Silent running

In general terms, the electric boat market is forecast to grow from around US$8bn in 2024 to US$20bn by 2032,” says Leif Stavøstrand, CEO of the Norwegian motor manufacturer Evoy. His figures are based on a global report by Credence Research, and confirms that the sector has a bright future, especially as the technology evolves. “The compound annual growth rate (CAGR) is expected to be about 12.5%,” Stavøstrand continues. “Europe and the United States are at the forefront of this growth, which is galvanised by increasing demand for sustainable alternatives, advancements in battery technology, and government initiatives that incentivise zero-emission practices. We’re seeing more players in the electric market, as well as a steady increase in consumer adoption. These are both influenced by factors including the acceptance of technology and growing trust in electric solutions.”

Evoy, which has recently partnered with the electric fitout specialist Vita, is a dominant force in the high output space, with a strong market in the demanding commercial sector.

“Evoy Vita’s electric motor systems have redefined what’s possible for electric boating,” Stavøstrand says. “They now deliver power parity with ICE (internal combustion engine) systems. The market evolution here is a shift in consumer perception, particularly in the recreational sector, where electric boating is gaining traction.”

A tour of the halls of the recent European winter boat shows, Metstrade in November and Düsseldorf in January, confirms that electric drives for leisure applications are on a roll. Long established brands are facing competition both from well-funded startups, and from some leading combustion engine OEMs, who are also anticipating a fossil-free future. Good examples of this diversification are Yamaha, with its revolutionary hydrogen engine and Brunswick’s Mercury Marine, with its Avatar range of electric outboards.

Meanwhile, the boating public, many of whom now drive hybrid or all-electric cars, are discovering the pleasure of near-silent running. (We say ‘near silent’ as an electric outboard still makes some noise at speed). Minimal annual service bills and a complete lack of exhaust fumes are also encouraging a greater take-up of electric drives. So far, the only real barrier to buying a medium to large electric outboard is the capital cost, especially as all the ‘fuel’ for the next few years must be bought in advance. This can double the price of an already quite costly motor. Despite an expensive battery system (although prices are steadily decreasing due to economies of scale), range is still limited between charges. However, it is being extended by a combination of more efficient batteries and motors, the harnessing of onboard renewables, more accurate monitoring and in some cases the use of hydrofoils.

Perhaps the biggest takeaway from the shows is how the choice of design and horsepower is broadening out. This is being helped by the automotive industry, emboldened with a clear future for electric-only and with technology that is packing ever more horsepower into an ever-decreasing footprint. Unlike a combustion engine, which is around 35% efficient, a modern electric motor converts around 90-95% of its stored energy into ‘work’. On average, they will deliver between

5.0-8.0kW/kg (2.9-4.7hp/lb), which is a very useful power-to-weight ratio, especially when it comes to portable outboards. With electric motors also being created for the aeronautical sector, that ratio is getting even better. For example, a recent concept design by the Massachusetts Institute of Technology (MIT) is expected to deliver 17kW per kilogram (10hp/lb), or one megawatt (1,300hp) for around 125lbs. That’s enough to make an electrically powered short-haul airliner feasible. Meanwhile, compact, high-output automotive motors continue to be adapted for marine use, mainly by modifying the cooling. This has been demonstrated by the ‘pancake’ axial flux motor design usually found in car wheels, and now successfully used in the Propel outboard from UK-based Saietta.

Design ‘from the bottom up’

Unlike an internal combustion engine, which requires the manufacture of hundreds of moving parts, an electric motor is relatively simple. This has encouraged entrepreneurs to develop several sleek and stylish designs without the need for massive investment in machine tools. There is even a growing market for converted mass-produced ICE outboards, where the combustion head is removed, and the chassis and gearbox repurposed with a variable-speed electric drive. Stealth in the US and Rechargable Boats in Australia have both identified this niche and are producing outboards that are fully compatible with existing transom arrangements. They can also access mass-produced consumables such as anodes, seals and propellers. For other OEMs, and several startups, advanced design software and off-the-shelf components are allowing them to create electric drives literally from the propeller hub upwards. The results are impressive, with several winning prestigious design awards in the process, particularly for sustainability.

