Re: [electricboats] 48V 10kW vs 20/30hp ICE

I have converted a 12,500 lb boat to electric replacing a very well matched 23HP diesel with a 12kW water cooled electric motor.  I have a lot of detail on my installation here:

http://dan.pfeiffer.net/10m/electric_drive.htm

Look it over.  I'll just say a couple things here in response to previous comments...

I would recommend over-building capacity so that at cruise speeds you are operating at about 50-60% capacity.    And you can't run too cool.  Have as much passive cooling as possible in addition to an active cooling system. 

I don't think you would need 15kW to replace a 20HP diesel (if that was a correct match to the boat).  I replace 23hp with 12kW and I think 10 might have done it but I wanted more capacity headroom and I wanted water cooling which I got with the Motenergy ME1616 motor.  See my details in the link above. 

The propeller is very important to get best performance.  Bigger and slower is better.   Spend some time on this.  I have a feathering prop and it can do regen.   A folding prop would not.  I have seen 500 watts sailing at 6.5-7 knots.  It's a bit tricky to keep the throttle adjusted for best output.  But a computer could do it pretty easily. 

The comment about low RPM torque in the electric as relating to acceleration of the motor is true enough but otherwise basically useless in this application.  If you ramp up RPM too fast all that torque is just going into making bubbles and that cavitation is probably pretty hard on the propeller.  So the quick acceleration of the motor is not really all that useful if you cant get that power to the water.  Like having tiny tires on a 700hp car. 

You need to design the driveline system to get the motor operating in it's best efficiency range at cruise speeds.  Yes you can get all that torque at half RPM and drive a big prop.  But you'll be wasting a lot to heat if the motor is not close to that sweet spot.  With the motor I have and similar motors I don't know how you could do it without a reduction gear of some sort.  Mine is a 3:1 belt drive.  On the diesel it was 2:1 gear.  Same max RPM of 2400.  So my max prop RPM went from 1200 to 800.  The feathering prop has a changeable pitch.

The low speed operation of the motor is a nice advantage over diesel as noted.  The low rpm speed of diesel is limited to the idle speed of the engine.  700rpm?  The electric is fine down to 1 RPM.  As noted it is useful is docking type operations.


Dan Pfeiffer

On 2022-06-23 9:01 pm, Jeffrey Griglack via groups.io wrote:

 

I replaced my Atomic-4 (rated at 30 hp, but probably, really closer to 20) with a 10kw kit from Thunderstruck.  It worked well in my Pearson 30 (30 feet, about 8300 lbs. displacement) sailboat.  I was limited by the small battery bank, but it got me in and out of the cove where my mooring is located.  I used the same prop that I was using for the A-4.

 

I since upgraded boats to a Pearson 365 (36.5 feet, ~18000 lb displacement) with a Perkins 4-108 in it.  The diesel runs well, but is 43 years old, and I am thinking I will, at some point, replace it with a 14kw, 72v, liquid cooled electric at some point.  I figure I should be able to mount the motor where the v-drive is currently, and the batteries where the engine is.  But we'll see.

 

On Thursday, June 23, 2022 at 12:53:55 PM EDT, Rumble <rumble@bigpond.net.au> wrote:

 

 

Just wondering if anyone can give real life experience with replacing a 20hp or 30hp diesel with a 10kW 48V electric motor diy. I am aware of the conversion and inefficiency allowances etc, but in actuality, is it more like a 20hp or 30hp, assuming same prop and configured rpms etc?