Hi Everybody,
I’m think about converting our 41 feet (32 waterline) sailboat to electric propulsion.
Currently there is a Perkins 4108 in place with a power rating of 36 kw.
Below is a graphic for the power requirements for our type of boat at a given speed.
My current use of the diesel is that I don’t go over 2500rpm what results in 5.5 knots (calm waters).
According to the chart below this brings me to a power requirement of a little less then 5kw.
If I would install a 10kw electric that would still give me some reserve to reach more power on the prop for whatever reason.
E.g. full throttle would bring to aprox 6.6 knots in calm waters.
As you can see the power requirement to reach hull speed are enormous. This is never my goal and if I like to reach hull speed I do that with the sails or stick with the mentioned speed if there is not enough wind.
Of course I could go with higher power motor but then charging off grid, planned 48v system, is a lot more complicated in regards to reach higher voltage like 72v which you would need for higher power motors.
What are your opinions?
2011 Beneteau Oceanis 46 for sale in Greece
Just realize that if you want to run a constant 5.5kts that you are correct, you’ll need a 10kW+ motor. Most electric motors are rated at their max output, not their continuous.
For instance we have the Oceanvolt servoprop SD-15 system and run them at about 1/2 power giving us 5-6kts in calm water. They are rated at 15kW but will only run for 30min at that power requirement. (Honestly the space might get warm enough that the motor controller will throttle them back.) That said we can run them at 12kW continuously. This gives us a speed of 8-9kts but at a HUGE energy cost.
So I recommend going double the power output of what what you think you need. This will ensure you have enough power to meet your needs.