Yamaha’s new propulsion system

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

  1. SolGato
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    SolGato Senior Member

    By design, this system should be more efficient moving a vessel at lower RPM due to it being a pull rather than push prop and with it not having a large mass in front of the prop to disrupt flow. So in theory, the rim drive should provide thrust more efficiently over a conventional E drive. The Kort nozzle should also help in overall efficiency while improving steering and maneuverability.

    When it comes to thrust versus power input, electric boat motors generally speaking are least efficient at lower RPM as they try to push a vessel through the water, so any improvements you can make at low RPM will be beneficial, especially if you are trying to swing a larger prop which can make things even worse by overloading the controller. For example, my brushless motors are about 55% efficient at lower throttle compared to 80% at mid and 70% at high.

    What I would like to know about HARMO is if the motor is PWM, and if so what the max efficiency is (watts in versus watts out) while PWM is working, and at what RPM this occurs. Typically this would be at around 70% throttle.

    This information would tell you what your max cruise speed consumption would be which would then help to determine how much battery capacity one might need for their typical use, and or the size solar system needed to offset that consumption so that a vessel could be run on sun only.

    Right now I am able to cruise at 5MPH mid-day without pulling from my battery bank.

    Increasing system voltage is one way to improve efficiency, but often requires a larger solar system and more complex battery bank. But generally speaking, a 24V motor will consume 2X the amps of a 48V, so there is a big advantage to a higher voltage motor in relation to battery capacity and range. Doubling the voltage basically doubles the capacity of your gas tank. I’m glad Yamaha settled on a 48V architecture. Anything more and things start to get dangerous and more complicated with respect to batteries and charge controllers. With 24V LiFePO4 batteries being more readily available these days, a pair of batteries in Series or a purpose built marine propulsion battery would be all that most users would need to keep things safe, simple and manageable.
     
    Last edited: Sep 18, 2021
  2. alan craig
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    alan craig Senior Member

    Quote: 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.

    This seems to imply that a gearbox on an I.C. engine is acceptable but a gearbox on an electric motor is not.

    Outrunner/rim drive motors nominally have higher torque than smaller dia. motors but they can be, and are, available with different kV(speed per volt). With a lower kV a motor will have higher torque.
    My little electric outboard (thread about boat data in this forum) can turn through 360 degrees - or it could if it wasn't steered by a push/pull tiller.
    Pod drives would fit under that transom shown and leave the bathing area completely unobstructed and give the same manouvrability although it could not be raised above the waterline.
    Ducts add their own parasitic drag - but the cooling of the rim drive should be excellent.
    The wake is a function of the boat's resistance, not the power system.
    EDIT: I'm not saying that there is anything particularly wrong with this system, but I don't think it has any real advantage.
     
  3. alan craig
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    alan craig Senior Member

    ... and another thing - all brushless motors are "PWM", they are pulse width modulated for power level to all three phases, with the timing of each delivery of power to a phase being controlled by feedback from sensors or from the back emf.
     
  4. SolGato
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    SolGato Senior Member

    Yes, a gearbox is not desirable in an electric boat motor design if low noise and efficiency are important to you, yet are acceptable in an ICE motor.

    Your motor could turn IF…..

    POD drives would fit under the transom shown ALTHOUGH….

    Not having to tend to a tiller and being able to turn 150deg are “Real Advantages” to some of us, just like being able to tilt a motor out of the water for beaching, shallow water navigation, and to keep growth off of it.

    It sounds like the features of HARMO aren’t for you and that’s fine, but that doesn’t mean that it isn’t a good fit for others who see and appreciate the benefits and advantages over other systems.

    I’m glad to see more offerings and different takes on electric propulsion, and for me HARMO checks a lot of boxes and offers a number of important advantages over comparable sized electric propulsion systems.

    In fact another advantage I would add to my list is that the motor system is less likely to be stolen, which is a real problem with popular electric outboard designs. I’ve seen quite a few Torqeedos for sale second hand on Ebay listed by pawnshops that are missing things like batteries, chargers, etc.. Outboard motor theft is so bad in some US states, they actually issue Titles for them as proof of ownership.
     
  5. SolGato
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    SolGato Senior Member

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  6. gonzo
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    gonzo Senior Member

    The power loss of a properly designed gear box is less than 3%. What makes the loss acceptable on an ICE but not in an electric motor?
    Also, if the gearbox is noisy there is a mechanical problem.
     
