Boats today have myriad power-hungry systems, such as air conditioning, stabilizers, refrigeration and other appliances. Typically, power is fed to those systems via shore power at the dock or from an internal combustion generator.

Generators are great at their job. They produce clean, reliable power and run for thousands of hours. A typical 7-kW generator will consume around half a gallon an hour of fuel under load. But that generator also makes noise, transfers vibration through the hull and emits exhaust. Also, generators are relatively large and heavy. They can create an installation challenge. Plus, locating an internal combustion engine within the mechanical spaces complicates the build with ignition-protection considerations.

There are alternatives. Inverters and battery banks have been providing power for refrigeration and other relatively low-power consumers for decades. However, they just haven’t been up to the challenge of massive loads such as air conditioning.

Today, advances in battery technology — particularly lithium-iron-phosphate (LiFePO4, or LFP) and more efficient, higher-output inverters — have been inching closer to enabling on-board comforts without an internal combustion generator.

Integrel Solutions

The first 48-volt product in the market came from Integrel Solutions, a company in the United Kingdom that spent 20 years bringing high energy production, engine-mounted alternators to market. Its first product, aimed at the sailboat market, can fit into relatively low-horsepower sailboat engines.

Integrel balances using excess horsepower from the engine with producing up to 9 kilowatts of power and storing it in LiFePO4 batteries. Up to 9 kilowatts of energy production from the main engine typically means the boat won’t need a generator. On space-constrained sailboats, this option frees up room for other equipment and systems.

The company is now working on systems capable of producing upward of 30 kilowatts of power by locating a power-generation unit between the engine and transmission. Potentially, the new system may be able to provide some propulsion, as well.

Fathom e-Power

Brunswick’s Navico Group debuted the Fathom e-Power system at CES in 2020. Brunswick launched e-Power on the Sea Ray SLX-R 400e. The system uses Mastervolt’s MLi lithium-iron-phosphate batteries along with inverters to provide power to the boat’s loads, including air conditioning, cooking appliances and a Seakeeper gyrostabilizer.

Initial boats equipped with Fathom e-Power utilized a 24-volt, 22-kW battery bank. According to Sea Ray, that is enough power to run the boat’s systems for eight hours. The batteries are charged by output from the engine’s alternators. In the case of the SLX-R 400e, that was three 450-hp Mercury Racing outboards. But the output of all three engine alternators isn’t enough to keep up with the load. So the system will slow the rate of discharge but won’t recharge it. For that, the boat needs to return to a dock and plug into shore power.

Arguably, e-Power’s biggest advance wasn’t assembling the components; that was done for quite a while before the system. The biggest advance was a control system that brought all the systems together and presented the boat owner with a simple, intuitive interface to manage it all.

Mercury Verado V-10 Dual-Voltage Alternator

Mercury’s Verado V-10 outboards have a dual-voltage, high-output alternator that can produce up to 7.2 kilowatts of energy at 48 volts. High-horsepower outboards are likely to be utilized in double, triple, quad and quintuple installations. Even with two dual-voltage alternators, there is more power available from the on-engine alternator than from the typical generator installation.

At first glance, that extra power may sound like a waste. But the newest iteration of Fathom e-Power, paired with Mercury’s new engine, allows more flexibility in how the boat is used. Charging is no longer limited to the end of the day when the boat has returned to the dock. Now, multiple-day trips and overnights away from shore power are possible. Plus, the intelligent control system means the boater doesn’t need to spend time managing power; the system will do it for them.

Paired together, Fathom e-Power and the Verado V-10’s dual-voltage alternator introduce a mode called Power+. Power+, the engine’s generator mode, burns a leaner fuel mixture for greater efficiency. The boater can select Extend or Boost mode. Extend runs the engine at a lower rpm and produces less power, while Boost runs the engine at higher rpm and maximizes power production.

Too Much Power?

It may sound like a boat with triple or quad Verado V-10s equipped with the
dual-voltage alternator is going to have too much power. The SLX 400 can be ordered with a traditional, 7.5-kW generator or the Fathom e-Power system. If it were fitted with three engines equipped with the dual-voltage alternator, it would have 15 kilowatts of output in Power+ Boost mode and up to 21 kilowatts of power production underway.

Generators are sized for the loads on the boat. Any time the air conditioning and other large loads are on, the generator will be running. Battery-driven systems are different. The batteries and inverter are sized for the loads, but, ideally, the charge sources will be as large as possible. That’s because the goal is to minimize the time required to charge the batteries and, hence, the time with the engines running. Minimizing engine run time, especially when the boat is at anchor, means being able to enjoy the natural surroundings. It also means greater efficiency.

