Inverter or generator?

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Docktopus

Member
Joined
Mar 23, 2024
Messages
15
Vessel Name
Docktopus
Vessel Make
Rodman 900
Hi all, I think this is probably a stupid question, but I would appreciate some help. Our boat is fairly new to us, and much more complicated than our previous boats. We have not had an inverter before. The basic question is when do you use your inverter or your generator? I basically use the inverter when there are other boats around so I don’t disturb them. The rest of the time I use the generator for all AC / 110v needs.

My particular setup is limited, two 4d batteries and I think only one of those is a house battery. We are preparing for a couple week long cruises over the summer, our previous experience is one or two nights at anchor or at a dock with power. Thanks in advance for your help!
 
I use my inverter as much as possible. I run the generator to power the air con or to heat water and of course to charge the batteries. With only a 4D house battery you don't have much reserve to power the inverter so it sounds like you will have no choice but to run the inverter. You didn't describe what kinds of AC loads you have but it seems like you may be want to consider some upgrades if you plan to spend much time on anchor. Solar could help.

 
Hi all, I think this is probably a stupid question, but I would appreciate some help. Our boat is fairly new to us, and much more complicated than our previous boats. We have not had an inverter before. The basic question is when do you use your inverter or your generator? I basically use the inverter when there are other boats around so I don’t disturb them. The rest of the time I use the generator for all AC / 110v needs.

My particular setup is limited, two 4d batteries and I think only one of those is a house battery. We are preparing for a couple week long cruises over the summer, our previous experience is one or two nights at anchor or at a dock with power. Thanks in advance for your help!
I use the inverter always, and use the generator only to charge the batteries when they get low. But that might depend on your inverter capacity.
 
Congrats on your new boat! What did you get and where are you located (proud papa pics too.....)?

Part of the reason I ask beyond curiosity is it can make a difference in recommendation and advice. Would also be helpful to know size of the inverter and if it's wired to run the entire boat or just key components (though some heavy loads are usually not run through the inverter). Would also be helpful to have an idea of your intended cruise - how big is your family, where are you headed. Will you be anchoring or staying in marinas or both? Will you move every day (giving your batteries a chance to recharge) or sit at anchor for a day or two?

Your OP has two components. When to use an inverter, and battery capacity which will play a big role in how much you can use your inverter. For capacity, you have to consider the 12vdc loads too, not just the 120vac because they all share the same reservoir of energy - the 4D battery. Assuming a healthy battery, you don't want to discharge more than about 50% - which is 12.2v for a lead acid battery. You have around 75AH to work with (half the 150AH rating of a healthy 4D). Not a lot, but workable. It's surprising how much power it takes to run/charge small electronics such as tablets and phones. An old-school incandescent anchor light will consume up to 10-12 AHs overnight - 15% of your overall capacity.

At anchor, you can probably run the microwave or electric coffee maker for short periods off your setup. I say "probably" because with high amperage draws off a small battery bank, the voltage of the battery 'sags' and may trip a low voltage alarm in your inverter. With engine running, the alternator is providing enough power into the battery to offset the power being drawn from appliance. Or you may find that what worked fun in the day when battery voltage was high won't work well in the morning after 12-hours of voltage decline.

Many people develop a rhythm of generator running. A couple hours in the morning to charge the batteries, heat water for showers, and cook if they have electric range vs propane. They also run the the generator for an hour or two in the evening, perhaps coinciding with running air conditioning.

BTW - depending on your alternator setup (twin engine vs single, large output alternator), will probably take at least a couple hours of engine run time to fully recharge a 50% discharged battery.

Hope this helps. Probably more info than you need.....

Peter
 
I would defiantly consider enlarging your house bank. But a lot goes back to Mvweebles points.

You must do the math, total loads, time using those loads = total amps needed TO the size of you house bank.
 
Hi all, I think this is probably a stupid question, but I would appreciate some help. Our boat is fairly new to us, and much more complicated than our previous boats. We have not had an inverter before. The basic question is when do you use your inverter or your generator? I basically use the inverter when there are other boats around so I don’t disturb them. The rest of the time I use the generator for all AC / 110v needs.

My particular setup is limited, two 4d batteries and I think only one of those is a house battery. We are preparing for a couple week long cruises over the summer, our previous experience is one or two nights at anchor or at a dock with power. Thanks in advance for your help!

