The electric outboard revolution
Jake Kavanagh looks at how the burgeoning electric outboard market is paving the way for more widespread electric propulsion
The market for electric outboards has been growing fast over the past few years. Boat owners love the idea of silent, fume-free cruising using lightweight motors that will have a long service life. Standard propellerdriven outboards are still the biggest sellers but there are new designs that can convert electric power into thrust with up to 96% efficiency. The initial purchase price is still high, but the motor will gradually pay back over the years in saved fuel, service costs and consumables.
“With an electric outboard, there’s not much to go wrong,” says Nathaniel Evans, a sales engineer with Golden Arrow Marine. As an agent for the German-made Torqeedo range (now part of Duetz) Evans also looks after customer service but admits it’s a quiet desk.
“The motors are sealed for life, and the batteries can last for over 2,000 charge cycles. The only time we have to strip an outboard down is when it has been damaged, usually by hitting a submerged object. If the impact is hard enough, it can break a seal and let water in. But apart from that, the brushless motors require almost no servicing at all. If the dedicated battery packs are properly looked after, especially when it comes to long-term storage, they give faultless service too.”
According to
Evans, portability appears to be a major factor for customers buying a Torqeedo outboard. “Boaters love them,” he said. “There are just three components – the motor, battery and controller, all of which are relatively lightweight. This appeals to the older generation of boaters who want something dependable and highly portable.”
While smaller electric outboards can have a higher purchase price than an equivalent 4-stroke, Evans points out that they also have none of the ongoing costs. “The fuel can come from renewables, and there is no servicing or winterisation needed. Also, no storage issues with sump oil. This is all helping to drive sales.”
Another big advantage is longevity, a
subject that US-based Stealth Outboards is keen to promote. “There is little or no obsolescence with the outboard,” says MD Scott Masterson.
“Many of us wish our old petrol 40hp outboard still ran as great as it did on the day it was new, like electric does. Electric motors are rated in thousands of hours of operation, not hundreds. Resale values for electric outboards are excellent and used motors are well sought after. As batteries become lighter, more powerful and affordable, this industry will explode.”
Even quite powerful e-outboards are still easy to lift on and off a boat, especially when the battery is a detachable unit. As most proprietary batteries are lithium-ion, they are usually around three times lighter than a lead-acid equivalent anyway.
As a result of more dependable and ‘smarter’ motor technology and steadily improving battery chemistry, yacht owners who have converted to electric-only propulsion – even if just for the tender – usually endorse their decision. The experience with the cleanliness and silent running of the outboard often encourages them to consider electric propulsion for the yacht itself.
As TEMO’s Alexandre Seux explains: “Few boaters will invest r10,000 for an electric propulsion system for their yacht until they are fully confident with the technology. Instead, they will start with dinghy propulsion, but only once they are convinced by its advantages will they invest in higher power for their main boat. I believe the dinghy market will drive the growth of the entire e-propulsion market in the yachting industry. That’s why at TEMO we chose to start small and every year we will unveil a more powerful system.”
Battery power problems
Battery range, battery price and recharge times are the main stumbling blocks for electric power in the general marine market. Per kilogram, battery chemistry is lagging a long way behind the energy density of fossil fuels but is steadily catching up. This drawback is being offset by much smarter control systems to eke out the amps.
The price of lithium ion, which is lightweight and can be repeatedly deep cycled without negative effects (unlike ordinary lead-acid), remains high, however lithium itself is becoming cheaper due to economies of scale.
In the automotive sector, leading
companies such as Tesla, Honda and Volvo are pushing ahead with research into chemistries that can accept rapid charging. No-one wants to sit on a garage forecourt for more than a few minutes while refuelling.
Meanwhile, shipping is exploring long-range alternatives as the world’s merchant fleets attempt to become emission free by
2060, the hydrogen fuel cell being a clear leader
How much power?
The output of the internal combustion engine is usually rated in horsepower. How that horsepower is harnessed depends on the gearing and the prop. Some petrol outboards are deliberately configured to drive a small yacht, with the prop pitch and gearing differing from a similar horsepower model intended to drive a tender.
A lot of that changes when it comes to electric outboards. The industry will still talk in terms of horsepower equivalents, but electric motor output is always given in kilowatts (kW).
