Generator to electric motor outboard

Discussion in 'Hybrid' started by carl_rhino, Jan 3, 2015.

  1. carl_rhino
    Joined: Jan 2015
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: UK

    carl_rhino New Member

    Hi everyone,

    I have an idea I'd like to put together in one of my speedboats. I want to replace an outboard engine motor unit with an electric motor, powered from an inboard mounted generator. Am I mad or is this perfectly possible?

    Obviously I want to go stupidly quick - it's a speedboat - but I'm also after huge running times between tank fill ups. I have on an board fuel tank, so I'm also thinking of hooking that to the generator so that I can just keep going. Currently a 50hp outboard is the recommended unit for power, but that just drinks fuel - there must be a better way.....

    Ideas anyone?

  2. P Flados
    Joined: Oct 2010
    Posts: 604
    Likes: 33, Points: 28, Legacy Rep: 390
    Location: N Carolina

    P Flados Senior Member

    Have you looked at available hardware.

    Typical generators and motors are not high efficiency. At the cheap end of the spectrum you will lose about 15% each. At the high dollar end you might lose 8%.

    So that means for the same shaft output, your primary engine will need to put out 1.2 to 1.4 times what an outboard engine would have to put out.

    Then there is the extra weight.

    Using an engine - generator with a remote motor make sense in some specialty applications.

    However the downsides are extra cost, complexity and efficiency losses.
  3. gonzo
    Joined: Aug 2002
    Posts: 16,572
    Likes: 1,557, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    It can be made to work. However, it will use more fuel, be heavier and cost more. If you want to go stupidly fast and feeding a 50HP outboard is a problem, maybe high speed is beyond your budget.
  4. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 148, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    To replace the 50 hp outboard you need a 40 KW generator, only available as a diesel, 5 times heavier than the outboard.
    The extra losses have already been pointed out by other posters.

    The answer to your question: YES, you're mad!
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,039, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Talk to the bloke who was going to power his boat by hydro-electric turbine generation from the wake of the vessel. If he has it operating successfully, you are advised to proceed with his concept, otherwise not ! :D
  6. essenmein
    Joined: Dec 2014
    Posts: 40
    Likes: 10, Points: 0, Legacy Rep: 75
    Location: halifax

    essenmein Junior Member

    You could do it, won't be cheap though.

    BLDC motor and controller, probably need less e motor power rating than gas due to its power delivery. Then lithium battery bank to smooth out your peak and average power consumption, then a small gas generator to keep the bats topped up.

    Really though a 4 stroke ob is the better solution, and much cheaper than doing the e conversion in a way that actually works.
  7. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 117, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    Good one.

  8. Sleipnir
    Joined: Jun 2014
    Posts: 28
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Central Europe

    Sleipnir Junior Member

    Nope, there's not.... at high speed your cheap, simple and relatively lightweight gasoline outboard is by far the best option.

    If you had said you wanted to go slow (4-6 knots) for prolonged periods then a combination of electric outboard, a battery+charger and a small generator makes some sense. Throw in a small solar panel to recharge the battery for free when you don't use the boat.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.