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Thread: Advise needed on Electric Motors

  1. #1
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    Default Advise needed on Electric Motors

    I plan to replace an Atomic 4 in a Cape Cod Shipbuilding Marlin with a D&D ES-15-6 motor running at 48v. I have the motor but don't know whether I need gear reduction unit or not. Also I need to choose the optimum controller, contactors, and throttle. Iím a woodworker, boat rebuilder, and math major, but definitely not an EE, and frankly am sort of perplexed with the flow of electrons (that can kill you in an instant!) and torque.

    The ES-15-6 motor specs are:
    1. 48-72 VDC Series Motor
    2. 9 HP @ 72V Continuous Rated
    3. 65 Ft /Lbs Torque Peak
    4. 30 HP Peak with 450 Amp Controller


    Anyone out there who can help me???

  2. #2
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    Default Re: Advise needed on Electric Motors

    The electric drive isn't popular here among some of the members and you will probably get heavily flamed for thinking this is a good idea, sorry.
    I don't know anything about the boat you are intending to install this setup in sorry, so can't comment.
    The supplier of the motor would be the best source of installation information. If not, go to another supplier.
    My gut instinct is that you wouldn't need a reduction box if the max speed isn't crazy fast. You don't mention it in the specs.
    Getting the propeller size and pitch matched to the revs and HP curve, to get the hull to max displacement speed is the key.

  3. #3
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    Default Re: Advise needed on Electric Motors

    I don't see any graphs done at 48V for that motor, but I didn't spend a lot of time looking. What I saw was based on 72V only with peak HP at around 2,000 RPM and the continuous power rating at around 500 RPM. I doubt the 48V RPM will be much lower.

    regards,
    Joe
    These days, everything I do is just "puttering around"

  4. #4
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    Default Re: Advise needed on Electric Motors

    Thanks for your reply. I am interested and intrigued why wooden boat folks are down on electric drives.

  5. #5
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    Default Re: Advise needed on Electric Motors

    Thanks Joe. I'm embarrassed to admit that I don't know what the implications are of what you wrote on whether I need a reduction gear.

  6. #6
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    Default Re: Advise needed on Electric Motors

    BTW the boat I mentioned is a Herreshoff Fish class pulled out by Sidney Herreshoff for Cape Cod Shipbuilding to take a back stay. There were 300 or so built.

  7. #7
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    Default Re: Advise needed on Electric Motors

    Quote Originally Posted by j2us View Post
    Thanks for your reply. I am interested and intrigued why wooden boat folks are down on electric drives.
    I priced a system for my 22’ boat and it was going to be something like 50% to 70% dearer than a diesel and it has questionable range and a long recharge time. Let alone the weight and stowage room for batteries.
    You could probably add 20% for Banana Republic dues and I could have gone Lithium batteries but then the price went through the roof.
    Only advantages I can see are instant power and quietness. The green factor is debateable by the time you consider the manufacturing costs and the power has to come from somewhere. So that makes it even with diesel except for price and range.
    Thats why I’m down on it.

  8. #8
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    Default Re: Advise needed on Electric Motors

    Thanks for your reply. I am interested and intrigued why wooden boat folks are down on electric drives.
    I don't think people are down on electric motors. What comes up is that the electric ends up costing a lot more--and takes up more space in the boat--more often than not. At that point, the discussions become debates on value propositions and / or a cost-benefit analysis.

    Kevin

    Edit: Crossposted --sorry.
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  9. #9
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    Default Re: Advise needed on Electric Motors

    There are a couple of folks on this forum who have built electric-powered boats, and may drop in on this thread to offer their advice.
    If your Universal A-4 is in working condition, and you do the conversion, there are folks still running and rebuilding that engine, so
    you may be able to defray a bit of the project cost.

