One of the world’s biggest petrol engine manufacturers has launched its first electric drivetrain. We take a look at the Yamaha Harmo...
The new Yamaha Harmo electric boat drivetrain may be a rather modestly powered 3.7kW motor, equivalent to a 9.9hp petrol engine, but it is being seen as a major statement of intent from the Japanese brand synonymous with big, powerful four-stroke outboards.
None of the other big outboard manufacturers (Mercury, Suzuki and Honda) have yet embraced the move towards electric motors.
Intriguingly, the Harmo is neither an outboard engine nor a sterndrive but a new propulsion package that borrows ideas from both camps.
It is mounted on the transom just above the waterline much like a sterndrive leg, but in keeping with the outboard engine ethos it’s an entirely self-contained unit that includes the motor and steering mechanism.
The only through-hull fittings are for the electric cables connecting it to the battery, steering and throttle head. A sturdy top hinge allows the whole unit to tilt 74° up and out of the water when not in use to prevent fouling and corrosion.
Rather than having an exposed propeller with a central hub drive motor, the Yamaha Harmo uses a unique rim drive mechanism that sees the propeller enclosed within a protective circular casing.
This is made up of a wide fixed outer ring of coils, through which the current passes, and a narrower rotating inner ring of magnets to which the four slender propeller blades are connected.
When current is applied, the inner ring spins, turning the blades and propelling the boat forwards. Yamaha claims this is a quieter, more efficient solution than a traditional hub drive motor, generating high thrust at low revs with fewer moving parts.
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This in turn leads to reduced frictional losses and increased reliability. It also has the advantage of protecting the propeller tips from floating debris or groundings.
Three fixed vanes behind the propellers help direct the thrust for increased directional stability as well as enhancing safety for those in the water.
The other unusual innovation is the steering mechanism. Rather than the whole unit pivoting from side to side like an outboard engine, only the lower half moves.
Again this has a number of benefits. First, it means that the drive can be integrated more neatly into the design of the transom without having to leave space for its steering arc.
Look at the photos of the boat it’s fitted to and you can see how little clearance there is between the drive and the two bathing platforms either side of it.
Second, the Yamaha Harmo allows for a much wider range of steering angles as the lower unit is small enough and far enough away from the transom to swivel 140° from side to side.
At full port or starboard helm it effectively acts like a stern thruster, pushing the stern almost directly sideways rather than relying on the less acutely vectored thrust of an outboard or sterndrive.
To make the most of this ability, the Yamaha Harmo comes with a joystick control as well as a smart looking digital throttle and engine control unit.
It will be interesting to see how well this works on single engine set-ups without a bow thruster to keep the front of the boat in check but in twin set-ups it should make for effortless sideways manoeuvring on and off a pontoon.
Yamaha Harmo: Batteries not included
As a single installation it is suitable for craft up to 21ft while a twin set-up can cope with boats up to 32ft.
The speed and range will depend on the design of the craft and the size of the battery installation. Its 48V operating system can run off either lead acid or lithium-ion battery packs depending on the cost and packaging requirements.
At the moment the emphasis is on the European market where its silent, emissions-free nature is likely to appeal to manufacturers of lake and river boats, but the Yamaha Harmo will be introduced to the US in 2022 as well.
No prices have yet been announced. It may only be a tentative first toe-in-the water exercise for Yamaha, but for an outboard engine manufacturer of its size and reputation, the Harmo could prove to be an extremely significant one.
Yamaha Harmo specifications
Motor: 3.7kw (equivalent to 9.9hp)
Static thrust: 102 kgf / 225 lbf
Mounting: Single or twin
Steering angle: Up to 140°
Voltage: 48V DC
First published in the January 2022 issue of MBY.
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