The few ones Ive seen are a direct bolt or 1 to 1 ratio. I dont know if the design was just lazy or efficiency was out the window when it comes to boats anyway.
I read some books from amazon about electric boats and it said hull design was the most important for efficiency. Next up was propeller design and motor. You needed to know the graph to your motor and setup the voltage to run at that rpms.
I use to cruse the lake not too far from me in a small boat with a small gas engine. I often went half throttle tops. Then one of those guys with a power boat came through. Boy it went a shock wave through the water that took forever to go away.
