TwistedTree, I think you might be right on all points.
One of the main benefits of hybrid propulsion is the ability to provide an extra surge of power when accelerating. That's why it works for cars - we rarely spend more than a few seconds at high throttle in normal driving conditions to start from a red light, or get onto an on-ramp. It's also one of the reasons why diesel-electric propulsion is dominant for locomotives. You can get the acceleration you want without having to massively upsize the engine. For a long trip on the water, though, relying on fuel oil would be unavoidable.
It sure would look "greener" dockside though... which may well be the point. Not likely to be a material change in fuel consumption overall though. As you say, hull form improvements would be way more impactful.
Nigel Calder
(link) has a really interesting discussion of how hybrid power might apply to smaller pleasure craft (spoiler: not great).
The gist is, it doesn't make a lot of sense for a lot of use cases in cruising. If you're going distance, you'll be at constant revs and fairly high output for hours at a time. Having enough juice stored in batteries would be impossible, and the amount of solar cells required would be insane. So you'd need a suitably sized engine using conventional fuel to propel you along for most of the trip.
There is the Greenline line of hybrid powerboats
(Greenline website) which look quite fancy, but the range under electric-only is quite limited. Really it would be more of a day boat, or a way of getting in and out of dock/anchorage quietly and then firing up the diesel engines. Some sailboats go electric or hybrid for that use case.
The one argument I could see for a hybrid cruising yacht would be in canals and particularly locks where you're doing a lot of maneuvering at slow speed, with potentially a lot of stop/start cycles. That could be accommodated pretty easily because it's very low throttle. Or if you're just hopping slowly between islands at short range without wanting the noise/exhaust and low-rev engine hours. Otherwise trawlers are about the polar opposite (steady heavy load) of the profile that suits hybrid propulsion (peaky power demand with low average).
Jeff
