Does My Boat Need a Generator in 2024?

Conventional thinking is that a liveaboard cruising boat should have a generator. Sure, plenty of people make do without one, and many arguments exist against getting one. 

But a few key modern technologies are making them increasingly less important. Let’s examine marine generators from the cruising boater’s perspective. 

What Is a Marine Generator Really For?

First off, what exactly does a generator do on a boat? Generators make electricity, specifically 120/240-volt AC, for use with big appliances. You generally can’t run these things off of batteries; items like air conditioners, heaters, water heaters, and (in some cases) watermakers use too many watts and deplete the batteries too quickly. 

The generator also charges the boat’s house battery bank when running. This is actually one of its most important jobs. Standard lead-acid batteries, whether flooded cell, gel, or AGM style, do not function well if allowed to drain below 50 percent repeatedly. The less often you drain them, the longer they’ll last. Deep-cycle lead-acid batteries are better, but they have the same operating stipulation. You can buy cheap batteries, keep your boat plugged in at the dock, and run the engine and/or generator all the time when you’re off the dock, and your batteries will last many, many, many years. 

The battery charging function of a generator is very important. Many boaters do not have their boats set up for overnighting away from the dock, so running the generator is the only way to keep the batteries from draining and reducing their lifespan. This ensures you have plenty of power for anything you want to plug in without worrying about conserving electricity.

Alternatively, boaters who are used to living on the hook will have deep-cycle batteries with enough capacity to run the things they need to. An inverter can provide 120/240-volt AC power from the battery banks. A good battery monitor works like a fuel gauge for your batteries and tells you when to turn on the engine for charging. Some boats operate this way, even with a generator, simply to save fuel and keep the boat quiet. The purr of a generator, even an inboard one in a sound enclosure, can get tiring after a few days. 

New Technologies Changing the Requirements

This formula for generator use changes every day. The single biggest factor changing things for boaters is new battery technologies, namely lithium-iron phosphate (LiFePO4 or LFP) marine batteries. 

Modern lithium batteries have many advantages over their old-school lead-acid counterparts. The biggest advantage, however, is their ability to be drained well below 50 percent (in some cases as low as 10 percent) without harming their longevity. Good lithium batteries are rated for 3,500 cycles or more while drained at a 90 percent depth of discharge. 

There’s some confusion about the safety of these batteries simply because they use lithium in their chemistry. There are many formulas of lithium batteries used in different devices and vehicles. Some are more volatile than others. The LiFePO4 batteries used in boats are some of the safest and most forgiving. However, they still require professional installation with a host of safety systems (BMS-Battery Monitoring System) to ensure that batteries are never overcharged or abused. 

With lithium batteries, there’s no reason you would need to run a generator while swinging on the hook overnight. The batteries can be run down and then charged the next day when you get underway.   

Boaters with lithium systems can also draw huge amounts of power from their battery banks. On large cruising boats, it’s not uncommon to find two or three-kilowatt inverters—comparable to a small standalone generator. With enough capacity in the house battery bank, these systems can easily run any appliance you desire, including air conditioning. 

Lithium batteries still need to be charged, of course. Solar energy is only good until the sun stops shining, and wind energy is only good if the wind blows hard. This means these boats will still need to run their engines, use a standalone generator, or plug into shore power to top up the batteries sometimes. But with enough solar panels and careful conservation of their power, many boaters can avoid these things unless absolutely necessary. 

Advantages of a Built-In Marine Generator

Marine generators are great tools to have aboard, even if you don’t always use them.

• Easy, push-button starting when needed and the option for auto-starting in cases of low voltage.
• Provides nearly unlimited power anytime, including running air conditioning overnight. 
• They are nearly silent thanks to a sound enclosure, vibration-free mounts, and water-muffled exhaust. 
• Ties into the boat’s fuel and electrical systems to integrate everything for easy operation. 
• They help your boat’s resale potential. Most liveaboard cruising boaters are looking for vessels equipped with generators and air conditioning. A boat with these items will command top dollar and sell faster than other options. These two systems are very expensive to install later, so buyers are likely to put them on their “must-have” list. 
• Quieter, easier to use, and safer than portable generators
• More efficient, quieter, and less expensive to run than the engine/alternator for battery charging.

Disadvantages of a Boat Generator

There are plenty of reasons not to have a generator on your boat.

