How about that 80kW DC diesel generator instead of that wing engine? 80 kW is just a rough estimate, but it should equal conventional 160 hp wing engine pretty much.
Have backup propulsion as a 80kW electric motor driving the same second shaft with folding prop, or even more ideally 2 smaller similar 40kW props / underbody pods so that the thrust is symmetrical? This backup propulsion is always available within seconds, if two shafts / pods maneuverability comes as a free bonus.
Could also have a backup / aux motor on main shaft for entering / exiting marinas in priceless silence.
Then for the generator loading, have a sufficient battery bank to absorb full output of generator at 1C max, ideally 0.5C. Then generator only runs for a short time, and all the hotel loads are supplied by an inverter.
This approach could certainly be made to work, and is a good example of one I considered.
Here's how it works out in a bit more detail.
First, a 160hp propulsion engine in a generator would be 100kw, using Northern Lights as an example. Let's stick with that so we don't compromise emergency propulsion speed too much. It's less available power because the engine that produces 160hp at 2300 rpm for direct propulsion, produces less at 1800 rpm generating electricity. That 100kw turns back into 130hp in an electric motor, but let's assume it's close enough. Physically, it's the same size as the wing engine and gear that it would replace.
Now I need to electrically power my loads, so let's look at them one at a time. Note that the generator is 440/240V, three phase.
Propulsion: I want to use all the available power, so I need a 130hp electric motor. That's a big motor - about 24" diameter and 48" long. And it weighs 1800 lbs. Cost is about $17k. It will also require a VFD, and a mighty big one at that. Physical space is probably half again what the motor is. Cost? I don't know? I'm also assuming that there is no reduction gear and that you can prop to match the motors 1700 rpm speed. If you need to run slower than that, like to match the 1000 rpm shaft speed of the traditional wing engine, you would need a larger electric motor to get the desired 130hp at a lower RPM.
Hydraulics: I need nearly the same power as for propulsion, but let's say I can go down to a 100 hp motor. That's a bit smaller at around 20" diameter and 40" long, and weights 1300 lbs. Cost is about $14k. And we need another VFD to drive it.
Battery charging: I'll assume a 48V system. 100kw of charging at 52V (operating voltage of LFP) is about 1900A. That's a fork load of current. Typical chargers are 100A, so I would need 19 of them. At an estimated $2k each, that's about $40k in chargers. To constrain charging to 1C, that means 100kwh of batteries which is $100k, give or take. But all the LFP manufacturers call for .3C to .5C, so if I keep it to .5C I need to double the battery bank side to 200kwh, or only use half of the generator's capacity. I would probably use half the capacity, and also reduce my chargers from 19 to 10.
Inverters: Now I assume we want to run the electric stuff off of batteries, so we need Inverters. First blush would suggest 100kw of inverters. Even if you could get a 10kw, 48V inverter, you would need 10 of them running parallel. Someone probably makes that, but I don't know who. And keep in mind that the generator, VFDs, and motors are all 440V 3 phase, so the inverters probably need to be the same. Estimates cost, $50k.
House loads: Yes, those pesky 120V house loads. You would need to sort out how to spread the loads across the three phase power system, and you would need a transformer(s) to create 120/240 split phase, assuming a North American house power system. If it's a 230V single phase house system it's a bit easier.
My take is that it gets complicated and expensive very fast, and for no obvious gain. It can't do anything that the traditional system can't do. It takes up the same or more physical space. It costs a lot more money. And there is a lot more to go wrong, and requiring spares. Yes, I could silently approach and depart a dock. But I can buy a lot of muffler and sound proofing for less $$, and with less space. And sound proofing doesn't break in disabling ways.