Such is the versatility of the electric drive that the definitions of what is an outboard, a thruster, or a steerable pod are beginning to blur. Who would have thought, for example, that you could mount a propeller on a hollow tube filled with batteries? The French company TEMO has not only developed this portable type of ‘pole’ or ‘wand’ drive, but the design is selling well around the world. In fact, sales have been so good that the company has recently announced a new US distributor.

For this Spotlight, we have focussed on what is new within the ‘traditional’ outboard sector, namely a transom-hung motor that can be lifted clear of the water and detached from the boat. Even then, there is some crossover, but this all means the boatbuilder has a lot more options to electrify their product.

1. What’s new – Larger outputs

Larger horsepower ratings have been available for some time thanks to the transport industry, particularly the electric drives developed for heavy goods vehicles. Although this can lead to a more complex installation involving advanced cooling and control electronics, not to mention a monster of a battery, the big advantage is the versatility of the installation. Joining the stalwarts of Evoy, ACEL, Explomar and Vision, two recent launches – and two teasers – caught our eye.

EP technologies’ Falcon

A new outboard from the Danish e-drive specialist EP Technologies has been designed with the boatbuilder very much in mind. Named after the Peregrine falcon, a bird that can reach over 390km/h (200mph) on a hunting dive, the new motor is also designed for performance. The Falcon is currently available in two variants, one offering 130kW (peak 200kW) on a 400-800VDC architecture, and the other rated at 230kW (430KW peak) on a 550-850VDC platform. That equates to 169hp and 299hp respectively.

Showing the new outboard at Metstrade 2024 in Amsterdam, CEO Marcus Ottiker explained that the motors had been designed exclusively for electric propulsion, rather than modified from an existing chassis. As such, whilst they could still be mounted in the traditional way, the design offered a compact unit that optimised onboard space for additional batteries. There is also less weight on the transom, a saving of around 100KG (220lbs) compared to an equivalent combustion outboard.

The key element of the new Falcon is the steerable lower leg, whilst the upper section remains fixed. This isn’t a new concept in electric outboards, but EP Technologies have strived to make it as customisable as possible.

The motor and electronics are all housed above the water, and locked at 90 degrees to the transom, whilst the drive hub is immersed and fully steerable. This keeps the sensitive components fully protected, whilst the propeller can be directed through a full 360^o of arc, allowing for exceptional handling.

EP Technologies works closely with boatbuilders to provide the Falcon as an easily installed package, including custom shaft lengths and matching colour schemes.

A two-circuit cooling system is integrated into the leg with a mechanically driven impeller pump, so installation is said to be easy. After clamping the engine on, the installer simply needs to connect two high voltage cables and a CANbus control wire.

Seabird 400X

Already well known for its foiling all-electric E1 race boat, Seabird Technologies has now presented its new outboard to the boating world. Badged as the 400X, the new drive is as sleek as they come, boasting a continuous power of 300kW (400hp) with a peak of 400kW (530hp). The motor is based on an 800V architecture but only tips the scales at around 200kg (440lbs). The electric motor is encapsulated in a torpedo-shaped hub, whilst the electronics are kept within the slim leg and cowling. The outboard can turn to 45^o each side of centre and has been designed from scratch to compliment the stern of any fast, planing motorboat.

Esea PD100

Heralded as having the ‘highest compacity ratio of electric outboards’ the PD100 from Menorca-based Esea is aimed directly at the builders of small, high-speed runabouts. In 2021, the team of young entrepreneurs and engineers set out to develop a new, fully electric drive system that offered greater power in far less space. The result was a low profile 75kW (100hp) outboard designed to allow seating to slide over the top of it. When in the raised position, the motor doesn’t intrude into the living area, and when deployed, the cockpit can be lengthened, giving the boatbuilder plenty of space-making options. The drive leg is spilt in two, with the lower half being steerable through 180^o to provide a high level of control. The maximum voltage is 500VDC, with the P100 weighing 95kg, excluding the battery. Whilst still in the startup phase, the new design looks promising, and although not entirely original in concept, it offers a great deal of versatility in design.