The basic conversion is 1kW = 1.34 horsepower.
Submersible motor-type electric outboards will operate without a gearbox, which is a key advantage. The power is direct and totally controllable, with no minimum revs needed to prevent a stall. The drive can also go from full ahead to full astern almost instantaneously, which can be extremely useful.
Battery capacity is the main factor to be considered when choosing the right outboard. The more power you have, the faster you can go (hull shape permitting) but the shorter the range. When it comes to electric outboards, they’ll usually be powering a relatively small craft with limited space to store the batteries. On a tender, the battery pack may even be a detachable part of the motor itself.
But, as Aimid Lazaaoui of Dutch-based Elva remarks, a limiting factor in highspeed, larger horsepower electric motors will be the ability to fast charge. His company produces outboards up to 3.5kW, with inboards of up to 9kW, but still sees most growth in the lower-powered cruising sector.
“The bigger the motor, the more charging power you need,” he says. “The average residential socket provides 16A at 230V, which can recharge a system of up to 3.3kW. But for larger capacities you’ll need specialised fast chargers.”
Calculating horsepower
The real output of any engine is the actual thrust delivered at the propeller. As such, care has to be taken when comparing the output of electric outboards against petrol equivalents. Beware of systems rated at ‘10kW’ when this actually refers to the kilowatt hours (kWh) of the batteries.
“We use a basic formula to determine real power on the shaft,” says e-Tech’s Norbert Fryca. “This is calculated by using input power from batteries multiplied by
The motor is either sealed in an underwater casing, or housed above the waterline under a cowling, as in a standard petrol outboard.
Keeping the motor below the water helps with cooling and makes an already quiet engine virtually silent. The downside is that it is more vulnerable to water ingress if the seals get damaged.
Above the waterline the motor is easier to access, but the transmission is via a gearbox rather than direct drive so there will be some efficiency loss and a little more noise. However, this configuration allows much larger motors to be installed as no submersible casing is required.
Example 1: Mitek
Italian-based Mitek makes a series of outboards where the drive is enclosed under a cowling and the power is fed in from a separate battery bank.
“Our outboard sales are focused on the portable market, from 2.6hp up to the newest 15hp and 20hp,” says sales manager Silvia Peduto.
“Mitek outboards look familiar on the outside with a classic ultra-tested construction, but the inside is a completely different story. We have efficiency above 90%, a high and constant torque and lighter weight. The status of the motor and batteries is digitally under control on your phone. I would say that real innovation lies in higher efficiency and simplicity. All our products are designed to simplify our lives without compromising our ecosystem.”
Example 2: Torqeedo Travel
The German-made Torqeedo 1103 Travel typifies a design where the motor unit is submerged. This 1kW motor is roughly equal to a 3hp petrol outboard, but with the obvious limitations of range. The
1103 nomenclature refers to the 1100W battery, which is detachable and weighs 17kg (37lb).
Torqeedo was arguably the pioneer of lightweight electric outboards but is now facing some stiff competition. As such, it has been refining existing models and producing new ones, with the redesigned 603 model (left) out in 2021. Both motors are IP67 waterproof, meaning you can immerse them to 1m for 30 minutes and they’ll still work just fine. The control handle contains a built-in GPS and has an LCD display showing charge state, speed, estimated range and energy draw. The new generation of motors are exceptionally quiet, as earlier models were known for a distinctive whine. Now, thanks to new technology, the motor is described as ‘little more than a human whisper’ when under way.
Example 3: e’dyn
A co-operation between Slovenian-based Podkrižnik and Italian-based e-concept, e’dyn is a good example of futuristic design and lightweight construction. The motor is housed conventionally under a cowling and fed from a separate battery bank. A new ‘Free Time’ line of 2kW, 4kW and 6kW models will be available from 2021. e’dyn is also upgrading its popular 11kW model with a new communications protocol and a 25kW version will be available shortly. As with most modern outboards, energy management is a priority.
“We saw lack of customisable options in our old design so we are working on more open protocol-based systems that are user friendly,” said project manager Tomaž Murko.
“In the future there will definitely be significant improvement in battery chemistry and power management. With our new systems we will be able to replace old technologies or make small optimizations such as communication signals without a problem”.
‘Battery capacity is the main consideration when choosing the right outboard’