What I think will work, and will provide a lot of the benefits of a 100% electric system, is a series hybrid diesel electric. If you run an 80 kWh battery (ie Tesla Model S long range) with a repurposed EV motor (150-300hp), you could have both good cruise range and the ability to motor out of tight situations at higher speeds. But you'd be dead in the water if you needed to use more power more frequently, so I wouldn't be comfortable with that trade off. Hence the addition of a diesel engine, perhaps fitted roughly where and how the factory diesel was, but spinning a genset instead of the prop. That genset would be charging the battery pack and running at max efficiency, since it'd be under consistent loading. Of course, the diesel could be off on slow cruise days, so you're running silently. Plus, dropping anchor with a full battery means you can run air conditioning all night without the thrum of a genset, cook with induction, and even heat with electricity, which means no propane on board either.
