An Expert Reflects

Nigel working at a test board evaluating electrical

Editor’s Note: With multiple marine book titles published (including his magnum opus Boatowner’s Mechanical and Electrical Manual), numerous articles in this magazine and others and the many seminars he’s taught at boat shows, marine systems expert and Ocean Navigator contributing editor Nigel Calder has built up an impressive body of work that has enlightened untold numbers of boatowners and continues to educate voyagers worldwide on the concepts and procedures involved in keeping a voyaging boat in good operational shape. Recently, Calder launched a web-based teaching effort called that allows voyagers to learn online at their pace. 

For his latest offering Calder will be teaching an in-person seminar on electrical systems this spring on April 17 and 18 in Portland, Maine. Ocean Navigator is a co-sponsor of the seminar along with Professional Boatbuilder magazine and Ocean Planet Energy. More on how to sign up below. 

As he was gearing up for this new seminar series we asked Calder a few questions about marine electrical systems and how things have changed and continue to change with designing, installing and operating a modern marine electrical system.

Ocean Navigator: What are the biggest changes you’ve seen in boat electrical systems since your book Boatowner’s Mechanical and Electrical Manual was first published in 1990?

Nigel Calder: Beginning in the late 1970’s, the progressive adoption of solid-state electronics into numerous components of boat electrical systems resulted in a qualitative shift in the capabilities of these systems. We saw the introduction of first-generation multi-step voltage regulators coupled to high output alternators, “switch mode” battery chargers, and “modified sine wave” DC-to-AC inverters. Taken together, and with constant improvements over the subsequent decades, these initiated a slow-moving transformation in onboard lifestyles to the point that nowadays it is just about possible to live the same energy intensive lifestyle on a boat as at home. 

The electrical side of the first edition of my Boatowners Mechanical and Electrical Manual described the necessary structure for these emerging systems and explored in detail the various components, starting with batteries. The knowledge for this was partly based on my own experience and experimentation, but primarily gained by picking the brains of the gurus of the day: Rick Proctor at Cruising Equipment Company, Bill Montgomery at Balmar, and, above all, Dave Smead at Ample Power Company. In the intervening decades, despite continuous increases in the power and complexity of boat electrical systems, the core energy creation and distribution structure has not fundamentally changed. The three subsequent editions of my Boatowner’s Mechanical and Electrical Manual have all retained the same structure as the original edition, but with a ton of additional material (the fourth edition is approximately three times as long as the first). 

A raft of new technologies is now beginning to have what I believe will be a similar transformational impact as the introduction of solid-state electronics in the 1970’s. In particular, on the energy creation and storage side we have lithium-ion batteries and on the distribution and load side digital switching systems. Pulling everything together are ever more powerful and integrated data processing and communication capabilities. Whereas the core knowledge and skillsets for designing, installing, and troubleshooting boat electrical systems have been incrementally expanded over the past several decades (to the point at which they can seem overwhelming to new boaters), this has been an evolutionary process. There are no fundamental technological changes. The new technologies are very different compared to the old. A whole new set of skills is required for systems design, installation, and troubleshooting.

Nigel using a hydraulic tool to make wiring for his Malo 46 Nada.

ON: Given the changes, do boatowners need a different mix of talents for working on their electrical systems?

NC: This does not mean existing knowledge is obsolete. At one level the electrical skillsets required of boatowners who want to work on, or troubleshoot, their electrical systems have not changed. Volts and amps are the same as they ever were. The same principles drive conductor sizing, overcurrent protection, and many core aspects of an electrical installation. These are embodied in the American Boat and Yacht Council’s (ABYC) E-11 standard (AC and DC Electrical Systems on Boats) and related standards. They are at the core of the online BoatHowTo Boat Electrics 101 course ( that I have helped to develop, and also at the core of the intensive one- and two-day electrical seminars that I have developed.

But at another level, the ever-increasing centrality of digital systems requires at least a basic understanding of onboard networks. This puts the boatowner solidly into the world of the National Marine Electronics Association (NMEA). 

For decades I have explicitly focused on electrical issues and left electronics to others! My interest and knowledge has stopped at the point at which the power cables connect to a “black box.” This degree of differentiation is becoming harder and harder to sustain — I am, as a result, currently discussing with the NMEA adding a Basic Marine Electronics Installer course to our BoatHowTo site, and we have added various network-related lessons to the Advanced Marine Electrics course at 

The good news for those who do not want to be dragged into the electronics world is modern electronics are extremely reliable so maybe this knowledge can continue to be left to others; the bad news is if the electronics go down, they can increasingly take down the entire boat electrical system. Knowledge of basic troubleshooting techniques and mechanisms to establish workarounds for failed networks are becoming ever more important skillsets.

