Marine electric and hybrid propulsion consultant Jamie Marley discusses the rise of electric propulsion across the boating world today – a world where power versus weight and delicate performance tolerances rule …

Walk around any boat show today and you will see a broad selection of propulsion solutions – from outboards to sterndrives, surface drives to jet drives. As in the case of sail, the world of powerboating, it would appear, has tried almost everything to successfully cut a course through the waves. And in terms of the energy required to drive these various propulsion options, the marine industry continues to push the bounds, not only in refining the internal combustion engine but also in exploring the potential benefits of HVO and even hydrogen. (Yanmar and Yamaha are two such companies that see hydrogen as representing an exciting and worthwhile alternative to fossil fuel for a whole array of commercial and leisure applications.)

Likewise, the shift towards electric propulsion is not just a trend but a significant move towards a more sustainable and efficient maritime environment. However, the relevance of the latter, in particular, depends greatly on its application, as well as the design and hydrodynamic quality of the craft in question.

As in the case of the other technologies, the development of electric propulsion is being driven by environmental concerns, technological advancements and a desire for cleaner, quieter and more efficient watercraft. With such a fast-developing technology ‘fuelling’ this ever-expanding industry, it’s more than a full-time job keeping abreast of this technology and the associated choice of electric boats on offer. So in this article, we will seek to highlight the current issues at stake and the relevance of electric power, as well as those uses and situations where e-technology can be best applied.

Service issues

Due to the speed at which this innovation in technology is becoming available, service, support and expertise are all under pressure – yes, under pressure to develop at an appropriate and commensurate rate. Furthermore, if we are to be honest, the skills gap is only getting bigger, and this isn’t just a UK problem but a global e-power issue.

With larger propulsion systems operating at 400V and above, specialist technicians are in short supply to aid with installation and commissioning, and to provide a high-quality level of service cover.

There is a distinctive difference between low- and high-voltage propulsion systems too. Usually, the low-voltage (<50VDC) systems are worked on by experienced marine electricians who will likely have received the manufacturer’s training.

But what we lack today is a choice of local solutions where owners and operators can find a service centre that provides adequate support, specialised knowledge and an attractive turnkey approach to customer service. To combat this, some manufacturers are investing in training local marine companies and dealerships with the aim of giving proper support to customer projects on a national and international level. In this respect, it’s reassuring to see the drive toward the building of training centres, along with the necessary resources required to educate the workforce of tomorrow. (Courses that include elements related to electric and hybrid propulsion systems can be found at Bournemouth & Poole College, Lloyd’s Maritime Academy, the University of Southampton and South Essex College.)

The Avator 110e

ePropulsion X20

Making claims

Recent concerns about the safety of battery technology have drawn into focus the fact that electric boat insurers have some unique challenges set before them. This is thanks largely to the new nature of this technology and its specific risks – risks that relate to electrical safety, fire, water ingress and charging procedures, among others. After all, electric boats are still relatively new, which means there is limited historical data available for insurers to assess risks accurately. This lack of historical data can make it challenging for insurers to determine appropriate premiums and coverage levels.

Electric propulsion systems and battery technology tend to be more expensive than traditional marine propulsion systems. Take, for example, the Frauscher Mirage, which is available with either a standard petrol engine or an electric drive. The latter option, however, represents a 13% increase in price. As a result, the cost of repairing or replacing electric components in the case of damage or loss can be greater, leading to potentially higher insurance premiums. But marine insurers appear to have been quick to assess the risks, and underwriters also seem content that any e-power risks can be adequately managed. The wider industry is also beginning to make advances in the form of regulative measures, along with the establishing of common standards.

Insurance companies such as Pantaenius, Noble Marine and Navigators & General are all examples of insurers who now specifically give e-power as an option within their online application fuel type selection.

Evoy Storm 300hp electric outboard fitted to an Axopar

Evoy Storm 300hp electric outboard

Out of range

Range, understandably, represents the number one question for those considering the electric option. Of course, this doesn’t relate to motor technology so much, but rather battery technology – something that’s developing in its capabilities all the time.

