Is it time to switch to an all-electric boat?

Increasing numbers of new vessels of all descriptions are all-electric, with systems including propulsion, induction hobs and electric ovens, hot water and dinghy outboards.

But can all this really work in practice? And how realistic is this type of technology for the average cruising boat owner?

There’s certainly no shortage of cynics online and on social media who will tell you all-electric will never work.

Yet demand for boats with these systems is continuing to grow and an increasing number are successfully sailing across oceans or proving to be comfortable nomadic floating homes.

However, it is the other end of the spectrum – day-sailers and weekenders – that were first to adapt to electric propulsion in a big way.

It’s already close to a decade since the market arguably reached maturity, with more than 50% of new models in these categories launched at the Düsseldorf boat show designed from the outset primarily for electric motors, even if internal combustion engines remained available as an option in some cases.

So which view is correct? And do any of the naysayers have a point?

As is often the case, the answer is “it depends”.

An all-electric boat can be a perfect match for some owners, while others might be better served by a hybrid solution.

A number would still be better off with a conventional internal combustion engine and more traditional cooking appliances.

But even ostensibly similar boats can be used in very different ways, hence a solution that works for one owner may be unsuitable for another.

A recent report by ICOMIA, the International Council of Marine Industry Associations, found that on average recreational craft clock up only 35-48 engine hours per year.

This means for an average user the report found that “renewable diesel fuel, specifically hydrotreated vegetable oil (HVO) can provide the largest global warming potential (GWP) reductions for diesel craft provided the fuel is produced using waste feedstocks.”

It’s important to note here that HVO fuels are very different to the early iterations of biofuel that were prone to breeding bacteria (diesel bug) that can clog fuel filters and are compatible with many existing engines, including Yanmar’s YM series of two and three-cylinder units that were introduced 20 years ago.

Of course, many of us aren’t “average” users of our boats, so perhaps it’s better to reframe the question along these lines: who does electric propulsion and power work for?

Is there anyone who might benefit from a middle ground, with hybrid power?

And who are the people for whom an electric boat is not suitable until the way they use their boat changes dramatically, or a step-change in technology shifts the parameters?

Evolution of the electric boat

Many of the all-electric yachts I’ve sailed have been the result of customers positively asking for the new technology.

Typically these are early adopters who are happy to take an element of risk and, in some cases, even happy to help boatbuilders fund a prototype.

In my experience, this is by far most likely to happen at the higher end of the market for boats whose owners intend to spend extended periods of time on board, whether gentle cruising in the Mediterranean or more ambitious sailing across oceans.

At this level, choosing an electric boat isn’t simply about propulsion systems.

The big battery banks needed to power electric motors can also be put to good use in other respects.

Induction hobs and electric ovens use very little power compared to the electric motors needed to drive a yacht that may weigh 15 tonnes or more, while the same is true for electric outboards for tenders.

Eliminating the need to buy petrol for an outboard and gas for cooking, especially given all the different permutations of gas bottles and valves needed if you visit several different countries, certainly makes cruising easier.

Add in an efficient watermaker, plus the ability to recharge batteries from big solar arrays and generate 500-1,000 watts of power 24 hours a day from hydrogeneration (called regeneration by some manufacturers) while sailing and the boat therefore has the potential to be autonomous for very extended periods.

On a passage of several hundred miles such a boat might expect to motor, or motor sail through patches of calm, followed by periods sailing in good breeze.

With efficient hydrogeneration, the battery banks may be depleted and then topped up several times during the voyage, without the need to run the generator.

It’s also worth remembering that motor sailing in very light airs has the potential to be surprisingly efficient, especially if the destination doesn’t lie directly to windward.

This can give a very useful boost to speed, while drawing a remarkably small amount of power.

I’ve sailed a couple of designs around 45ft that, when reaching with mainsail and Code 0, have needed only a 3kW push from the electric motor – barely more than one-tenth of its rated capacity – to almost double boat speed, from a measly 2.8 knots up to a useful 4.8 knots.

What’s happening here is that a little extra help from the motor increases the apparent wind, so the sails develop more power and the boat goes faster, which in turn increases the apparent breeze still further.

Internal combustion engines, however, are not able to give such a gentle energy-efficient push.

Electric boat: Keeping cool

For those who sail in hot climates, air conditioning is also becoming an increasingly common option. In the past that usually meant running a generator all night, creating noise and vibration on board and disturbing neighbours in port.

However, with a big battery bank, it’s possible to run aircon all night without a generator, making it a game changer.

In this part of the market, there’s also a trend towards fitting huge amounts of solar power.

For instance, I’ve sailed both Fountaine-Pajot and Lagoon catamarans, each with more than 2kW of solar.

It’s even possible to fit a considerable amount of solar panels to smaller monohulls, which is far less expensive than in the past.

The electric version of Beneteau’s Oceanis 30.1, for instance, was launched with an option for almost 1kW of solar power.

The original idea behind this was so that the battery bank of a boat that is kept on a swinging mooring, with no access to shore power, could fully recharge between weekend outings.

A useful side effect, however, is almost unlimited electrical power when spending longer periods on board.

