@Ed_Johnson - the paddle wheels are drag, the paddle wheels for PP are small, and spin freely, so they aren't too restrictive, but the moment you couple them to get power, they're going to take more gas to push through the water, than they will regenerate in power. That's just physics, no matter how low drag the output will be lower than the drag. If you had flaps that opened/closed the flow to those, perhaps you could wrangle it, but boats decel so quickly when you chop the throttle that the amount of energy you could possibly get per pass are very low.
The start stop feature - unfortunately we utilize our engines to do lots of maneuvering for skier safety, don't want the engine shutting off while you are trying to maneuver around a downed skier for instance, no brakes! And most Hybrids you have a small engine and an electric motor as you only need the electrics 90% of the time, with the gas for accelleration and highway runs at high efficiency, our boats are backwards, you'd need the combined system for everything but low speed maneuvering.
What boats NEED is that system V8's in trucks have where the engine cuts compression/fuel/spark to cylinders not in need, so you could idle around on two or four cylinders, then when you pull the skier up you are on 8, when you are in the course it could cut consumption as needed, and you avoid all the extra batteries etc. Nice lightweight aluminum V8 engine with engine management software to save fuel, but I really suspect it will be primarily on V8 mode, as tow boats are super inefficient.