And when talking about range and performance, the weight of the craft and its hydrodynamics become central to the whole issue too. Moving a boat through water requires far more energy than that which a road vehicle needs. The dynamics are totally different, and in a sense, a boat is far less efficient than its road-going counterpart – if for no other reason than the fact that water is more than 700 times denser than air! All of this means that boatbuilders need to build holistically and not adopt the viewpoint that simply bolting an electric motor onto a conventional hull is going to provide a working solution, because invariably it doesn’t.

The manner in which a planing boat operates can be likened to driving an EV up a hill – continuously! New electric boats and propulsion system technology are still widely challenged by the hydrodynamics that affect a boat’s range. But when analysed, what the likes of Tyde have achieved with their ICON craft, for example, allows us to better appreciate what can be done to reduce the negative effects that water density has on the energy required to move an object at speed. However, while adding more battery capacity – in theory at least – adds to the distance that can be travelled, there is that inevitable tipping point where power and weight take an all-decisive stand against each other. In this instance, there will only ever be one winner.

Four strokes are the only option for offshore.

By and large, in times past, we have not had to be overly concerned about hull efficiency. If more performance were required, one simply increased the horsepower, with the difference in fuel burn being negligible as a result. Unless ultimate high performance was being sought, weight and hydrodynamics have often been quietly viewed as less of a priority. But electric boating is different. One simply doesn’t have the luxury of those same tolerances or options as found in the world of 4-stroke and diesel engine power. Therefore, the entire make-up of a craft has to be considered if e-power is to work effectively.

Electric boats are much more restricted in terms of range than conventional ICE (internal combustion engine) boats. This is due to the present energy densities of today’s batteries (circa 150Wh/kg @ pack level, 2023), and also the limitations of the charging infrastructure as it stands at present. Energy density is the key to enabling a boat to reach its destination – without sinking it with sheer battery weight. For example, an Evoy 126kWh battery pack weighs in at 800kg.  

Fossil fuel outboards are the long-range power choice.

Energy densities of 200Wh/kg (pack level) are already used in EVs today, so we are likely to see this being implemented in marine applications within the next two years. Battery manufacturing industry statistics and predictions show, however, that by 2030, we could be seeing energy densities increasing to as much as 500Wh/kg (@ cell level). That’s big!

In plain terms, it has been predicted that the battery technology of tomorrow could be four times the energy density we see today. It follows that, in theory at least, electric boats could therefore be achieving four times more distance on a single charge than they do today.

The all-important cost

With rising fuel prices, the thought of running your boat on a lower-cost fuel such as electricity is enticing. But will it pay dividends? The truth for most of us boaters is that the cost is something we would like to bury! Let’s face it, the total cost of ownership (TCO) is a rare selling point used in boat sales. But could electric boating be different?

In the main, boats simply aren’t used or owned for long enough. So for an electric boat owner to recoup enough savings from such benefits as reduced maintenance, improved reliability and lower fuel (electricity) cost, the boat has got to be used for considerably more than 50 hours per year.

This raises the question: does the next generation of boaters even want to own a boat? After all, there’s a reason why e-boat rental companies and boat clubs are already big business across the world. These facilities play right into the hands of new boaters who want that instant boating fix without the usual strings attached.

GOT Marine Powered By Evoy Twin Breeze 120OB

In safe hands

Consider the unthinkable: a thermal event on board a boat. Surely this represents our worst nightmare, regardless of whether it involves electric or conventional fuel. So, are electric boats safe or safer than conventional craft? You could argue that they have fewer moving parts and that they already employ proven technology –

one example being lithium-ion batteries, which have now been around for decades. But even so, it would be fair to say that we view e/power as being an innovative technology in terms of maritime and boating in general, even though marine lithium-ion battery technology is drawn from some of the most established battery cell manufacturers in the world.

Manufacturers now understand lithium battery technology better than ever. But what must come now is an undertaking on the part of the industry with regard to standardising procedures, protocols and precautions when designing, installing, operating and then disposing of lithium batteries.

We are also now seeing the first ‘solid-state’ batteries being coupled to electric boat propulsion systems. Unlike conventional lithium-ion batteries, which use a combustible liquid electrolyte to transport ions between the electrodes, solid-state batteries use a non-flammable solid material as their electrolyte. The solid electrolyte allows for the faster transfer of electrons, which enables a safer and faster charge time. This technology is also more tolerant of high voltages and temperatures.