    Rick

  10. #10
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    Default Re: Advise needed on Electric Motors

    I think the issue most of us have with electric power is power density. At this point in a smaller boat for running in and out of a marina they work and are a viable alternative to a small outboard.
    But if you need to drive a 5 or 10 ton boat into waves and a head wind for a couple of hours let alone 8 hours motor sailing to windward then electric drive does not work.
    Also some of the sales literature dose not help when the promotors of electric drives say a 10 HP petrol can be replaced by a 6-7 HP electric drive due to the constant torque of the electric engine. Sorry but that's what gearing is for 10 HP at the prop beats 6-7. In either case you need to optimise your prop to suit your application.
    Zane

  11. #11
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    Default Re: Advise needed on Electric Motors

    I plan to make this boat into a daysailer/overnighter for use in the Chesapeake, so I don't need the power to drive a big yawl off a lee shore in a 30 knots breeze. Been there, done that. Just want to get home when the breeze dies at sunset and the lady or into a marina dock for a cocktail when I want to. I'm old now - I'll leave the offshore stuff to others' boats.

  12. #12
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    Default Re: Advise needed on Electric Motors

    Quote Originally Posted by slowpoke View Post
    I don't see any graphs done at 48V for that motor, but I didn't spend a lot of time looking. What I saw was based on 72V only with peak HP at around 2,000 RPM and the continuous power rating at around 500 RPM. I doubt the 48V RPM will be much lower.

    regards,
    Joe
    Joe, Can you tell me a bit more about whether I would need gear reduction for my 3000 lb easily driven boat. Thanks! - Jim

  13. #13
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    Default Re: Advise needed on Electric Motors

    Several centuries ago in college I had a course on DC machinery. I do remember that you should never plug in a series wound motor without a mechanical load. If you do it will spin up until it flies apart. You will have a load if it is coupled to a prop in the water. Just don't do it on the bench. Shunt wound motors are different.

    Having said all that, your 21st century controller may have circuitry that will limit the speed. Find out.

  14. #14
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    Default Re: Advise needed on Electric Motors

    As you can see J2, you may not get a good answer here. I believe there is an electric boat forum. You might also ask the Facebook WBF group, you can reach more faces that way.
    There's the plan, then there's what actually happens.

    Ben Sebens, RN

    15' Welsford Navigator Inconceivable
    16' W. Simmons Mattinicus double ender ​Matty

  15. #15
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    Default Re: Advise needed on Electric Motors

    Electric sounds like a good choice for your application if it interests you.

    People also sail with no motor, don't tell that to the diesel crowd.

    To answer your question about gear reduction, that all depends on the propeller. Play with sizing your propeller to various gear ratios including 1:1, you can probably get away with no gearbox.

    Here is one calculator. You will need to know RPM, power, and boat specs for your 48V setting.

    https://www.vicprop.com/displacement_size.php

  16. #16
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    Default Re: Advise needed on Electric Motors

    I'd be interested in knowing why the OP has decided to replace his Anemic 4 with an electric motor. Like many, I'm sure, the possibility of electric motors as a motive power in small craft has fascinated me. And, like most, after a very interesting study of the concept, I've discarded it as an option for anything other than easily driven displacement hulls used for limited periods of time on flat water. I came to this conclusion after speaking with a very knowledgeable marine engineer who was considered an authority... and a proponent... of electric auxiliaries who confirmed my suspicions. His lament was that after he'd had some widely published success in installing an electric auxiliary in a somewhat famous and very easily driven sailboat, some manufacturers jumped onto the bandwagon and began making wild claims about their electric motors. His comment to me was that the electric auxiliary that had gotten so much good press was never intended for anything other than limited maneuvering in and out of the marina slip and never intended for use as primary propulsion for the larger-sized racing day sailer into which it had been installed. He confirmed that it had very limited range and wouldn't serve for primary power in any kind of current or chop.

