For most boat owners an onboard generator is a necessary evil. Yes it’s great to be able to power a host of electrical accessories and appliances when away from shorepower, but a genset can annoy with noise and vibration. Plus, its internal combustion engine requires maintenance and exhausts potentially dangerous carbon monoxide. House battery banks and inverters are alternatives to a genset, but the energy supply offered by heavy AGM (absorbent glass mat) lead acid deep-cycle batteries is limited and not practical on a boat equipped with power-hungry systems such as air conditioning and a gyroscopic stabilizer.
But we are living at the dawn of the age of lithium. The energy to power our boating adventures may well soon be stored in lithium iron phosphate (LiFePO4) batteries, rather than in a gallon of gasoline or diesel fuel. We may be a long way from an all-electric powertrain that can match the value, performance and range of an internal combustion engine, but soon production boat buyers may encounter a LiFePO4 replacement for that genset.
Lithium batteries that provide 120-volt power are not uncommon on large power and long-range sailing yachts; they’re often paired with a genset for charging when shore power is not available. Companies such as Battle Born Batteries and Victron Energy offer LiFePO4 batteries and the required control systems for the DIY boat or RV owner. But in January 2020 Advanced Systems Group (ASG) by Brunswick Marine used the Consumer Electronics Show in Las Vegas to reveal Fathom e-Power, a system combining a high-capacity lithium-ion battery pack with an intuitive power management system that’s intended to replace a genset. The technology leap is that Fathom is designed as an integral part of the boat, functioning as invisibly as the power system in an electric car.
“Most of the Fathom components are off the shelf from ASG brands Mastervolt and CZone,” says Dr. John Reid, Brunswick Corporation vice president of enterprise technologies. “We created the engineering architecture required to make it work as an integrated and safe system. All of the components communicate with each other on a common BUS network to make sure the load side, battery storage and charging sides of the system are in sync and actively managing the power system. The boat owner can be confident that the boat is watching over the system and taking action, or notifying the user of different states of operation.”
Today Fathom e-Power is available as an industry-first option to replace the standard Westerbeke 7.5-kW generator on the Sea Ray SLX 400 Outboard day cruiser with a bank of four Mastervolt LiFePO4 batteries scaled to power accessory systems for about eight hours before recharging by shore power or through the alternators of Mercury Verado outboards. The Fathom e-Power option adds $24,385 to the boat’s retail price, which starts at around $720,000. The 2022 Sea Ray SLX 400 Outboard, well-equipped and with Fathom, is around $1 million.
The foundation of Fathom is a bank of four 5500-watt/400-amp-hour Mastervolt MLI Ultra 12/5500 LiFePO4 batteries (about $6,000 per battery), each with a proprietary battery management system (BMS) that communicates battery state of charge through CZone to the Simrad MFD at the helm. Each battery weighs about 125 pounds, according to Troy Kollman, director of advanced engineering at Brunswick Boat Group, who adds that the four batteries occupy roughly the same footprint as the standard genset. These batteries are about 70 percent lighter than lead acid batteries of the same capacity and have a life span of up to 3,500 charge cycles, seven times the life of lead acid batteries.
Typically about 80 percent “depth of discharge,” or DOD, of the stored energy of a LiFePO4 battery is usable (about 20kWh of the total 22kWh capacity of this battery bank). AGM lead acid batteries have a 30 to 50 percent useful DOD, and the life of the battery is quickly diminished if drained below that point, which frequently happens when an AGM battery bank is used with an inverter for 120-volt power.
A pair of Mastervolt 6-kW CombiMaster inverter/chargers manages charging and switching when the boat is connected to shore power. Charge time with 120-volt shorepower is about five hours if all boat systems are inactive. A Mastervolt Chargemaster 12/25 provides a dedicated charging source for AGM lead acid engine starting batteries. A Mastervolt Charge Mate Pro smart battery combiner isolates the LiFePO4 battery bank from the starting batteries, and optimizes the charge rate from starting batteries to the LiFePO4 batteries. When triple Mercury Verado 300 or Mercury Racing 450 outboards are running, each 115-amp alternator charges to the starting batteries, and power is siphoned from those batteries to the LiFePO4 batteries, so the alternators are never directly charging the lithium batteries. Charge time from 20 percent with the outboards alone is about 10 hours, so engine charging is really meant to restore the state of charge to a useful level if the LiFePO4 batteries are drawn down.
This sounds quite complex, and it is, but it has been engineered for “frictionless” boating. Cool down with the AC, fire up the electric grill and the water heater, hoist the anchor with the windlass. The power is there, and you didn’t have to flick a switch. The user-interface, which is integrated into the Simrad MFD at the helm, shows percent of battery life remaining, time to empty, and time to recharge based on current power consumption and charging levels.
Kollman expects other boat builders will attempt to create and offer a similar battery system. “As we continue to develop Fathom, we’ll begin to scale it for different boats, and even different markets,” says Kollman. “For example, a boat headed to the Bahamas might require more battery capacity to run constant air conditioning than one destined for a cooler climate like Michigan. Fishing boats will have different demands than a day cruiser like the Sea Ray. In fact, I think one of the most-appealing applications will be for boats that currently can’t offer a genset because there’s not enough room belowdecks. We could engineer Fathom to fit in that space.”
Could it be time to say goodbye, genset? The future could be lithium-powered.
This article was originally published in the November 2021 issue.