On my own boat I have a first-generation Capi2 digital switching system (installed in 2008) which has been incredibly reliable. Unfortunately, the manufacturer went out of business in 2018, at which point any hope of technical support ended. I accumulated a stock of spare power distribution modules and a couple of touch screen control panels. I have the necessary software to program a new module or panel to the system and, I think, sufficient notes to help me through the process. I can likely track down component failures and am just about competent to switch out these components but will be in deep trouble if more extensive knowledge and diagnostic capabilities are required. 

When it was built, my boat was specifically wired for this system, which is not compatible with any of the digital switching systems currently available. Given a failure I cannot troubleshoot and correct, I will be looking at an extensive, time consuming, and expensive rewiring of the boat. 

Testing a large battery array.

ON: How do different battery chemistries affect your approach to designing and operating an electrical system?

NC: Lead-acid batteries have always been the weak link in our electrical systems and as such have driven much of the design process. Over the decades we have seen incremental improvements in performance, especially with Absorbed Glass Mat (AGM) batteries. This has been translated into higher performing electrical systems on our boats. Spearheaded by the Consortium for Battery Innovation (CBI), there is considerable ongoing AGM research into potentially significant improvements in energy density, sulfation resistance, and cycle life, all of which are important in marine energy systems. The research is mostly based around adding carbon in some form to AGM batteries. But until there is a major breakthrough, fundamentally we will still be using the same energy system design principles that emerged in the 1970’s. These principles are encapsulated in a concept known as the Mid-capacity Rule. 

Lithium-ion is a game-changer in almost all critical respects — energy density, weight, charge acceptance rates, voltage stability, usable capacity, immunity to sulfation, and cycle life. Lithium-ion batteries outperform lead-acid several times over. With lithium-ion, the Mid-capacity Rule is tossed out the window. The choke point in an optimized energy system has shifted from the batteries to the generating capability, and in particular to alternators. 

This led me a decade ago to focus on improving the generating side, culminating in the development of the Integrel system – a nominal 9 kW, 80 percent efficient alternator which ramps up its output at low RPMs. The combination of lithium-ion batteries and this, or some other variant of a high-powered, high efficiency, low RPM, alternator is, in turn, a game changer for those with moderately high energy needs. It removes the need for an onboard generator with considerably enhanced energy generation efficiency and much reduced fossil-fueled engine run time. Lithium-ion batteries are an essential component of these energy systems.

All such systems need to be engineered as a system, and it’s important to recognize that the new technologies come with their own issues. From time to time, you see lithium-ion batteries advertised as a “drop-in replacement” for lead-acid. From my perspective, this is nonsense. Lithium-ion has strict temperature limitations at both the high and low end (something I am finding out in a Maine winter with a newly purchased electric car). The theoretical high charge acceptance rates necessary for a powerful energy system are not available with many lithium-ion batteries currently on the market (it is important to read the small print). The batteries may trip out when faced with high instantaneous loads, such as from bow thrusters. There are numerous installation errors that can potentially result in thermal runaway and a battery fire, even with the so-called “intrinsically safe” lithium-ion iron phosphate (LFP) chemistry. 

If the battery management system (BMS) on any lithium-ion battery senses an approaching overcharge condition (or a variety of other fault conditions) it will disconnect the battery. Depending on the boat’s electrical system, this may shut the boat down at a highly inconvenient moment. It may result in damage to charging equipment. It can result in a voltage spike through the boat that blows out all operating electronic equipment (we have a recent example of $100k in wrecked electronics). Lead-acid batteries do not do this. Although an overcharge may damage a lead-acid battery, and wreck it if continued for an extended period of time, and in a worst case drive it into a lead-acid variant of thermal runaway, the battery will never suddenly disconnect, and in fact there is no mechanism for it to do this. 

For any lithium-ion installation where a sudden battery disconnect could be problematic, the BMS needs to be able to have some level of control over all relevant charging devices. This requires the BMS to have external communication. In the event the BMS senses an approaching overcharge condition, there needs to be a mechanism to warn the boat operator and shut down charging devices without damage to the charging devices (for example, in the case of an alternator, by turning off the field current as opposed to simply disconnecting the alternator).