2. What’s new – Mid-range

The real advantage of the compact, brushless direct current motor (BLDC) is that it can be housed above or below the waterline, and as part of an assembly that can be broken down into modular parts for easy transport. Two new engines have taken full advantage of the portability aspect, with some clever practical modifications.

Zparq

Pronounced ‘Spark’ this new 10kW (claimed as 15hp equivalent) electric outboard from Sweden features a new type of motor that is fully scalable. The company says that the Zparq is currently the lightest 10kW outboard in its class on the market, weighing just 17kg (without the electric trim mounting bracket). The modular 2.8kWh 48V batteries are designed for plug and play installation, ergonomically designed for easy transport. Two modules, weighing 20kg each, are wired in series to create a 96V architecture (2x48V) each, with a combined 5.6kWh capacity. The most intriguing aspect of this new outboard, however, is the design of the electric motor, with larger outputs planned. The team has patented a Hyperflow’ cooling system allowing the motor to sit outside the usual torpedo-style of watertight casing. Instead, the water is allowed to flow through the heart of the assembly as well as along the outside, bringing better cooling to the windings to give greater efficiency. (Higher operating temperatures lead to increased internal resistance, so motors need to be kept as cool as possible when working hard.)

With the advantage from starting literally with an idea, the technical team has created an entire system based on their new motor. A dedicated app not only keeps a close eye on the charge/discharge levels, including anticipated range, it also acts as a portable chartplotter. The Zparq will be available for retail sales from the spring of 2025, and the company is actively recruiting distributors.

Zero Jet outboard

Developed from a successful electric waterjet design, the 18kW (25hp) Zerojet outboard uses the same electric motor, but with an internal belt drive to a conventional propeller. Built in New Zealand, the new outboard is claimed to be the lightest in its class at 38kg and connects to a separate 48V DC battery. In a departure from some other OEMs, the outboard can be coupled to any third-party 48V lithium-based marine powerbank such as those from Mastervolt, Victron or Kriesel. Zerojet supplies the necessary power adapter, prompting one Metstrade visitor to remark, ‘how very un-Apple of you’. The company’s standard proprietary battery is lithium iron phosphate (LiFePO4) at 10.4kWh and gives about two hours of run time, assuming average use.

With similar engineering to the successful jet rib, the motor features a closed loop oil-based cooling system with a heat exchanger in the leg, so no saltwater meets the internals. The carbon-fibre belt helps to reduce any transmission noise and is easy to replace. Zerojet has also opted for a conventional propeller, allowing boaters to pick up a mass-produced spare from any outlet, or experiment with different types that fit a standard spline.

Neil Mans, Zerojet’s co-founder, explained that they initially thought the electric outboard sector was quite crowded, but discovered a space in the 25hp range, so decided to adapt their already proven technology to fill the niche. The idea was to have a lightweight but stylish motor that would weigh less than a conventional 25hp ICE engine, which usually takes two people to lift. The new Zerojet model can be carried by one (relatively fit) person, and when combined with the battery pack the whole installation weighs about the same as an equivalent four-stroke ICE. Zerojet says it is researching some larger outputs and has produced some ‘very exciting figures’ in terms of power-to-weight ratio.

Momentum M10

Also targeted at the lower end of the mid-range sector, but also keen to remain portable, is the new M10 from Singapore-based Momentum. The 10kW (13-15hp) outboard features a submerged and sealed motor with a built-in reduction gearbox, and a choice of aluminium propellers. The motor is married to a proprietary 6.4kWh 72V battery, the MB6 which is sized to fit into a typical RIB’s fuel locker. Because the battery is above the ‘danger-to-life’ 50V threshold, it has been built to be extra safe when handled. Even when switched on, the battery sends no power to the connector until it is physically plugged in to the outboard. Even then, nothing will happen without the magnetic kill switch. This is to prevent possible shorts or electrocution if the plug is dropped into a wet bilge.

Another clever idea is to do away with fault codes. Rather than a number appearing on the control screen, the issue is explained in plain language, to help the operator know what is going on without referring to a handbook. The bracket has also been thoughtfully designed with a simple release lever that pulls inwards, and which is easy to lock. This allows the bracket to remain on the boat whilst the outboard is taken ashore.

