Electric Outboard Fabrication

Discussion in 'DIY Marinizing' started by rogerstrube, Jun 24, 2008.

  1. rogerstrube
    Joined: Jun 2008
    Posts: 8
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    Location: Punta Gorda, Florida

    rogerstrube Junior Member

    I will begin construction of a 34 foot motorsailor when my sailing catamaran sells (Millennium Dragon, Ocean Cat 49). Some of the concepts for this new boat may be viewed on my web site: www.wingsailor.com by clicking on the "Ideal Motorsailer" tab. It will be built in my hobby shop (click on "A Place to Work").
    With the price of fuel climbing rapidly (no real end in sight) I am considering electric power. I contacted "Ray's Electric Outboards" ( www.rayeo.com ) but he makes only a unit that uses a 6HP equivalent electric motor. By the calculations on my web page I think I need at least 30HP. Ray suggested I adapt such a motor to a standard OB lower unit. I am thinking a couple of Suzuki 90HP motors (with blown power heads) could be adapted as they take larger diameter propellers. The reason for the OB configuration is so that the lower units may be tilted out of the water when sailing and when moored to my dock. Any thoughts on electric power or adapting larger electric motors to standard OB lower units?
  2. Kaa
    Joined: Oct 2006
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    Location: USA

    Kaa Wanderer

    Electricity is a form of power, not a source of power.

    If you want a 30hp electric motor you will need a generator to supply it with electricity. Such a generator is likely to burn fuel.

  3. ben2go
    Joined: Jul 2008
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    Location: Upstate, South Carolina,USA

    ben2go Boat Builder Wanna Be

    Are you still interested in this idea?I really don't think you'll need 30HP electric motor.Remember an electric motor has more torque at a given rpm than a belch fire.Most sail boats that use converted OB's either use golf cart setups or electric vehicle set ups,and big battery banks with a big supply of amp hours.A small 1500 to 2500 generator or genset as a back up to charge the battery bank.
  4. rogerstrube
    Joined: Jun 2008
    Posts: 8
    Likes: 1, Points: 0, Legacy Rep: 26
    Location: Punta Gorda, Florida

    rogerstrube Junior Member

    Electric Outboard HP Equivalent

    I have located a 28 foot Kurt Hughes design (run about catamaran extended to 32') that could be used as the base for the boat I want to build. Of course, I need to sell Millennium Dragon before I start another project. The 30HP estimate would work well with this boat as the parameters are close to my friend's "Skeeter". The 30HP figure is plugged into the formula avaialble on my web site for estimating boat speed based on length, HP, and displacement. 30HP should all the boat to reach the target top speed. The torque and power generated by a 30HP diesel needs to be converted to the size and output of available electric motors. In addition, the type of electric (brushless?) and the optimum voltage (24v, 36v, 48v?) that are practical and reasonably safe for marine use needs to be researched. Lots of solar panels and a small generator were in the plan. If you can point me to any useful sites it would be helpful.
  5. Guest625101138

    Guest625101138 Previous Member

    If you are going for electric you need to be realistic about the target speed.

    The sort of stuff offered here will be marginal for your application:

    I think for practical reasons you will need a minimum of 72V system if you are working on 30HP.

    There is not much point in using VRLA batteries unless you are working on a 10 hour rate. I expect their weight would kill the boat. Hence your best option is likely Lithium.

    Here are some VRLA:

    For lithium some reading:

    Some lithium sources:

    I have built a 4.5kW outboard intended to operate off 48V to test components. It notionally has short term rating of 9kW. I did some simple testing on two small batteries that limited power to 280W but it still worked well. Post #5 on the linked thread shows my simple outboard test video:
    Some of the other information on the thread may be of interest.

    Rick W
  6. ben2go
    Joined: Jul 2008
    Posts: 183
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    Location: Upstate, South Carolina,USA

    ben2go Boat Builder Wanna Be

    The newer generation of EV's use AC motors instead of DC.DC is still used for the battery bank.An inverter is used to drive the AC motor.I'm sure you're familiar with inverters.They run 220-240 Volts AC with a 200 to 700 amp controller.

    This place does some marine work.

    This place also deals with some boat conversions.

    I tried to find a website where a guy replaced the power head on a 9.9HP outboard with a small electric motor.He had a 20' center cabin sail boat.Of course he only used it as a kicker.He had no main engine.I thought I had the site bookmarked.Maybe I'll run into it soon.

  7. Guest625101138

    Guest625101138 Previous Member

    The Mars motor I am using is a 3-phase AC motor with permanent magnets and hall field sensors for phase locking. It is really made for vehicle application and speed control is way better than needed. My motor will speed control below 60rpm. Will pull through your hand if you try to stop it turning though even at a few rpm.

    Virtually all of the model plane electric motors are 3-phase motors these days. The sensorless controllers would be ideal for boat applications because they do not need the hall sensors for fine speed control. Problem is that the largest controllers are limited to 40V and 100A. There are some industrial DC-AC speed controllers for induction motors but their price is an order of magnitude higher than the model plane stuff:

    A high efficiency induction motor for inverter use will set you back a bit:
    Probably worth it when you compare with something like a Mars motor.

    This explains sensorless field oriented control:
    It is really the ideal approach for boat control but I have not yet found a suitable sized system that is a good price. The main benefit is that you can use industrial type IP66 induction motors that have high efficiency and are robust. It also avoids the need to connect any hall sensors. This is the fiddly bit with the Mars motors and a likely source of problems given the small wires to embedded sensors.

    Rick W
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