with an engine running, unless you are triple sure it is safe. It is mostly commonly a problem when switching between batteries. Most switches are break-before-make, meaning if you switch from Battery-A to Battery-B there is an interval of no connection. During that time the alternator suffers a current surge that likes to eat diodes, etc. Basically, once loaded, you want to keep a load on an alternator or the regulation can go crazy when the load abruptly drops off.

Happy boating!
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Old 08-16-2021, 12:34 AM   #7
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City: Vallejo, California
Vessel Name: Mahalo Moi
Vessel Model: 1986 Grand Banks 42 Classic
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Originally Posted by FlyWright View Post
Are you handy with a DVM? Where's your boat berthed?
Yes! Tell us where your boat is berthed.
"Mahalo Moi"
1986 GB-42 Classic
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Old 08-16-2021, 01:00 AM   #8
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Does it have stabilizers? That might be a reason to run genset. Otherwise, unless using mains powered devices from the get go, I wouldn`t run it. That the seller couldn`t explain it suggests a learned habit rather than a known need.

It`s very likely the shorepower and the genset feed the same outlets, but check and see.
2005 Integrity 386 "Sojourn"
Sydney Australia
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