You are absolutely right. I'm not aiming to create something practical with real range and daily usability - If i could I'd sell the concept and never work another day in my life
Indeed Weight and economy of scale is the enemy. Real usable electric/hybrid boats exist in the 10ton+ range, where 2000kg batterypacks don't ruin the boats performance.
Some of my calculations:
i took the Flying Saucer 190lbs hull for this example: Electric only:
Misc Stuff(Vests,Oars,Beer): 10Kg
Total: 200Kg Electric + 2KW Generator + Charger:
Total: 224Kg 6HP 4-Stroke:
Total: 209Kg Drive Performance:
If I'm not mistaken current outboard Horsepower is rated at the prop? so an 6HP will at some point deliver 6HP to the Prop.
My planed Drivetrain Specs for Electric:
PMSM 25KW(peak!) Motor
90V 800A Controller
Custom 2KWh 72V Battery Pack
Prop Power output and runtime estimations factoring 80% Drivetrain Efficiency 16,3KW(22hp) for 4minutes
10,8KW(15hp) for 9minutes
2,7KW(3,7hp) for 32minutes
All calculations are done with measured Cell/Battery Data(not claimed specs). Thats why going from 10 to 16KW cuts the runtime in half as the pack aproaches its limit. But to be hones i have no idea if my speced motor can even survive 16KW for 4minutes.
For the heavy configuration with the 2KW Generator ther is a gain of 1-1.2KW in output Power. 1KW gain will not upset the 24Kg wight penalty but ads a little cruisability.
So Going for Max Range with the generator running 3,7KW for roughly 30minutes
. Keep the Generator running and 75minutes(or a swim and two cold ones) later its ready for another run.
This is not an ideal configuration, but one that fits my budget.
Better would be add 3more Batterypacks(using Highcap vs Highdrain cells) for a total of 9,5KWh of energy storage and run with generator and 4-5KW output for over 90Minutes.