    I'm not "flaming" the technology and I wish it were viable, but the research simply doesn't support that conclusion. An electric motor doesn't produce the power to drive a vessel without a battery bank that takes up a lot of space and weighs a lot. Weight can be minimized somewhat with high-tech batteries, but at a cost that cannot be justified. Moreover, there is charging time and battery maintenance to consider. There doesn't seem to be any economy of scale, either. The bigger the boat, the more batteries it needs to run a motor appropriate to the job. In terms of comparable range, I've seen the automotive "bean counters" report that about 700 pounds of state of the art batteries will yield about the same motive energy as a gallon or gallon and a half of gasoline at 30 mpg. "Hybird" technology is an option, but only theoretically. Diesel-electric propulsion has long been an excellent motive option, as demonstrated in trains and tugboats and other applications, but for small pleasure craft, if you are going to run an internal combustion engine to power a generator to run a motor... well, you might just as well stick with an internal combustion primary engine.

    There are still a lot of Atomic 4's out there, Some years back, Westerbeke was still offering parts, but at a price. Some of the major components are no longer available except as salvage. These include the block and oil pan and the mechanical fuel pump. As they become less numerous and as the NOS parts supply dwindles, parts will become more expensive. In the long term, from what I've been hearing in recent times, many Atomic 4 owners have decided that the relatively small additional cost of installing a comparable small diesel (e.g. Yanmar, etc..) as against a rebuild on their Atomic 4, is justified by the diesel's greater range and reliability and the fact that the engine will be new.

    When I was in high school, I had a geometry teacher that announced on the first day of class that he would give an "A" to any student who by the end of the year figured out how to construct a square that had the same plane surface area of a circle using just a compass and straight edge. I was immediately intrigued by the challenge and spent the better part of the year trying to accomplish just that until I came to realize, from the theory I was learning along the way, that "squaring a circle" is impossible with a compass and straight edge. (This led me in later life to an interest in planimeters!) It wasn't a fruitless exercise, because I did earn an "A" in that class, primarily because that initial challenge had kept my attention throughout the course. (Smart teacher!) I think designing an efficient and workable electric auxiliary motor is probably a lot like squaring circles or designing perpetual motion machines. Intuitively, it seems like it ought to work well, but the devil is in the details.

  17. #17
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    Default Re: Advise needed on Electric Motors

    π is transcendentally irrational.

  18. #18
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    Default Re: Advise needed on Electric Motors

    I had a quick look for the motor you mentioned online and it appears in lots of catalogues with not a lot of supporting documentation.
    The advice to try to find an electric boat forum is good.

    The normalisation of full electric road vehicles means that the technology is gaining volume efficiency for cost.
    There are electric hybrid launches on the market now in Europe that give acceptable performance compared to diesel only versions of the same boat (at lower top speeds)., so this is totally doable for your proposed use.

    Most of the conversions that I have read about involve an experienced supplier that has managed the specification and installation.
    An electrical engineer would be able to sort themselves out, but going DIY after picking a motor out of a catalogue may end up more expensive than paying for the experienced suppliers time.

  19. #19
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    Default Re: Advise needed on Electric Motors

    I guess the rational behind electric leisure-boat is not very different from the rationals behind electric cars (Tesla etc....) :
    - If you stick to very classic electrical technologies (continuous current motors, lead batteries etc...), your specs will be substantially below current mainstream gas or diesel solutions but you can get satisfactory results if you address some particular needs that don't need very high specs ("classic" electric vehicle have been practical & cost effective for a long time in factories & hospitals). You must understand that even for continuous motors & lead batteries the questions of controllers and battery chargers are not trivial and you need either quite good engineering knowledges in that domain, or reputable commercial offerings really adapted to your needs.
    - If you chose more advanced electrical technologies (brushless motors, lithium batteries etc...) you can get specs not far from low end diesel motor's specs, but motor + battery + ... costs will be at least 3 times equivalent diesel provided you find a suitable fully integrated industrial product (the whole chain...). This cost might be economically justified in some cases because of gas-saving or because of zero-pollution restrictions in some places, but more often it is not (a bit like Tesla cars...). I guess main advantage of electric boat vs electric cars is that a 9hp electric boat should cost only a fractions of Tesla cars costs.

