Electric boat motors arising from work on the high speed flywheels of Formula 1 car racing are being launched by the UK’s Equipmake. The company already supplies their APM line of electric motors and drive trains to automotive OEMs, specialist supercar manufacturers and electric buses, and sees a lot of opportunity in marine electrification.
Equipmake Managing Director Ian Foley says “The benefits – high power density and light weight, combined with an extremely compact package – are just as relevant to the world of marine. Plus, they are easily adaptable to power anything from a hybrid luxury yacht to hybrid tugs to all electric RIBS and sport boats.”
Electric boat motors keep magnets cooler
The two motors being introduced to the electric boat world are the APM 120 and APM 200, permanent magnet (PM) motors that use a spoke architecture to give them a major cooling advantage over other PM motors.
There are lots of good reasons for using permanent magnets in a motor, but one of the limiting factors is that the materials used – commonly neodymium as in the Equipmake motors – have maximum operating temperatures and don’t respond well to overheating.
Most PM motors are constructed using laminating to embed the magnets in the rotor (rotating part) of the motor. They are usually set up in a shallow V formation, as in the motor on the left in this simplified schematic. In the APM spoke motor on the right, the magnets run right through the hub, meaning the water/glycol in the cooling jacket (blue) can get closer to the magnets and keep temperatures down.
That allows higher speeds, longer running times, and the lower temperatures also cut costs, as a less expensive type of neodymium can be used for the rare earth magnets.
High power and light weight
These advantage of spoke motors have been known for awhile, but the problem has been how to manufacture them in mass production quantities. Foley told Popular Mechanics in 2018 “that’s the bit we’ve solved.”
Foley has solved a lot of things over the years, especially in car racing. He got his start developing the active suspension system for Lotus in the late 1980s and then worked on a paddle shift gearbox for Le Mans race cars in the 1990s. The forerunning work on the APM motors, though, was Formula 1’s kinetic energy regenerative braking system (KERS) which he developed for Williams-Toyota in 2009.
The flywheel captured energy that would normally be lost as heat when a race car brakes, spinning at up to 36,000 RPMs to perform its function. Coming out of the braking the kinetic energy stored in the flywheel would be converted to electricity to provide a power boost to the electric motors in the Williams hybrid car. In looking at the components, Foley realized that the flywheel could form the basis of a lighter, more powerful electric motor.
The APM 100 has a maximum speed of 12,000 RPM, and the APM 200 a maximum of 10,000 RPM, with the spoke architecture and cooling system being key elements in enabling the motors to run at those speeds for long periods.
Both motors have an integrated planetary gear system that brings the propeller speed down to about 2000 RPM. The integration of the inverter also helps keep the whole package small and light.
The APM 120 weighs 14kg /31 lbs and is 200mm / 7.9″ long with a diameter of only 170mm / 6.7″. The peak power is 125kW and continuous power is 75kW. Power density is not a measurement commonly seen, but the rating for the APM of 9kW per kilogram is impressive.
For the APM 200, the figures are: peak power: 220kW, continuous power: 110kW, weight: 40kg / 88 lbs, length: 247mm / 9.75″, diameter: 318mm / 12.5″ and power density of 5kW per kilogram.
Packing more power into less weight is key to electric boating’s future, but a lot of the work is focussed on batteries, especially the development of solid state technology, new chemistries like lithium sulfur or coatings that help improve energy density. Maybe the future is getting energy dense batteries and motors working together.
Off the rack or custom solutions
Equipmake just opened an all-new UK factory that has facilities to design, test and manufacture everything from motors to fully electrified platforms. When providing complete drivetrains they work with different lithium-ion battery suppliers to provide the best solution for the application.
Foley says “There is no doubt that the electrification of the marine industry will accelerate rapidly in the coming years. Our APM models can provide a cost-effective, rapid route to an electric future, and we can work with almost any marine business to create an entire, tailormade electric powertrain.”