You'll find it useful to pin down things like that "I think only one of those is a house battery" issue. Your overall capacity will instruct (and maybe also restrict) your inverter usage.

We use our genset underway when we need AC (aircon). Inverter, otherwise, and that services our 110V household fridge and freezer plus whatever 110V appliances we might want for short periods (microwave, etc.).

At anchor, we use the inverter as much as possible -- we prefer quiet -- and especially overnight. Daytimes, we run the genset to recharge batteries and power our water heater... timed to coincide with cooking times (electric galley).

Our genset is quiet enough so we don't have to worry much about "disturbing" other boats around... We don't run it overnight but that's more because we don't want to disturb ourselves.

-Chris
 
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I set my boat up with a large second alternator to facilitate powering the inverter while underway. As the refrigerator is 120 VAC the inverter is on all the time, either inverting or as a battery charger.

Inverters give you the ability to run modest to moderate loads without starting the generator. What they also allow you to do is significant loads while underway, provided you have a large output alternator. As an example, I did laundry with my Splendide washer dryer while underway.

With the exception of occasionally recharging batteries while anchored for a few days, 90% of my generator time was climate control. For an 8 month cruising season, I would normally average 100 hours of generator time per year.

Ted
 
Thanks everyone, this is all helpful.
 
Congrats on your new boat! What did you get and where are you located (proud papa pics too.....)?

Part of the reason I ask beyond curiosity is it can make a difference in recommendation and advice. Would also be helpful to know size of the inverter and if it's wired to run the entire boat or just key components (though some heavy loads are usually not run through the inverter). Would also be helpful to have an idea of your intended cruise - how big is your family, where are you headed. Will you be anchoring or staying in marinas or both? Will you move every day (giving your batteries a chance to recharge) or sit at anchor for a day or two?

Your OP has two components. When to use an inverter, and battery capacity which will play a big role in how much you can use your inverter. For capacity, you have to consider the 12vdc loads too, not just the 120vac because they all share the same reservoir of energy - the 4D battery. Assuming a healthy battery, you don't want to discharge more than about 50% - which is 12.2v for a lead acid battery. You have around 75AH to work with (half the 150AH rating of a healthy 4D). Not a lot, but workable. It's surprising how much power it takes to run/charge small electronics such as tablets and phones. An old-school incandescent anchor light will consume up to 10-12 AHs overnight - 15% of your overall capacity.

At anchor, you can probably run the microwave or electric coffee maker for short periods off your setup. I say "probably" because with high amperage draws off a small battery bank, the voltage of the battery 'sags' and may trip a low voltage alarm in your inverter. With engine running, the alternator is providing enough power into the battery to offset the power being drawn from appliance. Or you may find that what worked fun in the day when battery voltage was high won't work well in the morning after 12-hours of voltage decline.

Many people develop a rhythm of generator running. A couple hours in the morning to charge the batteries, heat water for showers, and cook if they have electric range vs propane. They also run the the generator for an hour or two in the evening, perhaps coinciding with running air conditioning.

BTW - depending on your alternator setup (twin engine vs single, large output alternator), will probably take at least a couple hours of engine run time to fully recharge a 50% discharged battery.

Hope this helps. Probably more info than you need.....

Peter
Thanks, Weebles. There will be four of us onboard for 10 days. Plans aren’t firm yet, if the conditions are suitable we will head to Monterey for a few days diving and will spend more time on a dock. If the conditions don’t favor taking a 30’ boat out of the gate we will be cruising the delta and trying to spend more time at anchor. I really appreciate the explanation on looking at amp hours and trying to calculate exactly our use. I’ll be working on that before the trip, scheduled for late July. We have a few long weekends planned before then to get a better understanding.
 
#doctopus

I would argue that no conditions would favor taking most 30 foot boats out the gate for what is a significant distance to Monterey. What is the make and model of your boat?

Also the diving in the area is usually close to shore so not likely you can anchor and dive off your boat. Even if you could sitting in a boat in the nearly constant swells waiting for the divers to surface would be challenging to most. I did that on a near perfect day in Monterey on a 58 foot boat and it still pushed me pretty close to the rail!

I would suggest you enjoy the delta and explore around the SF Bay for awhile. The NorCal coast is challenging and while you can make the trip in a 30 footer it could be hazardous and likely not a fun trip for all. Especially given this boat is new to you I would really caution not to go to Monterey.