The commercial 48-volt systems offered today all utilize LiFePO4 batteries. Their cycle life averages more than 10 times that of lead-acid batteries, so the installations should enjoy long lives before battery replacement becomes necessary. But perhaps more important than cycle life, LiFePO4 batteries accept a charge quickly. In fact, most of them can be fully charged in one or two hours. If the goal is minimizing engine run time, that’s a critical factor.

Why 48 Volts?

Most boats, especially those smaller than 50 feet, utilize a 12-volt electrical system. There’s no magic to 12 volts, but it’s what cars have used since the 1950s. Since many systems aboard boats are marinized versions of automotive products, it has made sense to stick with it. But the recreational marine and automotive industries have seen the demand on their electrical systems explode. With that increased demand comes stress on the existing systems.

Cable size is determined by the number of amps being carried by the cable, not by volts. Energy is measured in watts, which are volts times amps. So a 2,500-watt load at 12 volts is just over 208 amps. That same 2,500-watt load at 48 volts is just over 52 amps. The 208-amp load will require a minimum of 2/0 AWG wire, while the 52-amp load will require a minimum of 6 AWG wire. Per foot, 2/0 AWG wire weighs nearly four times what 6 AWG wire weighs. Depending on voltage-drop requirements, the difference in wire sizes may be even larger. In addition to the weight difference, larger wire is significantly more expensive.

The advantages of 48 volts aren’t limited just to wire size and cost. Typically, 48-volt components have a substantial efficiency advantage compared with 12-volt versions of the same component. For example, the dual-voltage alternator can produce 7.2 kilowatts in the same physical footprint as the 12-volt-only version produces 1.8 kilowatts. Inverters, chargers and other components also have greater efficiencies when paired with higher battery voltages.

48-Volt Power Gains Traction

For quite a while, many experts have understood the case for moving to 48-volt power systems, but have also understood the challenges. Nigel Calder, as part of his work on the American Boat & Yacht Council’s Electrical Standards Committee, has advocated for updating standards such as E-11 for 48-volt power. Calder pushed for changing the low-voltage threshold to 60 volts.

According to current ABYC and European regulations, 48-volt power is defined as low power and is covered by the same standards as 12-volt power. The threshold is currently defined as 60 volts. So even LiFePO4 systems that may see voltage in the upper 50s during charging are compliant.

The standards aren’t the only problem. For years, a move to 48-volt power has suffered a chicken-and-egg problem. Very few 48-volt systems were deployed because the availability of 48-volt consumers was limited. On the flip side, very few 48-volt consumers existed because of limited availability of the systems. Fortunately, we are now seeing significant momentum on both sides of the problem.

Today, a boatbuilder can buy 48-volt windlasses, thrusters, inverters, chargers, grills and more. There are still some items, including most navigation electronics, pumps and lights, that are only available in 12 or 24 volts. For these, DC-to-DC converters are necessary. But these relatively low-power devices aren’t problematic to power from a converter. Plus, with Mercury having introduced a dual-voltage alternator at the end of last year, it seems reasonable to expect that more 48-volt products will be introduced in response.

Challenges

Forty-eight-volt systems offer several advantages, but also come with some challenges. For early implementations, one of the biggest challenges has been the availability of components designed and certified for 48-volt use.

For example, LiFePO4 installations require a fuse with a high amp-interrupt capability. But none of those fuses were certified for use at 48 volts. So Brunswick’s Blue Sea Systems had to work with suppliers to certify fuses for this workload.

LiFePO4 batteries require more care to keep individual cells balanced within a battery bank. Dragonfly Energy, which makes Battle Born Batteries, has extensive experience with battery banks running at 48 volts. The company has found that over time, individual 12-volt batteries can drift out of balance. The fix is to break apart the bank and balance each 12-volt battery individually.

Based on the company’s experience, Dragonfly has announced a management system called Intelligence that includes a module to manage keeping the batteries in balance. It monitors the 12-volt batteries in the bank and alerts the user when they need balancing. The user can then initiate an automated routine that takes the bank offline, breaks it back down to 12 volts and balances the batteries.

The Future

It’s taken many years for 48-volt systems to gain traction, but the developments in just the past 12 months indicate that they’re here to stay. As with any technology, the more systems that are implemented, the further the technology will develop. Currently, the primary goal is an uninterrupted day on the water. As battery technology advances, it’s reasonable to expect that duration will increase. Advances in alternator technology will likely improve the rate at which batteries can be charged.

There’s also room for advances on the load side. Today, the vast majority of marine air conditioners run on 120- or 240-volt AC power. There are some 12- or 24-volt DC air conditioners, but extremely few that utilize 48 volts directly. Thus, 48-volt installations require conversion from AC to DC and the attendant conversion loss.

As the technology advances, boaters can look forward to enjoying their time on the water without the background noise of a generator. The need to start the engines should also decrease. And as management systems become more advanced, the power system won’t require the boater’s attention, allowing more time to enjoy the water and less time to manage power. 

This article was originally published in the May 2023 issue.