Price offer BLDC and other thoughts...

Discussion in 'Electric Propulsion' started by Runhammar, Jul 29, 2020.

  1. Runhammar
    Joined: Jul 2020
    Posts: 21
    Likes: 0, Points: 1
    Location: Stockholm

    Runhammar Junior Member

    Hi everyone
    I am converting a 29ft sailboat to electric, as part of a renovation. The choice of motor, voltage, type pf current etcetera is a big discussion and right now I am gravitating towards a 5kw Brushless Direct Current motor. Thoughts of alternatives are wellcome. (someone said, for instance, that a brushed motor would allow me efficiency in lower rpms, thus elimination the need for a gear to shift the rpm down. They do need maintenance, but perhaps that is more feasible than the gear arrangement?)

    I have been offered a kit from an importer here in Stockholm/Sweden and would like to have your opinion on the value. I have asked him for make/brand and origin and am waiting for his response. In the meanwhile lets just assume his products are of good standard. He is a well respected dealer and have been around for over ten years with many, it seems, happy costumers. He offers a two year warranty.
    Here is the offer:
    Motor: 5kw 48v BLDC: 1 300 euros
    Controller (for this motor, that will allow regeneration): 1 200 euros.
    A casing in stainless steel that will hold engine and gear to shift the rpm down: 750 euros
    Above mentioned shift/gear: 300 euros

    Are these prices what one should expect to pay, or will I benefit from shopping around? I am reluctant to pay 750 euros for the casing, which I think I can build myself, but the rest seems reasonable.

    Per Runhammar
  2. alan craig
    Joined: Jul 2012
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    Location: s.e. england

    alan craig Senior Member

    You definitely will not need changeable gear ratios. If 5kW is the continuous power and your propeller is (say) 75% efficient you need to find how fast your boat goes when absorbing 3.75kW and then find the propeller that matches this power and speed; then choose a reduction ratio that matches motor speed to propeller speed. I know there is a program called Michlet which can predict power if you can input the lines of the boat. The battery system and charging system will probably be more expensive than the motor and controller.
  3. KeithO
    Joined: Jul 2019
    Posts: 325
    Likes: 66, Points: 28
    Location: Michigan

    KeithO Senior Member

  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    You will also need a two way thrust bearing and mount for the shaft.

  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Did you modify the hull or will she still sail?
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