Under 10kW sector

The smallest end of the outboard sector has had a few additions recently, with some earlier concepts reaching the production phase and a few tweaks to some old favourites. Ergonomics and portability remain key trends, but we are also seeing a few interesting additions, such as keycode access, trim and tilt and some quite sophisticated apps.

Ion 6kW and Tohatsu Alaris 6.0

Built in the US by Ilmor, the Ion has had some new additions after its first appearance in 2023. On display at Metstrade was the latest design of this futuristic looking outboard, now with a new tiller version with built-in touch screen. The submerged 6kW motor is based on a 48V architecture and has a proprietary - but optional - 4.4kWh battery. (The company says the Ion is ‘battery agnostic,’ and is happy so long as it has the right voltage). The battery is sealed to IP65 (splash proof) and has several built-in features including fast charge capability.

The outboard has an integrated hydraulic trim and tilt, said to be the only type in its class, and features a stylish RGBW LED strip on the cowling. This turns to bright white to act as a stern light when underway.

As an additional safety feature the motor has a combination keypad to switch it on, a good anti-theft deterrent. Three shaft lengths are available, 63.7cm (25in), 76.4cm (30in) and 88.9cm (35in). There is also a choice of two propellers, and tiller or wheel steering. Ilmor has recently announced a joint project with Tohatsu to develop a 6kW motor (roughly 8hp). The result, the new Alaris was shown for the first time at boot Düsseldorf, and based on the Ion’s motor and control system.

General trends

1. Speciality or standard propellers?

There seem to be two schools of thought when it comes to propellers. Some OEMs want their customers to access the wide range of existing ‘standard sline’ propellers, whilst others want to optimise the propeller to squeeze every ounce of thrust from the motor. Existing ICE outboards that have had the combustion powerhead replaced with an electric alternative tend to retain the original propeller design, although often optimised for a different torque curve, but newer designs and start-ups tend to go for their own proprietary props. For those OEMs who want to supply specialised propellers, the emphasis is on performance. Zparq, for example, has partnered with AB propellers to develop a small blade, high twist version, whereas Torqeedo has added a propeller boss attachment to harvest ‘swirl’ energy. Momentum offers a choice of props, such as a four-bladed high thrust version for sailing boats.

Another consideration is the ability hydro-regenerate when a boat is under sail. Several outboard OEMs are building this facility in, even though it can lead to a few more compromises in the propeller design. The popularity of sleek monohulls and fast catamarans has made the recovery of some useful power from the wake a viable option. ePropulsion, for example, estimates its Spirit 6.0 outboard can generate about 1kW at a sailing speed of more than 6 knots.

Rim drive propellers

A system that is becoming more popular with electric outboards and thrusters is the RIM drive. A pioneer of this type of system is the Netherlands based company Rim Drive Technology (RDT), which has produced two new outboards, the Entry Level and the Steerable (due to its 360^o steering arc.).

In a rim drive, the aluminium outer housing contains the electrical windings that form the stator, whilst the magnets are held within the inner housing called the rotor. The rotor also supports the inward-facing blades. The electrics are all potted in epoxy to keep them completely watertight whilst the ceramic bearings are water cooled.

“A Rim drive motor has several major advantages as compared to a normal propeller,” says RDT’s Nop Beursken. “A major one is that there is no central shaft, which avoids the common issue of entanglement. This increases the operating time and stability. When combined with other benefits such as less noise, reduced maintenance and a ‘pressure neutral design,’ this made the choice very clear for us. The blade profile has been specifically designed for this type of motor, with no cavitation when operating under normal conditions. Due to the capped end of the blade the propeller noise is significantly reduced. As the most effective part of the blade is the outer portion, nearest the housing, so the inside of the blades can have a more aggressive twist. They can also be thinner, which increases the blade efficiency.”

For OEMs that have specific requirements, such as wanting more thrust at lower speeds, specific designs of blade can be accommodated.

“The propeller can easily be replaced by the user,” Beursken says. “We can provide a custom version if specifically requested, or the customer could design their own.”