• If your boat didn’t come with one, putting one in is prohibitively expensive. The unit is costly, and labor and installation costs will likely double the total cost. $$$
• Like all engines, they need to be used regularly and maintained. Maintenance costs are the same as having another inboard motor—fuel filters, oil changes, coolant, etc. $$$
• A generator will take up space in your boat, reducing your storage space for other items. If you’re putting one in, you’ll likely notice the loss more than if you never had that compartment available for storage from the outset. 

Making Do With a Portable Generator

Cruise long enough, and you’ll eventually meet someone who uses a portable gasoline generator instead of a built-in unit. A 2,000-watt portable can be had for between $500 and $1,000. Why would anyone spend $15,000 or more for a built-in marine unit? 

There’s no right or wrong answer. Anyone who tells you it’s wrong or unsafe to use a gas generator on a boat isn’t looking at the reality—lots and lots of folks are doing it. But you need to know the risks, and you need to mitigate those risks. 

The portable generator is a hassle to use. It must be stored somewhere and carried onto the deck when you want to use it. Extension cords must be run and starter cords pulled. 

Once it’s running, it is noisier than any built-in generator. You might be happy with the noise, sitting in your cabin running the air conditioning, but the folks on the boat next to you won’t be so impressed. Like a campground, using a portable generator means you’ll need to impose your own “quiet hours” when you shouldn’t run it within earshot of any other boats. Sundowner time is definitely quiet time. 

Over the past seasons, we’ve noticed more people continually running their portable generators while at anchor. To us, this is unbelievable—running one of those vibration-making noise machines on your boat is not pleasant, and certainly not why we’re out here boating. 

That said, we own and use a portable Honda generator. It doesn’t see much use because we have our boat set up for off-the-grid living and do most of our charging from solar, wind, and the occasional motoring trip. When it does get used, it’s for a few hours at a time at most.

So, who’s a portable generator right for? If you’re a boater who wants continuous air conditioning and hot water on-demand, you should get a built-in marine generator. A portable is likely sufficient if you’re more like us and just need to run the generator occasionally to top the batteries after a cloudy week or to run a watermaker. It will still be, however, a pain in the ass.  

Safety with Portable Gas Generators

As mentioned above, using a portable gas generator is not without risks. The primary concerns arise from the carbon monoxide in the exhaust fumes. Since the exhaust system is not plumbed, you must ensure the exhaust stays away from the cabin area and is safely blown downwind. The swim step might not be the best place—on some boats, the air flows forward toward the cabin. Conditions might change as the wind changes, so keeping the generator downwind of the living quarters can be tricky.

At a minimum, you should have a carbon monoxide detector on board. You should have one even if you don’t have a gas generator, but the generator makes it really important. 

Gasoline onboard can also be dangerous, as gas vapors can build up, causing an explosion. Many of us have gas outboards for our dinghy, but the generator is more likely to be stored in a sealed compartment on the big boat.

Finally, you must realize that a portable generator will not be connected to the boat’s ground safety wiring system. Furthermore, they operate with a floating neutral, which may cause your reverse polarity lights to illuminate. 

Do your research and only take risks you understand and are comfortable operating with. While many people operate portable generators onboard, it’s never an ideal solution. 

Does Your Boat Need a Generator?

So, do you need a generator on your boat? Every boater makes their own decisions, but here’s how it’s worked for us.

We’ve made do without a built-in genny for eight years, spending most of that time away from docks and without air conditioning. (We have AC but only use it when plugged in at a dock, which is rare.) We do have a portable Honda that we bring out only when absolutely necessary. But here are a few things we have to make this setup work:

• High-end, deep-cycle AGM (last boat) and lithium batteries (new boat).
• Sufficient solar power to keep the batteries topped up. 
• A good battery monitor (Victron) that helps us monitor the battery depth of discharge and meter our energy use.
• High-output 170A Balmar alternator to help top-up the batteries when we motor, usually every few days. 

Even still, we still occasionally wish we had a built-in generator. It would remove the hassle of having the portable and keeping gas onboard for it (we’ve moved to an electric outboard on the dinghy), and we would use it more often during the winter months when solar output isn’t high enough. It would also be super nice to have air conditioning, enabling more nights away from the dock during the hot summer months. There’s no sense in adding such a complex system to our current boat, so for now, we just sail to Maine each summer.