So much to do and see without getting out the Gate.

I spent 20 years in the area including Monterey, Santa Cruz, Half Moon Bay, SF Bay and Delta. I am headed up to SF and Delta from San Diego in a week. I have 40 years of boating experience but would not go out beyond the gate in most 30 foot boats and even then not unless there was a really compelling reason. Sure there are days where it is glass but in a 30 footer even 4-5 foot seas would be extremely unpleasant (if not unsafe) for 50+ miles. I am going in a 48 ft very heavy full displacement boat and it still is not a walk in the park.

In the Delta you will have near zero risk of anything bad happening and overall a much better experience. You can drive the car to Monterey and stop at the Santa Cruz Boardwalk on the way home!



 
#doctopus

I would argue that no conditions would favor taking most 30 foot boats out the gate for what is a significant distance to Monterey. What is the make and model of your boat?

Also the diving in the area is usually close to shore so not likely you can anchor and dive off your boat. Even if you could sitting in a boat in the nearly constant swells waiting for the divers to surface would be challenging to most. I did that on a near perfect day in Monterey on a 58 foot boat and it still pushed me pretty close to the rail!

I would suggest you enjoy the delta and explore around the SF Bay for awhile. The NorCal coast is challenging and while you can make the trip in a 30 footer it could be hazardous and likely not a fun trip for all. Especially given this boat is new to you I would really caution not to go to Monterey.

So much to do and see without getting out the Gate.

I spent 20 years in the area including Monterey, Santa Cruz, Half Moon Bay, SF Bay and Delta. I am headed up to SF and Delta from San Diego in a week. I have 40 years of boating experience but would not go out beyond the gate in most 30 foot boats and even then not unless there was a really compelling reason. Sure there are days where it is glass but in a 30 footer even 4-5 foot seas would be extremely unpleasant (if not unsafe) for 50+ miles. I am going in a 48 ft very heavy full displacement boat and it still is not a walk in the park.

In the Delta you will have near zero risk of anything bad happening and overall a much better experience. You can drive the car to Monterey and stop at the Santa Cruz Boardwalk on the way home!



The boat is a Rodman 30, sold in Europe (where they are much more common) as a Rodman 900. It is a semi-displacement hull with twins. I am surprised by your response. Let me tell you a bit more about us and let me know if you still think the same way.

We bought the boat in Santa Cruz in December and kept it down there for four months. We were able to spend about 10 days cruising in Monterey Bay. We also brought the boat up from Santa Cruz and she handled the trip very well. We were in a good weather window, with 5-6’ swells and a 10-12’ period.

Our previous boating experience is a little over 10 years cruising the bay and delta. The boat was a very straightforward Bayliner 24’. I am struggling a little bit figuring out the more complicated systems on this boat, hence my confusion on when exactly I should use the inverter and generator. That’s also how I ended up on the Trawler Forum - needing to understand all the equipment I now have.

Our favorite Monterey dive boat - Beach Hopper II is a 30’ boat. I don’t know the hull design, but it is roughly the size and weight of Docktopus. We probably splurge on boat dive once or twice a year, so we have had plenty of time experiencing the swells during surface intervals. Admittedly, MaryJo is a professional and a much better captain than I am.
 
Thanks, the background does help. To answer if it changes my position, if you are only planning a week or so I would still favor staying inside the gate if only to avoid having to make the return when the weather might be snotty. Sounds like the main objective in Monterey is diving so just speaking for me I would go on the dive boat and save the fuel, time and wear and tear for some other adventure.

Reading your first post I was envisioning a 30 foot run about with a new owner perhaps lacking ocean experience. Seems you are comfortable with your experience and confident in the boat so if you feel comfortable and it is worth the effort of course you should follow your plan.

I agree the weather you experienced was indeed good but getting that for a week or more might not happen and sometimes a forecast is just wrong. Since it is based upon averages there will be bigger swells and waves than forecast. Your boat looks like a nice one and way more suitable than some other 30 footers. But for me I would still have a lot less stress and fun in the SF Bay and Delta. :)

If you do decide to go to the Bay/Delta I will be up there around the 3rd week of June and leaving our boat for perhaps a year in the Delta then hopefully proceeding north to the PNW.