These and other caveats which do not apply to lead-acid batteries should not be seen as a deterrent to using lithium-ion batteries. They are a warning that the batteries should be built by a company with a track record in the marine field and installed by a qualified person familiar with the emerging ABYC and ISO lithium-ion standards. 

I have a substantial bank of lithium-ion batteries on my own boat and love them. Coupled to an Integrel system, for the first time in decades we are not constantly obsessing about energy consumption and battery state of charge!

Nigel: “Sometimes finding space for all the gear can be a challenge.”

ON: Do wind, solar and waterpower systems raise special challenges compared to a system that charges only via a high output alternator or genset?

NC: From an energy management standpoint, yes. The energy sources are intermittent with the times and levels of energy availability not under boat operator control. Significantly greater levels of reserve capacity (i.e., batteries) combined with more active energy management are required as compared to an alternator or generator-based energy system.

From an installation perspective, fundamentally, no. There are the same conductor sizing, overcurrent protection, and other installation issues as with any energy source. In principle, you can feed as many different charging devices as you like to the same battery or battery bank. Assuming each energy source has an appropriate voltage regulator or controller, when a battery or battery bank approaches a state of full charge the charging device with the lowest full charge trip point will shut down first and the rest will follow sequentially based on their trip points. This presupposes all are wired correctly with minimal voltage drop.

There are, in particular, substantial benefits associated with solar power on any boat that has more than minor house loads. The cost of solar has come down steadily and the efficiency of higher quality panels has increased approximately 50 percent over the past decade or so. There have been important recent developments in solar controllers, notably ‘boost’ controllers which can take a panel with a nominal output below 12 volts and boost it to an optimized voltage for charging 12v, 24v, and even 48v batteries. 

ON: Any predictions for where electrical systems are headed?  

NC: This is hard to say. Politically, the pressure to eliminate fossil fuel consumption is growing. I believe it will become increasingly unacceptable to burn fossil fuels for pleasure. 

The energy needs of numerous boating applications can already be met from lithium-ion batteries and shoreside charging. But from a practical standpoint, this is simply not possible with any conventional boat that requires significant propulsion range. With the exception of foiling boats, we are limited by the physics of wave resistance drag, and the manner in which it, and the resulting propulsion power requirements, increase as cruising speeds are approached. The energy density of the best of today’s lithium-ion batteries is as little as one fortieth that of an equivalent volume or weight of diesel fuel. For a couple of decades, lithium-ion energy density has been increasing, but we are beginning to approach the theoretical limits and the curve is flattening. We are not going to get to where we need to be with incremental improvements in existing technologies. And there is no way improvements in solar, or maybe fuel cells, are likely to fill this gap fast enough to keep up with demands for electrification. 

However, there are a couple of possibilities that may not come to fruition, but which illustrate that these, or some other yet to be discovered technology, will provide the necessary solution. The first is some variant of a metal/air battery, a number of which have theoretical energy densities many times higher than lithium-ion, and the second are carbon neutral fuels that extend the life of existing fossil-fueled engines in a carbon neutral manner. These fuels, based on carbon capture combined with hydrogen derived from electrolysis of water, are needed by the airline industry and as such are seeing a high level of investment. 

ON: What was your worst electrical system problem?

NC: We’ve had few significant electrical problems on our own boat at least in part because I have typically followed my own advice and wired things properly and conservatively! However, I’ve destroyed three windlass motors because of a habit of gunkholing, running aground, and using the windlass to kedge off. 

The incident that really stands out harks back to hybrid and electric propulsion experiments in 2010.

We had a 30 kW electric propulsion motor powered by a large bank of AGM batteries, with supplementary power from a DC generator. We were exiting Kungsviken fiord in Sweden at night via a relatively narrow, rock-strewn passage with the generator running to reduce the rate at which the electric motor was discharging the battery bank. The rectifier block for the generator caught fire in dramatic fashion, with the flames standing out against the blackness of the night. I looked at the blaze and thought “I could sell this photo several times over” but lost my nerve and instead of grabbing my camera grabbed a fire blanket and smothered the fire. Wish I’d had the nerve to take the picture!

But now we were down to rapidly diminishing battery power and limited electric propulsion range with a significant tide pushing us seaward and limited anchoring options on the margins of the channel. Adrenaline ran high as we maneuvered in the dark to find a spot with swinging room in which to wait for the tide to turn. We limped back to Kungsviken in the morning to regroup. n

Sign up for Nigel’s electrical seminar on April 17 and 18 by going to For more info: