Planing Electric Dinghy

Discussion in 'Boat Design' started by feunatz, Nov 13, 2016.

  1. feunatz
    Joined: Nov 2016
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    feunatz Junior Member

    You are absolutely right. I'm not aiming to create something practical with real range and daily usability - If i could I'd sell the concept and never work another day in my life ;)

    Indeed Weight and economy of scale is the enemy. Real usable electric/hybrid boats exist in the 10ton+ range, where 2000kg batterypacks don't ruin the boats performance.

    Some of my calculations:

    i took the Flying Saucer 190lbs hull for this example:

    Electric only:
    hull: 84Kg
    Motor,Controller,Wiring,Driveshaft: 14Kg
    Batterypack: 12Kg
    Misc Stuff(Vests,Oars,Beer): 10Kg
    Driver: 80Kg

    Total: 200Kg

    Electric + 2KW Generator + Charger:
    Electric: 200Kg
    Generator: 24Kg

    Total: 224Kg

    6HP 4-Stroke:
    Hull: 84Kg
    Driver: 80Kg
    Outboard: 25Kg
    Fuel: 10Kg

    Total: 209Kg

    Drive Performance:
    If I'm not mistaken current outboard Horsepower is rated at the prop? so an 6HP will at some point deliver 6HP to the Prop.

    My planed Drivetrain Specs for Electric:
    PMSM 25KW(peak!) Motor
    90V 800A Controller
    Custom 2KWh 72V Battery Pack

    Prop Power output and runtime estimations factoring 80% Drivetrain Efficiency
    16,3KW(22hp) for 4minutes
    10,8KW(15hp) for 9minutes
    2,7KW(3,7hp) for 32minutes


    All calculations are done with measured Cell/Battery Data(not claimed specs). Thats why going from 10 to 16KW cuts the runtime in half as the pack aproaches its limit. But to be hones i have no idea if my speced motor can even survive 16KW for 4minutes.

    For the heavy configuration with the 2KW Generator ther is a gain of 1-1.2KW in output Power. 1KW gain will not upset the 24Kg wight penalty but ads a little cruisability.

    So Going for Max Range with the generator running 3,7KW for roughly 30minutes. Keep the Generator running and 75minutes(or a swim and two cold ones) later its ready for another run.

    This is not an ideal configuration, but one that fits my budget.
    Better would be add 3more Batterypacks(using Highcap vs Highdrain cells) for a total of 9,5KWh of energy storage and run with generator and 4-5KW output for over 90Minutes.
     
  2. feunatz
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    feunatz Junior Member

    Maybe a interesting sidenote on torque:

    Yamaha DF6: 17Nm/13ftlbs@5000rpm to the prop
    Electric Motor(16KW): 44Nm/32ftlbs@0rpm to the prop

    ...roughly the same as a Yamaha F20B@5500rpm
     
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    The minimum power suggested was 15 hp. You really want something close to flat bottomed, super light (any thing you can save in hull weight can go into batteries). Your endurance at planing speed is the big problem, as mentioned by others. But you could potter around for hours at sedate speeds, if you select a hull designed for that. Even a planing hull is going to go a lot further at a slow speed, before you flatten the batteries.
     
  4. mydauphin
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    mydauphin Senior Member

    Reality sucks... electric boats are not very fast for very long.
     
  5. feunatz
    Joined: Nov 2016
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    feunatz Junior Member

    So all my hull suggestions were pretty much as wrong as they could be. Thanks for bringing me somewhat closer to reality.

    But I'm just not ready to throw style completely overboard. At least give it a last try.

    What about the Bateau RB12
    http://bateau.com/studyplans/RB12_study.php?prod=RB12

    Estimate has it at 60Kg(24Kg lighter than the Flying Saucer.) Low deadrise but not flat(Maybe i could change that for the aft section). I'm Pretty sure i could also shave another 10Kg off, even make the deck only decorative if needed.

    EDIT:
    "Built light and with one person on board, she will plane with a 10 HP but will feel better with a 25." - looks like i would have to build i VERY light.
     
  6. Irie
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    Irie Junior Member

    Sure seems like you've put some thought into it. Where are you planning to put the prop? Under the hull or behind it?
     
  7. feunatz
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    feunatz Junior Member

    I'd like to have prop and rudder both under the hull to keep the back clean.
    Any pointers on prop angle? As low as possible?
     
  8. mydauphin
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    mydauphin Senior Member

    The minute you start design boats, props and rudders you start running into compromises. Putting under hull means more draft. The work better there but now your talking shaft, seals, angles and problems trailering, beaching. I would go with tiltable outboard.
     
  9. Irie
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    Irie Junior Member

    An outboard conversion would definitely be the path of least resistance, and with the higher rpm of your motor performance should be better than what I saw when I did mine. It might also be more efficient, but you don't need the gear reduction and may find that doesn't use all your motors potential. I have controller data from my outboard conversion, my drive at 20°, and my drive in surface piercing mode if that info would help you I can make it available.