2. Greater portability

The ability to split an engine into modules helps to make them far more portable, but designers are now paying a lot more attention to the provision of suitable handles and ergonomics. The ability to break an engine down into separate modules makes carrying a higher-power unit much easier.

 

3. Better range calculation

With range anxiety still a factor in electric boating, although less of an issue than before, many OEMs have developed far more accurate monitoring systems to keep the boater fully informed of remaining distance. Some, like Evoy, have a protocol that keeps a reserve to run a fast, planing boat at around 5 knots. This provides an extension to the range to get the boat home without battery damage. Here are some of the latest developments.

RAD and Savvy Navvy’s Smart Range

Electric outboard makers RAD and the IT tech company Savvy Navvy have come together to integrate power management with precision navigation. The idea is that owners of RAD outboards will have access to some of the most accurate range and routing data available, greatly helping with passage planning and range expectations. Often, a motor manufacturer will supply their own range data via the battery management system (BMS) with companies like Torqeedo pioneering an app that places a range ring onto an electronic chart. Reducing speed will allow the ring, centred on the boat, to extend outwards. What Savvy Navvy has done is take this concept a stage further and add in the variables, such as adverse wind, sea state and tide, whilst also calculating the most efficient route. As the environmental conditions can make a big impact on battery drain, the new Smart Range technology should give boat owners much greater peace of mind.

The founder of Savvy Navvy, Jelte Liebrand, says he was confused by the amount of data available to help with navigation, so developed a system where it could be condensed and presented on a device a boater would always have with them, their mobile phone or tablet. The tie-in with RAD is part of his firm’s new Savvy Integrated system, launched in late 2024. This platform has been designed for boatbuilders worldwide, and is compatible with Android, IOS, PC and Mac.

4: Proprietary battery or agnostic?

For the makers of electric outboards, there is one major question. Do they supply a dedicated ‘proprietary’ battery that only works with their motor, or do they become ‘battery agnostic’ so the customer can use whatever they want? There are pros and cons for each, and some companies have stayed firmly in one camp or the other for the duration. Hong Kong-based OEM ePropulsion, for example, only ever specifies its own brand batteries, as does German company Torqeedo, whereas US-based Elco says customers can hook their outboards up to anything of the right voltage, and of any chemistry. Some, such as US-based Ilmor and New Zealand-based Zerojet, give the option for both.

5: Touch safe or high voltage?

Should you be unlucky enough to touch any live DC connection below 50V, the chances are you will live to tell the tale. The human body has enough internal resistance to stop the shock from being fatal – usually, anyway. Another big advantage is that marine technicians don’t need specialised safety training to install a sub-50V system, so their usual electrical skills will suffice. As a result, many OEMs seek to keep their marine drives under that important threshold.

The US OEM Stealth has allowed boatowners to change voltages whilst retaining the same motor.

“The Stealth 50HP and Stealth 75HP have been replaced by the Stealth Switch,” says CEO Scott Masterson. “The Stealth Switch will operate with a battery pack voltage range from 48VDC to 144VDC. This makes it possible to choose from a variety of battery sizes to tailor the users need for performance and budget. For example, the customer can start with a single 48V battery and produce 12 horsepower, then simply add more 48V batteries in series to make more power. Two 48V batteries in series will create a 96V pack to operate at 25 horsepower. Three in series can be added for a total of 144V, producing 35 horsepower. With a 144V battery, the Stealth Switch can produce a maximum of 75 peak horsepower and 35 continuous horsepower. The best part is that no changes need to be made to the Stealth Switch, just add more batteries for more power!”

Looking ahead

“Suppliers are now aligning to in the race towards a ‘green’ ocean with electric propulsion,” concludes Evoy’s CEO Leif Stavøstrand. “This is being driven by the underlying megatrend towards electrification due to its inherent performance and experience superiority. Gradually, battery improvements on energy density and price reduction will roll out step-by-step. Features such as autonomy, V2G (vehicle to grid) and an enhanced user experience – through better user interfaces in screens and apps – will also continue to spur electrification. The digital connectivity and plug-and-play features Evoy provides through its proprietary software and motor systems are continually maturing, enhancing both system usability and long-term reliability.”