Electric Motor as Wooden Boat Option

Discussion in 'Boatbuilding' started by sshhss, Sep 7, 2021.

  1. sshhss
    Joined: Sep 2021
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    Location: Summit Lake WI

    sshhss New Member

    I am building a 15 foot cracker box wooden boat, what kind and size of an electric motor would work for this application. Top speeds would be around 25 to 30 MPH.
     
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum Sshhss.
    Are you planning on using an inboard engine or an outboard engine?
    Which ever, your top speed sounds rather ambitious for an electric engine - you will need to have a large battery bank, and I doubt that you will be able to run at 25 knots for too long.
    Changing tack slightly, as you have started this thread about your Cracker Box, would you like to post some photos and stories about her construction so far please?
    We are all very keen on posts like these. :)
     
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  3. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    Boats don't care what turns the prop, you need the same size electric as the gas engine, electric horses are not bigger. As to what kind, there are inboards and outboards, it's up to you.
     
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  4. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell "Whatever..."

    Size: 30kw should make 30 MPH depending how big you make your lightweight lithium battery.
    Type: Brushless motors are good but don't forget you need a charger and a speed controller too.
     
  5. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    There are a few high performance boats with electric propulsion; the downside is that they won't go very far at high speed before the charge is used up. If you were heading for the far side of a great lake it might not get there. Unlike an IC boat the weight doesn't decrease as the energy reserve is consumed. I expect a bit of googling will bring up examples of boats with a similar level of performance.
     
  6. duluthboats
    Joined: Mar 2002
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    Location: Minneapolis,MN, USA

    duluthboats Senior Dreamer

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  7. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    Welcome to the forum.

    I'm interested in the subject of electric propulsion, so I'll follow along. Sorry, I wish I had more to contribute.

    +1
     
  8. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    An ELCO 30HP sells for about $7,000. The 8 battery pack is about $4,000 and 7,000 lbs. The controller, charger, etc. about $3,000. It won't get the boat at the speed you want, unless you only install a small Li Ion battery to run for a few minutes.
     
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  9. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    @sshhss Gonzo's post above is suggesting that regarding propulsion, you would be much better off (especially financially) by simply installing an outboard engine on your Crackerbox.
     
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  10. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    And herein lies the problem. The costs are exhorbitant; the outcomes less than ideal. If you buy a wrecked Tesla battery; you might be able to make it more affordable, but still 15 grand for 30hp is $500/hp.. And 15 is low..
     
  11. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    From the Elco Website:
    EP-30 Electric Outboard - Elco Motor Yachts https://www.elcomotoryachts.com/product/ep-30-electric-outboard/
    EP-30 Electric Outboard
    $6,999.00
    Voltage: 96 Volts
    Suggested Battery (Ah): 130 amps DC
    Comparable HP: 30HP
    Required Accessories:
    Battery Connection Kit $295.00
    (You need this kit to connect your outboard to your batteries).

    Battery Monitor | Victron BMV 700H $728.00
    (This monitor is used to see how much charge you have left in your batteries).

    Panther Electric Trim & Tilt $650.00
    (This is a remote-controlled tilt to lower and raise your outboard from the water).

    Deep Cycle Battery Charger (Elcon UHF3300) $895.00
    * Deep Cycle chargers are only compatible with Deep Cycle Batteries.

    Recommended battery pack:
    Deep Cycle AGM Batteries (8x)$3,936.00
    96 Volt Power Supply
    8 Batteries - 12V/165Ah | L-19.1" x W-6.8" x H-9.4" | 103lbs. ea. X 8 = 824lbs

    Their biggest battery offered:
    Victron 12v AGM – 220Ah
    $585.00x8=$4680.
    Weight: 65kg = 143.3lbs (x8) = 1146.4lbs.

    I don't know where Gonzo got his number for the weight, but it's still pretty excessive.

    -Will
     
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  12. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Forget Gonzo's typo. What is more important is run time.

    Am I correct in understanding one hour at Wot for option one or a bit under two for option two?
     
  13. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    A couple of things should be evident from the numbers presented.First the weight of the installation will immerse the hull quite a bit and an existing design might not work well with the burden.Second,the modest power mentioned may struggle to get all that weight moving quickly,or if it does it won't be doing it for very long.There may also be a need to arrange to keep the battery pack cool if the maximum output is being drawn.
     
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  14. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    Maybe, but I don't see the amps rating for the motor, so you can't tell from those numbers.

    [ Edit: maximum current is 130 amps. ]
     

  15. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    130 amps
     
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