On a boat this size it would be almost impossible, at least in the summer, to use all this power with electric cooking, plus extensive use of laptops and entertainment systems.

Hybrid systems

Nevertheless, range restrictions mean there are relatively few all-electric boats outside the dayboat/weekender sector.

Instead, a hybrid solution is favoured with a very efficient diesel generator.

These are usually a relatively small unit that is sized to power the boat at around 5-6 knots in calm weather.

This can be a surprisingly effective option, as the generator can be run at its most efficient constant speed, which markedly reduces fuel consumption compared to conventional installations, where the genset is typically sized to cope with AC start-up loads, or a diesel propulsion engine that usually spends more than 95% of its life at speeds well below those that deliver optimal efficiency.

Apart from the AC, in many ways, this type of use isn’t that far removed from that of a bareboat charter yacht.

Granted, the crews might be different every week or fortnight, but the boat is still used almost constantly for several months of the year.

Charter companies are also more likely to look at total costs over a six or seven-year period than the upfront price.

If several mid-season oil changes can be avoided and refuelling on changeover day is easier, gas bottles don’t need changing every week and service batteries don’t need to be replaced every few years, then operating costs are reduced and each base is easier to staff and to run.

Large charter companies including Dream Yacht Charter and Sunsail are already making significant investment in yachts with hybrid systems including electric propulsion, efficient back-up generators, large solar arrays and the huge battery banks that make life on board much more comfortable and convenient.

Expect to see a lot more all-electric yachts at boat shows and on the water in popular charter zones and cruising areas that attract large numbers of large and well-equipped yachts.

Space saving

Given the popularity of day-sailers and weekenders with electric propulsion, it’s perhaps no surprise that the first boat with an electric auxiliary engine I sailed was the RS21, a 6.5m open dayboat with a strong racing bias.

There’s nothing new about fast raceboats with small engines – back in the 1970s J/24s had 2 or 3hp outboards to get back and forth to the start line, as do SB20s (the former Laser SB3).

However, the RS21’s tiny electric unit is a game changer that abandons the familiar form factor associated with an outboard engine in favour of a motor on the bottom of a diminutive daggerboard-shaped blade that’s easily lifted into a sailing position under the mainsheet hoop, along with a separate battery.

It’s a setup that reduces drag to an absolute minimum when sailing, yet makes the unit amazingly easy to deploy.

Importantly, this can be done safely from inside the boat, rather than hanging precariously over the transom.

The unit also has the benefit of being mounted well forward in the cockpit, so there’s far less tendency for the propeller to lift out of the water when the boat is pitching in waves.

With the standard battery, the range is 4-5 miles and there’s provision for a second battery.

Of course, such a system has to be designed from the outset to complement the boat and most of us are stuck with more standard formats that are available off the shelf.

Nevertheless, there’s one format that is useful for electric propulsion that can’t be replicated with an internal combustion engine.

This is the pod drive, in which the motor is attached to the outside of the hull. It’s a neat idea that can save a useful amount of cockpit or interior space and in most cases from a distance looks like a slightly oversized saildrive.

Surprisingly, sail inventory can have a big bearing on how suitable a boat is for electric propulsion.

Many recent designs sail surprisingly well in light airs if a Code 0 is used for reaching and an efficient spinnaker (asymmetric or symmetric) when the destination lies downwind.

Many of these are capable of reaching at almost the same speed as the wind in 4-6 knots of breeze, with the result that much less time is spent motoring in light airs compared to other craft.

Day-sailers and weekenders also score well in that they are also likely to be lighter boats than a serious cruiser and will therefore have more potential to perform well in gentle breezes.

This has two benefits for all-electric propulsion.

Firstly, it reduces dependency on the engine in light airs, saving the battery for complete calms, or using only a small amount of thrust when motor sailing.

This translates to more time spent enjoying a sail, without the din of a noisy motor.

A second benefit of a boat that’s intrinsically quick under sail is that it makes it feasible to sail fast enough in lower wind speeds to produce a useful amount of power through hydrogeneration.

The modest 1kW ePropulsion Spirit 1.0 Evo electric outboard, for instance, will generate roughly 20W at a speed of 4 knots, but hydrogenerator output rises exponentially with boat speed and this figure rises to 60W at 5 knots, to 95W at 6 knots and 200W when sailing at 8 knots.

Even though this energy is in effect harnessed from the wind, it’s not entirely free power and will therefore slow the boat a little.

This is most noticeable at lower speeds where frictional resistance predominates.

However, the effect reduces dramatically when close to hull speed and wave-making resistance is by far the biggest force holding the vessel back from sailing faster.

Coastal cruising with an electric boat

Even if electric propulsion can suit those spending extended periods on board, plus day-sailers and weekenders, what about the rest of us?

Coastal cruising can cover many different scenarios.

In some cases, each trip may be little different to those of a day-sailer or weekender, while others will involve significantly longer passages that are more akin to offshore sailing, even if the ultimate aim is to be moored up or at anchor overnight.

Many boat owners are governed by an imperative to return to a home mooring on a Sunday afternoon in good time for work or school the following day.