  20. #20
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    Default Re: Advise needed on Electric Motors

    Several years ago a woman posted here who bought a small classic cruiser, had engine trouble on maiden voyage on the Chesapeake and was convinced to install electric power. There was quite a bit of opposition here to her idea. She did the expensive installation and was not heard from again. Probably that tells the tale right there.

  21. #21
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    Default Re: Advise needed on Electric Motors

    A compound motor would be even better, providing the benefits of both the high torque series as well as the controllable shunt windings. These don't have the destructive nature of the series only motor.

  22. #22
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    Default Re: Advise needed on Electric Motors

    Quote Originally Posted by j2us View Post
    Joe, Can you tell me a bit more about whether I would need gear reduction for my 3000 lb easily driven boat. Thanks! - Jim
    No, I can't.

    The electric motor operates at lower RPM than the Atomic 4, so if you had the 18HP Atomic 4 with the 2:1 reduction gear, then I surmise that the electric motor, without reduction gears, would perform similarly to the Atomic 4 when it was operated at less than 1/2 throttle. That electric motor at 48V will not match the Atomic 4's capability above 1/2 throttle, no matter how you gear it or change the propeller.

    If your Atomic 4 used direct drive or was the 30HP motor, then the difference is too great for me to address.

    regards,
    Joe
    Last edited by slowpoke; 10-22-2017 at 08:35 PM.
    These days, everything I do is just "puttering around"

  23. #23
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    Default Re: Advise needed on Electric Motors

    Hi
    I recently rejoined the forum after a long time away (different name though)... but I have now used electric inboard in my sailboat for more than 10 years. Second battery set going...
    short reasoning why: silent, actually more efficient than old diesel was (diesel max 4.5 knots, electric 5.1 knots), price difference to new diesel was not large...
    last year I installed larger solar panels so now I can charge the batteries even when there’s no shore power nearby...
    batteries are now two 12 volt AGMs in series so I get 24 volts to motor for 4.4 kW. Works for me, as usual YMMV.

    And I get to sail more as the batteries won’t go as far as a tankfull of diesel would have...

  24. #24
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    Default Re: Advise needed on Electric Motors

    I didn't find complete specs of the D&D ES-15-6 motor, but I understand it is a brush-type serially wound DC motor (which might probably also be used as an AC universal motor...). Most of those motors have high power to weight ratio but torque is low at low rpm, which means that you need to get to relatively high rpm to get some power. They are similar to vacuum-cleaner or hand-drill motors : cheap and powerful but rather low-tech with some limitations.
    For boat propulsion I guess you won't be able to get reasonable power out of this motor & reasonable propeller efficiency if you don't use a reduction gear. For calculus you should start with propeller diameter (correct diameter for the intended power, might be limited by boat shape...), then propeller pitch & rpm for max efficiency at intended cruise speed & power, and last motor size & reduction ratio. Motor size should be large enough to get needed torque & power at cruise level with continuous use qualification. This should enable to calculate controller min size : large enough to give cruise level voltage + 20% and cruise-level amperage + 20% with continuous use.

    For 9hp continuous power, it might be cheaper to buy a slower running motor you can connect directly to prop shaft rather than a motor + reduction gear + thrust bearing. You can find slow-rotating motors (max power at 300 or 1.500 rpm...) with reinforced bearings you can connect directly to prop shaft without additional thrust bearing. It will be more expensive than the D&D ES-15-6 motor but extra cost might be less than reduction gear + shaft front bearing. Also, it might be worthwhile to buy a brush-type permanent magnet DC motor rather than a brush-type serial-wound DC motor, because torque curves of serial-wound DC motors might give you serious integration headaches.

    According to what I understand from your needs, I would look for a ready to install kit for boat propulsion, including a 9hp direct-drive brush-type permanent-magnet DC motor and matching controller & battery management system for lead batteries. I have seen such systems on Internet but price tags seem a bit excessive (7k$+).

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