To provide some perspective to east coast boaters who might be following this thread, here is the forecast for Monterey Bay and nearshore waters for this week. There are better conditions and worse conditions of course but due to the coastline, water and land temps, currents, bottom slopes and a big fetch all the way from Asia it demands respect.

NW wind 25 to 30 kt. Seas 13 to 16 ft. Wave Detail: NW 14 ft at 10 seconds.

FRI
NW wind 20 to 25 kt. Seas 11 to 15 ft.

FRI NIGHT
NW wind around 25 kt. Seas 11 to 15 ft.

SAT
NW wind 20 to 25 kt. Seas 11 to 15 ft.

SAT NIGHT
NW wind 20 to 25 kt. Seas 9 to 13 ft.
 
SF Bay and surroundings are my home waters. I only went to Monterey a few times but loved the place. Marina is right in town - my wife and I had a magical time there.

You won't need air conditioning along the way in that area (would be nice in the Delta but probably not necessary for your boat with open cabin area). So the biggest energy consumer will be refrigeration. I'll take a stab at consumption at around 50AH per day because that's what the small fridge in my camper van used. Given you'll be moving the boat each day or plugged into a dock, I think you'll be okay with just running the generator when cooking (looks like most of these boats have electric, but perhaps yours is different). You probably have a voltmeter on the electrical panel - my suggestion is to make sure you understand it, specially that it measures your house battery and there is no possibility of depleting the start battery. Also need to make sure the battery that starts generator is isolated - would be an issue if you need the generator to charge the battery but can't start the generator due to depleted battery. I have very robust meters on my new Blue Sea panel but I still recommend installing a Victron SmartShunt. They're under $150 and fairly easy to install. They give excellent SoC (State of Charge) information so you don't have to mentally do the math that 12.1v = 50% for example. While I think anyone appreciates increased battery capacity, your boat is usable as-is with careful monitoring. That said, if the battery is old, could really cause you some nuisance grief along the way.

As far as running SF to Monterey, your boat should be able to make the run in 6-7 hours assuming it carries enough fuel for the 100 nm run. That would allow you to leave at first light and arrive before the afternoon winds kick up. The bigger challenge is returning to SF with weather on the nose. Sounds like you work a regular job so it could be difficult to coordinate your vacation schedule with weather. Sounds like the Delta is your Plan B which is great. We lived in downtown San Francisco and loved the Delta for it's laid-back atmosphere (sort of redneck in a good way). The dry heat was a welcome change from San Francisco's cool summer temps. I still cherish my copy of Hal Schell's book on cruising the Delta. So much local history and color.

At any rate, your question was on inverter vs generator. If you have electric cooking, I'd plan on running the generator for meals. Battery charging will happen when generator is running so not much to worry about. If you have propane cooking, you'll need to monitor electical consumption via voltage readings and run the generator as needed. Fully charged with engine alternator running should see around 13.4v. With engine off, will drop quickly to around 12.5v. Attached is a Volt vs SoC table you might find helpful. Somewhere around 12.2-12.3 volts is probably the trigger for you to start planning on recharge, either by running your engine or the generator. I'd probably want to top up the batteries before bedtime so they aren't super low in the morning with the fridge running and night.

Good luck - BTW, love the name "Doctopus."

Peter


Screenshot_20240529_044416_DuckDuckGo.jpg
 
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Thank you so much Peter and Ken. I have learned A LOT from these interactions. I know I don’t have a trawler, but I am so grateful for your willingness to pass along your knowledge. Since I have propane cooking, it turns out that I probably don’t even need an inverter unless I want to plug something in. Even the microwave is 12volts (Do these things even work?). The only 110v I have is two air conditioners, the water heater, and a few outlets.

I also have a relationship with a professional captain that we used for some training. We have confirmed that if we have the boat in Monterey and the weather turns ugly, he will bring her up in the next good weather window.

Thanks again for your generosity in sharing your expertise with me!
 
Also thanks to Ted and Chris, all of the information I’ve gotten out of this thread has been valuable. It started out as a stupid question, but I have learned a lot. I also really appreciated Chris’s comment that I need to get from “I think only one of those is a house battery” to “I know only one of those is a house battery.” The design of the boat is pretty clearly to have one battery for the house and one for the engines, but it is twenty years old and there are lots of gremlins hanging out in our electal system.

Thanks again to everyone! The generosity on this site is amazing!
 
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