Even if distances are shorter, this is a very different situation to someone who’s able to spend several months on board and might happily sit in port or at anchor for extended periods waiting for perfect conditions before a long passage.

This means that, in addition to the greater distances that may need to be undertaken under power, coastal and offshore cruisers may also need to do so at higher speeds, or while fighting a strong tide.

Unfortunately, this will deplete an electric battery bank proportionately far faster than an internal combustion engine drinks fuel when running at high revs.

These scenarios for offshore and longer-distance coastal cruising can make electric propulsion look less attractive, even if that means giving up the big battery bank that can make life on board more comfortable and convenient.

For these boats, which may well not be used even every weekend during the summer, it’s also more likely that the most sustainable solution will be a diesel engine that can use HVO fuel.

Power vs range

Motorboats might appear to represent the biggest challenges for electric propulsion, but that’s not universally true.

Many RIBs for instance spend very little time at high speed, even in the unlikely event they are in use all day.

The RS Pulse 63 is a fully electric RIB that was originally developed as a coach boat for competitive sailing, but is now also available in commercial and leisure versions, as well as a superyacht tender.

A combination of a very efficient hull design, especially at speeds in the 10-15 knot range, and a light weight results in a boat that’s fast and yet has an impressive range.

It’s fitted with a 40kW motor that gives a maximum speed of 23 knots, while the 46kW battery bank provides a maximum range of around 25 miles even at 20 knots boat speed.

This increases dramatically at slower speeds: even at 15 knots it’s well over 40 miles and close to 70 miles at 10 knots.

And at five knots, range jumps to 100 miles, representing 20 hours of endurance and very low running costs.

While the RS Pulse is an attractive package, attempting to retrofit electric propulsion in a RIB originally designed for conventional power is liable to result in disappointment.

The primary issue is that drag would be far greater than that of a hull designed from the outset for electric propulsion, with the result that range and speeds would be greatly diminished, unless outlandishly large and expensive power units and battery banks were specified.

Although my primary interest is in sailing, I’ve always admired motorboats that harness technology in an intelligent way to produce an efficient vessel that’s fun to use.

Cowes-based yacht designer and builder John Corby created an elegant 20ft carbon fibre retro-style electric launch a couple of years ago.

The structure is of single-skin carbon fibre and weighs only 100kg, which is around half of the total displacement including batteries, twin Torqeedo pod drives, wiring and other systems.

I took it for a half-hour test run, achieving top speeds of around 12 knots yet when I returned to shore the batteries were still showing 90% full.

Pending a step-change in technology, larger motor cruisers with electric propulsion are likely to be restricted to displacement speeds.

Delphia Yachts in Poland has been owned by Groupe Beneteau since 2018 and now produces a range of seven 30-43ft (9-13m) displacement motor cruisers primarily aimed at inland waters, all of which are planned to be 100% electric by 2025, although currently they are also offered with internal combustion engines.

In contrast to most marketing of motor vessels, the brand makes a big deal of the benefits of slowing down in a quiet environment to enjoy nature and time with family and friends.

More competition, lower prices

As more people understand how to make the best use of electric propulsion, and the electrical gadgets and conveniences which can be powered with big battery banks, the more boats we will see that harness these technologies.

As that happens, upfront costs will fall thanks to greater take-up and bigger sales volumes, along with more competition in the market.

On the other hand, it’s unlikely to suit everyone for a long time due to the cost of retrofitting which means that the growth of electric boating is likely to mostly take place in new vessels for some time, even if some enthusiasts and trailblazers, such as Dan Deckert and Kika Mevs of YouTube channel Sailing Uma, continue to upgrade older boats with electric motors and large battery banks.

Nevertheless, a lot of money is being invested in this sector and we can expect to see constant changes that will expand the market.

Yanmar, for instance, has just announced a range of electric units that combine a motor with the battery and saildrive.

These fit onto existing Yanmar engine mounts, vastly simplifying the process of repowering with an electric unit for many boat owners, while also streamlining production processes for boatbuilders who want to offer both electric propulsion and conventional diesel engines in the same model.

Dufour and Fountaine Pajot have also announced a move to what they call a Smart Electric concept, which takes a holistic view of all the systems that use electricity on a yacht fitted with electric propulsion and has an efficient backup generator.

The system was developed by fellow La Rochelle-based company Alternatives Energies, whose background is in developing solar-powered ferries and water taxis and which is now owned by FP.

Interestingly, it has greatly simplified the system compared to many, which ought to help reduce installation costs, as well as streamline maintenance and troubleshooting.

A combination of using a higher voltage than usual in the leisure side of the industry, along with pod drives that are immersed in the sea, means the motors don’t need to be water-cooled.

Until recently there were only two main players in the marine market for electric propulsion, but that’s now changing and we can expect to see a broader range of technical approaches as the market becomes larger. Watch this space…

Electric outboards

Today, sales of electric outboards for tenders are strong, while demand for small petrol outboards is declining.

Electric motors for this purpose are far smaller and lighter than a conventional outboard, which makes them far easier to handle.

And a single battery charge can last for several typical trips back and forth to a mooring, without the hassle of finding, carrying and storing petrol.

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