Thank you thank you for your attention here.
Yes I am imagining a direct battery to motor power transfer, with the batteries being charged from an on-shore battery bank while the boat is moored at night, rather than a diesel to electric conversion that S Benji was addressing.
So 35 us gallons of fuel = 5128 megajoules of energy
A Diesel engine at 20% efficiency is going to apply 1025.6 of those megajoules of energy to the motor
An electric motor at 90% efficiency drawing power from a battery pack at 85% efficiency is going to apply 3922.9 megajoules to that motor.
(5128 x .9)x .85 = 3922.9.
Is that correct? Is that an oversimplification?
If the desired end product is about 1000 megajoules then is 285kwh enough?
That seems so much more doable. Thanks for helping me stumble through this. Your insight and math skills are really valuable.