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  7. SolGato
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    SolGato Senior Member

    Please provide documentation from the ICE manufactures that shows they have designed their gearboxes for less than 3% efficiency.

    Every percentage of efficiency is/should be important to electric propulsion users unless they don’t understand the importance, whereas the majority of ICE users could care less.

    How many buyers of ICE outboards shop based on what the sticker says it gets MPG?

    They buy based on HP. Overall inefficiencies are acceptable to them. And the majority don’t even keep their motors in good running condition.

    So you’re saying a gearbox that makes noise has a mechanical problem?

    That 2 gears in bevel configuration spinning at thousands of RPM’s are silent?

    Do you think my brushless direct drive motors are as loud as the lower end of an outboard?

    Do you think Torqeedo introduced their new direct drive motor touting how quiet it is over their other gear driven motors providing dB specs and all just because they were bored and needed something to do and market?

    Gears are noisy. Gears are less efficient. And efficiency matters when you are powered by the sun and or limited in battery capacity.
     
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  8. gonzo
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    gonzo Senior Member

    Modern gearboxes have less than 3% power loss. It is a well known value. https://www.researchgate.net/publication/331507104_POWER_LOSSES_OF_GEAR_SYSTEMS

    Efficiency is important to all users, including owners of ICE engines. Buying an engine based on HP is proper engineering since they will provide the power necessary for proper operation. It is the same as people buying electric motors. Please provide documentation of why you claim they don't.

    Your claim that the majority of ICE engines don't keep their equipment in proper running order is simple nonsense. You are inventing stories to puff up your opinion.

    Modern gearboxes are very quiet. Some electric motors are noisy. It depends. However, noise and vibration are an indication of bad design or a mechanical problem. Electric motors are a mechanical contraption too.
    In short, do you have any proof to back up your claims?
     
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  9. SolGato
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    SolGato Senior Member

    Blah Blah Blah…. your track record for condescendingly challenging people, taking the things they say out of context, poking holes in their statements, and providing general figures, values, and specifications is well documented on this forum.

    I responded to your post just as you typically do, knit picking the general statements you made about gearbox efficiency and noise, and I’m not at all surprised by your response. Classic Gonzo.

    I’m here to help people if asked, ask for help and opinions when needed, and share what I’ve learned from real world experience and application.

    I don’t make things up or typically contribute unless I have first hand experience, unless the discussion is about exploring a new idea or concept.

    I’ve been around this stuff all my life, a member of many forums, and there are always a few like you that like to argue about things for the sake of argument.

    I don’t need to prove anything, you don’t need to believe me, and honestly I could care less what you think.

    Thanks for your response, it confirmed what I had already suspected based on your interactions with others.
     
  10. srimes
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    srimes Senior Member

    What the heck is a "pull" vs. a "push" prop, and how much difference does that make?
     
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  11. SolGato
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    SolGato Senior Member

    If I remember correctly, the significant efficiency advantages Yamaha makes claim to is also in part due to it being a rim drive design.

    So not only is it pulling, but because there isn’t a big motor in front of the prop like trolling motors or other electric outboard designs, there isn’t anything disrupting the flow of water in front of the propeller.

    I think mainly what Yamaha is claiming with respect to the way they are marketing this system and the purpose for which it was designed, is that it has a significant advantage in slow speed maneuverability of a vessel, as well as an overall improvement in efficiency.

    At low RPM electric boat motors are somewhat inefficient compared to cruising speeds. So if you’re doing a lot of slow speed maneuvering, any improvement here is a benefit. Since this system was designed for busy waterways, slow speed efficiency and maneuverability gains may make it appealing if say you are operating a water taxi in Venice.

    A general comparison to other 48V 9.9hp equivalent electric boat motor offerings seems to back up Yamaha’s claims. True performance on an actual boat would bring other variables into play, but it is interesting to see how they compare on paper:

    Yamaha Harmo: 225lbs thrust @ 3.7kw
    Elco EP20: 195lbs thrust @ 4.7kw
    EPropulsion Navy: 6.0 280lbs thrust @ 6kW
    Torqeedo Cruise 4.0 (8HP equivilant): 189lbs thrust @ 4kw

    From what I’ve read, at this point in time Yamaha’s system will only be available to production builders, so I imagine they will be the first to have access to more specifications.
     

  12. gonzo
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    gonzo Senior Member

    I do poke holes on unsubstantiated statements. In general, people like you resort to personal attacks instead of showing that any of my statements are wrong. You seem pretty riled up, which belies your claim to not care less about what I think.
     
    SolGato likes this.
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