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

    Planing Electric Runabout

    I'm just starting the process of building an new Electric(Gas-Electric) Dinghy.

    Drive System will most likely be 2x18KW Brushless motors. Direct drive @ about 5000rpm. I'd like to omit a rudder an use differential for steering.

    Now i need to find a matching hull

    Weights:
    Motors+Controllers+Steering Electronics: 40lbs
    Battery Pack(in Fireproof box): 35lbs
    2kw Generator: 46lbs

    Generator and Battery Pack can be positioned for best performance. Motors will have to be somewhere in the middle. Rather wide hull to get the props further apart would benefit the steering efficiency.

    A realistic sustained output power to the props would be around 16KW. Target Topseed would be around 25kn - realistic?

    Hull construction
    Preferably PLY stitch and glue(to heavy?)
    Balsa Core Glas/Carbon would be possible to
     
    Last edited: Nov 20, 2016
  2. Munter
    Joined: Jul 2007
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    Munter Amateur

    You are taking a lot on trying to make a hybrid drive train as well as integrating differential steering into this craft. I can't comment on the specific design parameters you have sought advice on but I can suggest that adding multiple layers of innovation can create incredible unnecessary complexity and multiple potential points of failure for the concept. I would include a rudder.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Why the twin props ? You just dropped a lot of mileage right there.
     
  4. Irie
    Joined: Jul 2016
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    Irie Junior Member

    What motor and battery pack are you considering? I've got 2 48v Chevy volt modules (43lbs each), a 10kW continuous 19kW peak pmdc brushed motor (30 lbs) in a 12' aluminum semi-v. Its a direct drive DIY steerable, trimable, surface drive. It'll push the boat 21 knots burning 13.7 kW. I have a thread about it here.
     
  5. feunatz
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    feunatz Junior Member

    I do not think my project has much innovation. Motors, Batteries and Controller are well proven and simple adaptations. Controlling the Thrust-mixing for steering is also pretty simple - Just some initial calibration needed.
    I'm more concerned about the "boating" stuff, since i have do admit my knowledge on hull design is next to nothing.

    Getting the Prop position and angle right. Angle will most likely be fixed so do i need a way to trim the boat(plates). Setting the center of gravity and so on....

    My idea was to loose some fabrication work, since making two identical propshafts vs shaft+rudder seemed like the easier way.
    Also i thought by elimination rudder drag and maybe using energy recovery on the trailing motor it could be more efficient.

    To energy recovery in general:
    I could go for max maneuverability by allowing the motors to run in reverse during steering or use Braking(Energy Recovery) on one Motor boosting overall power to the remaining motor. But there probably no way to know the better route before trails and that's an easy Software change anyway.

    I've seen your thread, great information there.

    Motor: the NeuMotors 8038 15KW cont. 30KW peak is my current pic(but some Paramotor-Motors also look very promising)
    Battery: Custom 18650 Pack around 14S14P - 2,4KWh total storage

    Battery Pack will be the limiting factor at 20-25KW and will be empty after 6 minutes at full load. Using the generator to recharge takes about 75minutes.
    Or i can go 4KW für 60min an then have tor slow to 2KW.
    I do realize the limited range is a huge drawback for most, but it fits my use case(lake) pretty good.
    "sprint and drift" like a good old russian sub*G*
     
    Last edited: Nov 14, 2016
  6. Jim Caldwell
    Joined: Aug 2013
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    Jim Caldwell Senior Member

    Be aware you are going to need very good AIR cooling to keep that outrunner alive even though it is an Neu Motor. I love them and have several all inrunners and watercooled.
    Email Steve Neu and discuss it with him, he very helpful.
     
  7. feunatz
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    feunatz Junior Member

    Thanks for the advice.
    Battery Pack also needs a lot of cooling. current plan is to force air cool the battery pack and pipe the waste air to the motors and vent from there to create a safe vent path for any components that can emit magic smoke. ;)

    Watercooled inrunner with water cooled controllers would be another possibility. As of now i was unable to find suitable inrunner at ~100-150kv

    Back to hull design, would a shape like this be beneficial or bad for planing(drag)?
     

    Attached Files:

  8. feunatz
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    feunatz Junior Member

    One of the first obstacles just presented itself - Finding suitable props.

    Rough guess for propeller need would be in the 6X9 range but finding a RH+LH of these seems to be rather difficult. Any pointers?
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    Seriously, you cannot depend on differential engine operation for effective steering control.
     
  10. feunatz
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    feunatz Junior Member

    I'm no expert on the matter and if the pros here tell me to drop it I will do so and continue on a more conventional route.

    But please help - I fail to understand why it won't work.
    At full Throttle and full steering input i have 2 possible configuration options.
    -Running one Motor at 120% forward and the other on max braking/regeneration
    -Running one Motor at 120% forward and the other 50% backwards

    And thats the worst case. speering performance will increase with lower overall power settings.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    You think your boat will still be planing with one engine "120% forward and the other 50% backwards" ? You are creating unnecessary problems, the idea of twin drives is not ideal, without a rudder you must like big problems. Good luck !
     
  12. feunatz
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    feunatz Junior Member

  13. feunatz
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    feunatz Junior Member

  14. mydauphin
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    mydauphin Senior Member

    Electric boat people give me a headache, mostly because they don't understand the power necessary to push a boat into the water, and the battery requirements to do this for more than a few minutes.

    First, you need to figure out the minimum hull speed that a hull will plan. The lowest I have even seen is about 14 knots. On a Jon Boat with one person, which is a flat bottom, light boat, the perfect combination, it takes about 5hp with one person. You need a hull that planes fast, deep vees, which are great, are not quickest to plane.

    So how many batteries do you need to power a 5hp electric motor for say 10 minutes at full power without it catching on fire?

    You can buy something called a http://www.torqeedo.com/us/en-us/products/outboards
    They have only one major problem.... but may you can build something like it. I would get a used gas outboard and use the leg for your electric motor at the top. And don't forget you need to cool your electric motor too. Easily done with old waterpump.
     

  15. messabout
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    messabout Senior Member

    We are dealing with a reality which is power to weight ratio. The weight of the boat and its contents is a major determinant. For a low powered boat a flat bottom, hard chine layout is probably the best option.

    I reckon that a total load of not more than 150 kg, a boat with a bottom one meter wide between the chines, and a power system capable of about 3600 watts output, could plane at about 24km/hr (around 15 Mph) Those wild guesses are based on past experiences with little boats and low power.

    The most glaring problem is that 3600 watts translates to 150 amps at 24 volts or 75 amps at 48 volts and so on. That means that there must be some heavy batteries involved. Now we are back, full circle, to the power to weight factor.

    I can imagine a simple flat bottomed skiff made of Ocumee ply, maybe 4 to 4.5 meters long. Such a boat could be built to weigh 40 to 45 kg. That does not leave much weight allowance for the skipper and the machinery. The same boat with its' contents would be lighter and have a much longer range by using a 4 or 5 HP outboard.

    Agreed, the electric drive would be more pleasing if it could be made to work according to our desires.
     
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