How to run boat at night when on water

Mark Searay

Member
Nov 10, 2019
114
Sydney Australia
Boat Info
Searay Sundancer 375
Engines
Mercruiser 6.5L x 2
Hi
As a newbie to boating , what’s the best way of running lights etc at night without destroying batteries?
Is it recommended to run generator at night instead of running off batteries ?
Any tips would be greatful
With thanks
 
I guess that will depend pretty heavily on what you consider "etc". :)

A properly maintained set of house batteries should have no problem running your lights, a fridge or two and the occasional sink/head visit for a night or two without running the generator. If you're having battery capacity issues in the AM with these kinds of overnight loads you likely need some new batteries...or perhaps there are other electrical issues that could use some attention.
 
Run the genny until right before bedtime to ensure batteries are fully-charged.
  • Convert the lights to LED
  • Minimize the time pumps run by:
    • doing washing etc. while genny is running in the evening
    • ensuring the the vacuflush system has no leaks (or shut it off at night)
    • ensuring the check valve in the sump is good so it doesn't cycle
  • Fill fridge and freezer with cold/frozen and dense items (beer cans and ice packs, frozen food etc)
  • Turn temp of fridge to a very cold setting while genny is running, then back up to a safe but higher temp off after shutdown
  • Avoid opening the fridge door until genny is running again in the morning
Start the genny again in the morning to re-charge batteries, heat water, run pumps, make coffee etc.

With healthy batteries and care, this routine can maintain 12V power indefinitely while running the genny 2-4 hours per day.
 
We never ran our genny unless we needed it for heating
IMG_4230.JPG
or cooling. The batteries were robust enough to handle lights, TV, and stereo for several hours. Our refrigerator had a cold plate so it didn't run much.
 
Hi
As a newbie to boating , what’s the best way of running lights etc at night without destroying batteries?
Is it recommended to run generator at night instead of running off batteries ?
Any tips would be greatful
With thanks

Like Stee6043 said a properly maintained 12 volt system should handle the demand with in reason. I can go out all day, run the Radio, Refrig, and whatever lighting needs to be used spend the night and be fine in the morning. And if you have too start the generator for a little while turn on the charger and put a little life back in the batteries !
 
Run the genny until right before bedtime to ensure batteries are fully-charged.
  • Convert the lights to LED
  • Minimize the time pumps run by:
    • doing washing etc. while genny is running in the evening
    • ensuring the the vacuflush system has no leaks (or shut it off at night)
    • ensuring the check valve in the sump is good so it doesn't cycle
  • Fill fridge and freezer with cold/frozen and dense items (beer cans and ice packs, frozen food etc)
  • Turn temp of fridge to a very cold setting while genny is running, then back up to a safe but higher temp off after shutdown
  • Avoid opening the fridge door until genny is running again in the morning
Start the genny again in the morning to re-charge batteries, heat water, run pumps, make coffee etc.

With healthy batteries and care, this routine can maintain 12V power indefinitely while running the genny 2-4 hours per day.

Rarely will you find more practical, useful advice on the internet than "fill the fridge with beer cans". This is forum gold, people. :):):)
 
Hi
As a newbie to boating , what’s the best way of running lights etc at night without destroying batteries?
Is it recommended to run generator at night instead of running off batteries ?
Any tips would be greatful
With thanks

On my 330 I have my house bank replaced with two 6v golf cart batteries in series. They are 232 Amp hour rated. I have all of my lights replaced with LEDs now and a new Nova Kool refrigerator, which reduces power consumption. The fridge uses 5.2 amps while running so assuming 25% running time (I doubt it runs that often) there is over 7 days of power to run the fridge alone. Lighting and stereo during the day reduce that capacity of course and I would never run it down to zero. LED anchor lighting maybe is 3 watts = .25amps (20 watts = 1.7 amps if you don't convert LED). So you will consume about 2 amp hrs overnight each night if you leave LED anchor lights on for 8 hrs (14 for regular bulbs). So anchor lighting is not consuming much.

I can easily be at anchor for a 3 day weekend without running the engines (I do not have a generator) and have enough to start the engine that shares the house bank at the end of the weekend (although it does turn over slowly).
 
I guess that will depend pretty heavily on what you consider "etc". :)

A properly maintained set of house batteries should have no problem running your lights, a fridge or two and the occasional sink/head visit for a night or two without running the generator. If you're having battery capacity issues in the AM with these kinds of overnight loads you likely need some new batteries...or perhaps there are other electrical issues that could use some attention.

Solid info!
When we sleep on the hook we just run the genny for cooking, AC, TV etc. until it’s time to go to bed.
Swapping all the bulbs in the cabin and cockpit courtesy lights to LED will cut down significantly on how much you draw and give you additional peace of mind.
 
Another newbie question in the topic:

When you are out and off shore power and you want to use your generator...
Do you leave everything in the position they are in for battery usage or do you switch it all back like you’re on the 110?

Thanks.
 
Another newbie question in the topic:

When you are out and off shore power and you want to use your generator...
Do you leave everything in the position they are in for battery usage or do you switch it all back like you’re on the 110?

Thanks.
I believe the most important thing is to know your boat and it's systems including it's capabilities and condition. Only with this can one determine the answer to these questions. For example, the generator on my boat pretty much runs from the time we disconnect from to the dock until we reconnect because of the AC and DC power the boat demands for us to fully enjoy it. I also know that the batteries in their current age/condition can carry the boat on anchor through the night easily without the generator running and not have to change the boat's power configurations. Every boat will have differing results consequently the need to know your boat...
 