    I really like having the ability to control how much of the prop is in the water as it allows me to adjust the load on the motor to some extent. A quick example is at 20° with a 9.25x10 prop I can run 12 mph at 200 amps which is my motors continuous duty rating. If I trim up and run the prop on the surface I can run 16 mph @ 215 amps. I'm sure this comes as no surprise to those familiar with surface drives but its rather neat to see it in the controller log. I don't have enough experience to offer advice, I can just share what my setup does and maybe that helps you with your decisions
     
  10. mydauphin
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    mydauphin Senior Member

    I agree but after 40 years of boating, these are my conclusion. Small boats should be outboards. Large boats should be diesel. It is ok to have one engine, but have three batteries, and two fuel tanks. Batteries and solar are good for house systems. Not developed enough for traveling beyond your sight or paddling abilities. 90% of the time you are traveling at hull speed. Planning boats are great for getting you somewhere quickly as long as you have enough fuel get back. They always consume more than you figure. So be careful with the throttle. Carry a rope to be towed, and an anchor in case no one will help you.

    Sorry if I give to much advice, been out in the sun too long.
     
  11. alan craig
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    alan craig Junior Member

    Feunatz, the picture in your post 7 looks ideal for electric (low power) planing - flat bottom, no rocker. But a converted sailing catamaran would steer much better with differential power. It would depend on which hull was available.

    That Neu motor looks awesome and small enough to adapt to an outboard, an outboard being the only positive suggestion from Mydauphin, which I second. Here is my electric outboard using a kv130 brushless motor; only used at 800w but capable of about 3Kw:

    I used a 3hp Evinrude as the basis for my conversion; you would need something a bit bigger obviously.

    Also, have a look for the Wye Island Electric Boat Race for some examples of of boats with about 30 mile range at up to 12 knots.
     

    Attached Files:

    Last edited: Nov 21, 2016
  12. sailhand
    Joined: Jan 2017
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    sailhand Junior Member

    I have a design that is perfect for low power electric conversion in fact I have been talking with torqeedo about just that. Check out magic carpet 3.5 catamaran on youtube

    https://www.youtube.com/watch?v=SA6cDk2Imb0
     
  13. BertKu
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    BertKu Senior Member

    I have my engine as an outboard motor but my motor compartment is at the same time my rudder. You should consider my set up whereby I run my brushless out-runner motor in transformer oil already for 4 years. The transformer oil gets via the aluminium/steel casing cooled by the water . I have never measured any efficiency drop because of that. I am happy. The internal temperature does not increase more than 35 degrees. But I run only this at 1 kw at 24 volt. Just something controversial.
    The Finish company Oceanvolt claims that their 15 kw motor is equivalent to a 45 pk diesel motor. (www.oceanvolt) while Torquido claims a 3.7 kw Torquido motor equals a 8 hp engine. I have my own opinion and yes the torque of my brushless motor is massive in view that the internal resistance at 1 RPM is very low and therefore the split second high current is massive when the controller is slightly opened. We talking about 200 - 300 ampere at 24 volt. Maybe that is by them confused with propshaft output.
    But both make beautifull products. Bert
    P.s. the motor with wires and sensors are all submerged in the oil. One can only use transformer oil , in view that it is high insulation for electrics submersible.
     
    Last edited: Apr 2, 2017
  14. JosephT
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    JosephT Senior Member

    A stern mounted motor is definitely the way to go for lighter boats. If you're set on electric I would suggest taking a good look at Minn Kota trolling motors. They are very reliable and run nearly all day on a charged up marine deep cycle battery. They have great endurance and can run almost all day (built in digital "Maximizer" technology). I have a 55lb thrust trolling motor on one of my boats and it runs great...good torque. For choppy/windy harbors I would probably go with an 80 or 112lb thrust.

    No sense on reinventing a wheel that has already been invented...for a good price too. Various thrust levels available. Options for hand or foot pedal control.

    http://mk.factoryoutletstore.com/cat/21038/Minn-Kota-Riptide-Series-Trolling-Motors.html
     

  15. BertKu
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Feunatz, I don't know whether you are a hobbyist. If so, I wonder whether the controllers I have been making also would work in transformer oil, without consequences. I will experiment with them in oil. There are no potentio-meters nor variable resistors and in principle it should. You are considering > 6 KW motors and the golden rule is approx 10% will be converted in heat. 600 watt+ is a lot of heat to get rid off plus the heat what the controller generates. In your design you could consider that route to go. The problem is that water cooled brush-less motors are quite costly, while normal brush-less out or in runners are affordable and easy available. Bert

    p.s. You considered in your #1 thread 2 x 16 kw, that is a lot of heat generated. 3200 watt + another 600 watt for the controller to cool. Well one advantage, in the winter it will help you to stay warm. I personally think that 2 x 16 Kw is too much. If we can trust the OceanVolt statement 2 x 45 Hp diesels for a small planing boat is equivalent to 2 x 16 KW brush-less motors, I think you can scale it down to about 2 x 6 KW.
     
    Last edited: Apr 6, 2017
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