Yamaha’s new propulsion system

Discussion in 'Electric Propulsion' started by SolGato, Sep 16, 2021.

  1. SolGato
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    SolGato Senior Member

    Yamaha has a new electric propulsion system HARMO based on rim drive technology that offers a lot of features missing from the current electric outboard offerings, those mainly being built in electric trim/tilt and steering with control via a joystick.

    Built and installed like an outdrive, it works more like a bow thruster pulling the vessel through the water rather than pushing, and offers excellent maneuverability and low noise operation.

    I predict we’ll see more manufacturers integrating this drive system into their designs as it looks slick and based on its weight, is likely built to last.

    I can’t find pricing anywhere yet, but the are starting to take pre-orders.

    Basic specs are 225ftlbs thrust / 3.7kW /48V / 121lbs weigh and is stated to be equivalent to a 9.9HP.

     
    Last edited: Sep 16, 2021
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  2. duluthboats
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    duluthboats Senior Dreamer

    Cool. What is it, 3.7kw or 9.9hp? It would look great on my current project. I will wait and see what the coast is.
     
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  3. SolGato
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    SolGato Senior Member

    When it comes to marketing electric motors, they are often stated as being equivalent to a certain size ICE motor. What they are referring to is propulsive thrust not horsepower, that is to say the electric motor will move a particular boat as well as the equivalent ICE, but it does not necessarily mean it will achieve the same speeds. A lot of electric motors are limited in RPM or prop size due to being direct drive, whereas an ICE outboard for example uses a gear reduction that allows the prop to spin faster or a larger prop slower. Some electric motor manufacturers incorporate a gear reduction which allows them to spin a larger diameter higher pitched prop giving higher speeds, but this makes the motors less efficient and drastically reduces range. Anyway, until we know what the max RPM is of HARMO and what the propellor specs are, it hard to know how comparable it might be to a 9.9HP with regard to high speed. And the 3.7kW spec could be consumptive power, or output power.

    I’m hoping since Yamaha is a traditional ICE motor manufacturer that when they say it is equivalent to a 9.9hp, it is a truly comparable and able to push a vessel to the same top speeds, and that they aren’t using the same confusing vocabulary that the electric motor manufacturers have been using for years. A lot of people have been duped not understanding the way the two are compared. The rim drive design certainly lends itself well to some sort of gear reduction and the ability to spin a large propellor without a big disruption in flow like a brushless direct drive motor,

    Hopefully more info will be available in the months to come that will give us a better idea of HARMO’s performance.
     
    Last edited: Sep 16, 2021
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  4. fallguy
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    fallguy Senior Member

    Very cool. Would love to see specs.
     
  5. Heimfried
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    Heimfried Senior Member

  6. fallguy
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    fallguy Senior Member

    Looks like the start of smething good. But 9.9hp ain't gonna get many buyers excited.
     
  7. Heimfried
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    Heimfried Senior Member

    A fraction of boaters (not a tiny one) will find it too weak and are like "no stern wave no fun". These people are shurely not the customers of HARMO.
    But if you look at it in a sensible way you will find that stern wave ist a sign of wasted energy.
     
  8. Heimfried
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    Heimfried Senior Member

    This is basically a kind of electric drive which I will try to build myself in the next years. (I'm building a 6 meter ply on frame solar electric power kat with deckshouse for inland use on small rivers, canals and lakes, started 2017. Since then I collect construction ideas about effective electric propulsion.)
     
  9. powerabout
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    powerabout Senior Member

    Rim drive but it has a hub, sort of adds drag and complication that the rim drive avoided?
     
  10. Heimfried
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    Heimfried Senior Member

    A Rim drive as I understand it, is defined only by power transmission to the circumference of the rotating object (kind of wheel) in contrast to power transmission along a shaft and a hub. There were several attempts to establish Rim drive as a propulsion in the recreational boat sector (starting in the 1990er?) mostly associated with an hubless propeller which would have a lot of pros - in theory. As it seems the hub is - at least for the time being - necessary to ensure the precise rotation and has to be accepted for now.
     
  11. alan craig
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    alan craig Senior Member

    Well it is definitely rim drive - coils in duct, magnets in propeller rim - but it has a centre bearing. I can't see any advantage over a conventional outdrive.
     
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  12. fallguy
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    fallguy Senior Member

    turning 90 degrees is a pretty big advantage
     
  13. Heimfried
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    Heimfried Senior Member

    I respectfully disagree, Alan.
    I see a lot of advantages - in principle. If they play out is another question, but I think if YAMAHA is constructing/producing it, it will be more than hot air.

    - A Rim drive provides a much longer lever than a conventional outdrive so at low rpm a high torque.
    - Hydrodynamically is a prop with relative low rpm and relative large diameter substantially more efficient than a conventional outdrive.
    - The water stream out of the ducted prop is more focused than in a open prop arrangement so the steering effect is better.
    - As said above the (impressive to me) absence of a stern wake is a sure sign of a reduced energy waste.
     
  14. SolGato
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    SolGato Senior Member

    This propulsion system was designed for a specific market. If you need more power buy an ICE motor. This was designed for canals and waterways where noise, air and water disturbance are issues.

    There are a lot of advantages to the rim drive design and good reasons for why Yamaha chose to use a stern drive like architecture.

    If the motor had been designed like a conventional trolling motor with direct drive, it would cause a lot of water disruption. And if they had gone with a more traditional transom hung design, it would not allow it to be integrated into the popular small boat designs of today that incorporate a rear swim platform and unobstructed stern entrance/exit.

    I think they were quite smart to fill this niche, and 9.9hp at 48V is probably about right for what can be supported with respect to battery banks, solar, etc.. without the cost getting too disproportionate while still providing adequate cruising speed range.

    Lately I’ve seen a lot of people building solar electric boats with a big imbalance between the amount of power the motors consume versus how much power can be stored and harvested onboard. If you have ample power generation aboard a yacht or at the dock, then plugging in might be a good option for runabout/tender use. Otherwise designing with autonomy in mind is the best way to go.

    It will be interesting to see how it compares in cost to a 9.9hp ICE with trim/tilt and remote control. Yamaha is certainly in a better position than most to be able to manufacture and deliver a reasonably priced product. I don’t count the cost of batteries because that would be like factoring in the cost of gasoline and oil over X amount of hours of use, and I don’t count the cost of a solar system because that would be like owning the gas station.

    Here’s an example of a boat that was displayed at the Genoa boat show with a HARMO system:
    50BF4401-2518-4034-A3BE-68AB5B26B22F.jpeg
     
    Last edited: Sep 17, 2021

  15. powerabout
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    powerabout Senior Member

    I havnt seen any tests on thrust versus power input of conventional prop versus rim drive, anyone?
    On larger ones they have other advantages like swallowing large objects ( no hub) and allowing space saving etc.
     
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