On my 330 I have my house bank replaced with two 6v golf cart batteries in series. They are 232 Amp hour rated. I have all of my lights replaced with LEDs now and a new Nova Kool refrigerator, which reduces power consumption. The fridge uses 5.2 amps while running so assuming 25% running time (I doubt it runs that often) there is over 7 days of power to run the fridge alone. Lighting and stereo during the day reduce that capacity of course and I would never run it down to zero. LED anchor lighting maybe is 3 watts = .25amps (20 watts = 1.7 amps if you don't convert LED). So you will consume about 2 amp hrs overnight each night if you leave LED anchor lights on for 8 hrs (14 for regular bulbs). So anchor lighting is not consuming much.

I can easily be at anchor for a 3 day weekend without running the engines (I do not have a generator) and have enough to start the engine that shares the house bank at the end of the weekend (although it does turn over slowly).
Did you have to change your battery charger as well?
 
Another newbie question in the topic:

When you are out and off shore power and you want to use your generator...
Do you leave everything in the position they are in for battery usage or do you switch it all back like you’re on the 110?

Thanks.
I think you are asking if folks turn on different DC circuits when they turn on the generator? So they are not so much in battery conservation mode?

For my part I don't specifically energize specific DC circuits just because I'm on the generator. I use the genny to either charge the batteries or run specific AC-only equipment like the 3 air conditioner units, the ice maker, or the stove. The fridges and microwave work on AC/DC and an inverter, respectively. I generally turn on DC circuits or items when I want to use them and turn them off when I don't.

I guess the only thing I do specifically with the genny running is to turn on both AC legs of the panel. That lets me use the air con, the battery charger, and will auto switch the fridges from DC to AC power. I have to do that because I turn off the AC circuits when disconnecting the shore power.

Not related to your question, but I have some generator start up / shut down practices I follow. When starting I always let the generator come up to operating temperature before gradually turning on any AC loads - minimum 150 F. Then I turn on the AC load gradually. When stopping the generator I also always turn off the loads and allow the generator to cool down for a few minutes before shutting down. During these few minutes of no-load operation the operational temps will typically fall from 170 F to 150 F. It's better for the health of the generator.
 
Great thoughts in here, especially the "fill the fridge with beer" insight. When not at a marina, we seem to fall into similar habits to what's discussed here. Typically in the morning when we wake up, the genny goes on for making coffee, using the microwave or stovetop for breakfast, running the hot water heater for showers and cleaning up those breakfast dishes. During that, we have the batteries getting some juice. Most of the day genny is off, unless it's really humid and "she who must be obeyed" needs the A/C. In the evening, genny is usually back on to have hot water for rinsing off after swimming, making dinner, and cleaning up. Again, a couple hours that way at night and in the morning seems to do the trick for several days on the hook.

(Our endurance issue on the hook is usually fresh water, not electrical power, wish we had a bigger tank.)
 
Great thoughts in here, especially the "fill the fridge with beer" insight. When not at a marina, we seem to fall into similar habits to what's discussed here. Typically in the morning when we wake up, the genny goes on for making coffee, using the microwave or stovetop for breakfast, running the hot water heater for showers and cleaning up those breakfast dishes. During that, we have the batteries getting some juice. Most of the day genny is off, unless it's really humid and "she who must be obeyed" needs the A/C. In the evening, genny is usually back on to have hot water for rinsing off after swimming, making dinner, and cleaning up. Again, a couple hours that way at night and in the morning seems to do the trick for several days on the hook.

(Our endurance issue on the hook is usually fresh water, not electrical power, wish we had a bigger tank.)

If I am going for extended periods on the boat, I bring along some of those large square spring water jugs that I just refill with tap water from home. They fit in storage spots here and there and can be used for drinking, cooking, dishes etc. and help extend the 40gal tank. I also "shower" in the lake if we are not at a marina, which is a nice advantage of Great Lakes boating in our area.
 
Another newbie question in the topic:

When you are out and off shore power and you want to use your generator...
Do you leave everything in the position they are in for battery usage or do you switch it all back like you’re on the 110?

Thanks.

12 volt stuff stays where it is. My fridges and lights are easily handled by the batteries for full days or overnights on the hook.
The genny gets turned on mostly for showering, cooking and climate control in the cabin.
If the genny is running when the motors aren’t, I flip the breaker for the battery charger on.
My routine:
I shut off all the 110 breakers before unplugging from the dock.
If I decide to use the generator away from the dock the 110 breakers are in the off position before I start the generator. I let it run for a minute or so after starting, then I start switching 110 breakers on for the stuff I want to run.
When it comes time to turn the generator off I shut 110 breakers off, then shut generator off.
The 110 breakers stay switched off until I’m plugged in back at the dock.
 
Last edited:
These responses are REALLY helpful. This was just the kind of information I was looking for.
 
Another newbie question in the topic:

When you are out and off shore power and you want to use your generator...
Do you leave everything in the position they are in for battery usage or do you switch it all back like you’re on the 110?

Thanks.
Yes, when Gen is on, I continue using all 12v stuff. I do notice the main draw is the 2x bar fridges
I want to replace them with a more efficient fridge but unsure what the exact or best replacement is
II have a 2005 375 (340DA) Sundancer & believe the NovaKool are the best replacements.
 

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