EPTechnologies are one of the first propulsion system manufacturers to offer solid-state batteries. The inherent qualities of SS batteries have led to them having their safety benefits dramatically demonstrated at trade fairs of late, with a nail being driven clean through the cell without any ill effect.

In conclusion, the electric boat industry is undoubtedly making significant strides. While challenges persist, the industry’s commitment to innovation, efficiency and sustainability is steering it towards a promising future – one where electric boating is no longer niche thanks to lower, more realistic entry costs.

The journey has just begun and the horizon looks promising. As we motor into the future, as an industry professional, I would say that the e-power tide is turning, its time is coming. But in the meantime, select with care and ensure that your expectations are aligned with your application/intended use. Remember the old adage ‘Horses for courses’. If you get the combination right, you could be onto a winner and electric power could be your answer to a form of boating unlike any other. May the force be with you!

Hull enhancements

Hull coatings such as Hempel’s Silic One can play a very big part in reducing friction on the surface of a hull. This can make a difference of several knots and not only provide better top-end speed but also improved range.

Foiling solutions from the likes of Sea Air Solutions and foiling kits such as those produced by HydroFin are all developed with a view to bettering hull performance and introducing more aerated lift, as well as reducing drag. Be cautious, though, as the world of foiling is very complex, and getting a foil working correctly in relation to not only the hull but also the engine set-up is a science in itself. Companies renowned for their efficient hull designs and specialist application work include Petestep AB and Pascal Technologies AS.

Chargers

Cruising with an electric boat is, and will always be, different. But EV-style marinised DC fast chargers, such as those installed at strategic locations along the coast by the likes of Aqua SuperPower, will, in time, enable electric craft to be seen as viable coastal cruising craft. The embryonic start of such a charging network can already be seen in the Solent region here in the UK. Aqua SuperPower have deployed EV-style DC charging solutions at Ocean Village (Southampton), Hamble Point, Cowes and Trafalgar Wharf (Portsmouth). (An additional five locations along the south coast of England are already in the planning stage too. Likewise, limited sections of the south coast of France and stretches of the Italian coast are gradually increasing their provision.)

E-hire & boat clubs

Rental boat companies, whose fleets require reliability, lower operating costs and green credentials, look set to benefit heavily from e-technology, which has flexibility and sustainability at its core. Electric boats typically require a higher initial investment, which, for many people, means they can be cost-prohibitive. The battery alone is a high percentage of the total cost. But the cost of lithium batteries will undoubtedly continue to lower. Pack prices in 2024 are approximately £75 per kWh, with the expectation of hitting £50 per kWh by 2030 (source: BloombergNEF).

Where the marine industry is challenged is the availability of marinised batteries. These often take some time to become available, lagging behind the latest and greatest, as seen in other applications, such as in the EV market. But for those of us interested in a simpler solution, electric boat rental companies include Classic Boats of Venice and, nearer to home, GoBoat, who have five Thames (London)-based centres. Then there are the boat clubs, of course, such as the aptly named The Boat Club, who offer a fully electric Lasai GL 20 for rental in Poole Harbour.

Charging benefits

It’s worth remembering that if your electric boat is kept at your home, it could continue to benefit you as an energy storage device to help buffer your domestic demands. Aqua SuperPower are already in the process of testing this technology in the UK.

The power maths

Quick maths: kWh divided by motor kW times top speed = nm of range at max speed. An example of this can be seen in Evoy’s Goldfish X9 RIB. Fitted with a 126kWh/300kW Hurricane inboard e-motor, it has a range of 25.2nm at a top speed of 60 knots. X Shore’s Eelex 8000, meanwhile, has a 126kWh battery installed. The boat’s 170kW drive affords it a range of 22nm at a maximum speed of 30 knots. Finally, Optima’s E10, which uses 126kWh batteries and a 40kW RAD drive, has a maximum speed of 15 knots and a range of 47.5nm.

For further reading on green boating take a look at our Sustainable Boating articles, including ‘Is electric boating green?’ and ‘The price of power’