Electrification has been an increasingly common buzzword in the marine industry, especially in the past four to five years. Most notably, the recreational marine industry is seeing advancements in lithium-ion batteries, electric propulsion and the need for charging infrastructure.
We can attribute the electrification revolution — both in on-board power supply and electric propulsion systems — in large part to developments in battery technology. Although batteries have improved since the first lead-acid battery was constructed in 1859, this type of battery technology still has shortcomings. Lithium-ion batteries addressed many of those problems; these batteries tend to be more suitable for larger loads and to deliver more usable energy. They also have a much longer life span and provide much higher energy density.
The vast majority of lithium-ion systems installed on boats use lithium-iron-phosphate (LiFePO4 or LFP) batteries. LFP as a cathode material has very high thermal stability, which means these batteries are much safer than cobalt-based, lithium-ion batteries.
Using quality batteries and cells is important. The market is flooded with lithium-ion cells of unknown quality, and many boat owners might be tempted to opt for those low-priced products. Even the best system can fail if subpar batteries are used.
Nevertheless, correct installation and system design are important for the safety and performance of the boat’s electrical system. The American Boat & Yacht Council responded to industry demands for guidance when installing these batteries, first with a Technical Information Report (TE-13) that will be superseded this year by an updated Standard E-13, titled Lithium-Ion Batteries. While Standard E-13 does not contain any testing requirements, it refers to industry-accepted IEC and UL testing standards that battery or cell manufacturers need to follow.
Regardless of chemistry, one of the most important terms when discussing lithium-ion batteries is safe operating envelope, a set of operational parameters that the battery manufacturer specifies. These parameters include high- and low-voltage limits, charging and discharging current limits, charging and discharging temperature limits, and so forth.
To ensure that the battery operates within these limits, each battery (or battery bank) should have a battery management system (BMS). A BMS is an electronic circuit designed to protect a lithium-ion battery from hazardous situations such as overcharging or overdischarging, or charging or discharging in high and low temperatures. If the BMS senses that any of these conditions exist, it will disconnect the battery from the charging sources or loads.
The primary objective, as ABYC and the associated technical committees established with Standard E-13, was to ensure safe installation and operation of the battery system without placing constraints on developing technology. Therefore, even though the majority of boat lithium-ion batteries are lithium-iron-phosphate batteries, the document does not limit installers to one cathode chemistry.
Peukert’s law, presented by the German scientist Wilhelm Peukert in 1897, approximates the change in capacity of rechargeable batteries at different rates of discharge. As the rate of discharge increases, the battery’s available capacity decreases. Compared to lead-acid batteries, lithium-ion batteries are affected by Peukert’s law to a much smaller degree. They can handle high discharge currents without losing too much of their usable energy.
This quality is exceptionally handy when we start thinking about electric propulsion. Electric motors used for propulsion are high-current loads, so Peukert’s law and low energy density are limiting factors for traditional lead-acid batteries in propulsion scenarios. The development of energy-dense lithium-ion batteries that can be deeply discharged by high currents without losing their capacity lifted the barriers that electric boats experienced in the past.
Because of this, electric propulsion is no longer limited to low-speed craft with trolling motors. Today, we see large yachts and high-speed boats utilizing electric motors.
Some electric propulsion systems operate at very high voltages, so proper installation is essential. In 2018, ABYC developed Standard E-30, Electric Propulsion Systems, that addresses the design, construction and installation of alternating-current (more than 300 VAC, but less than 1,000 VAC) and direct-current (more than 60 VDC, but less than 1,000 VDC) electrical systems on boats for the purpose of propulsion.
High-voltage systems have unique safety requirements. As an example, the standard requires an emergency stop that disables the propulsion system, an insulation fault monitor, battery voltage and temperature monitoring, an isolated electrical system, disconnectors that simultaneously open the positive and negative side, and more.
Most major boatbuiders and propulsion manufacturers are researching and developing new electric products. There are several technical aspects where we can expect to see new developments. Charging is one example.
The combined charging system (CCS) is an open, universal standard solution for quickly charging large battery banks like those in automobiles and, more recently, electric boats. Unfortunately, only a handful of marinas have rapid-charging stations. Installing these fast chargers requires upgrading the marina’s electrical systems.
Most boats have access to a shore power receptacle, which can be used for recharging batteries using the boat’s on-board chargers, but just not as fast as a CSS can do it. In the end, some boat owners might decide to go off the grid and generate power with solar panels, fuel cells or traditional generators. This is a dynamic and emerging segment of the boat market, and we will see new products in the near future.
Shore Power Demands
This electric revolution is not limited to propulsion systems and batteries. Boat electrical systems are getting more sophisticated with customers’ growing demand for more electrical power.
Large inverters are becoming a norm, not only on big yachts but also on smaller cruising boats. For example, many boat owners want to be able to use air conditioning without running a noisy generator, or their boat does not have adequate space for one. Large lithium-ion battery banks combined with inverters and high-output alternators that can quickly recharge the batteries are the solutions we see more often, on boats and RVs.
ABYC Standard A-31, Battery Chargers and Inverters, addresses design, construction and installation of battery chargers, power inverters and inverter/chargers. The standard covers such topics as installation, grounding requirements and labeling, and everything else a marine technician needs to know to ensure safe installation and operation of this part of the electrical system.
Higher demand for robust on-board electrical power leads to more sophisticated AC shore power systems. Particularly on larger boats or commercial vessels, we likely will see more AC shore power converters, which will typically provide electrical isolation, frequency conversion and voltage conversion between the shore outlet and the boat’s electrical system. Additional capabilities may be included as required by specific installations (such as phase conversion, power conditioning and/or synchronization). ABYC Standard A-32, AC Power Conversion Equipment and Systems, addresses the design, construction and installation of electrical and electronic power conversion, control equipment and systems.
It’s easy to see the level of complexity and new technologies used in boat electrical systems. ABYC’s role is to provide technical information for the marine industry by developing safety standards that allow for safe implementation of all these new technologies. We are fortunate to have a group of industry professionals who volunteer their time working in project technical committees and subcommittees to help develop technical standards that ensure we are always able to address recent trends. n
Maciej Rynkiewicz is standards developer at the American Boat & Yacht Council.
This article was originally published in the October 2022 issue.