With a good inverter I don't think the 48V will be a problem.
I had a look and it seems they have plenty experience with barges in canals. Of course the efficiency on the sea would be less except in settles waters (that is the case many times when there are no wind at all) but what they say is impressive:
Our parallel hybrid concept allows you to drive the propeller with the engine in the normal way or alternatively to use an efficient electric motor. When moving under engine power the motor automatically reconfigures itself as a 5kW generator. At standard canal speeds, for every hour of engine propulsion, you generate enough electrical energy to go for a further hour under clean / quiet electric drive. In general our Hybrid canal boats see a 50% reduction in engine hours. ...
The best way to use the hybrid is to fire up the engine on open stretches to rapidly charge up your batteries. When your batteries are charged you can then switch to electric drive and enjoy the countryside in complete silence. It takes about 4kW to push a 60' narrow boat at canal speeds....
...Your hybrid is a portable power station. With the powerful generator capability, a substantial battery bank and inverter technology, you have an optimum power solution. Some of our boats take full advantage of this by being all electric (no gas onboard). Every domestic appliance you use at home can now be powered on your boat : Washer/dryers, electric oven & hobs, toaster, kettle, fridge/freezer etc.
Set the boat up with a normal domestic ring main and there is no need for under powered and costly 12V appliances. For those few items of equipment that need 12V you have a step down converter capability from the main battery bank. Forget running your generator at dusk/dawn to top up the batteries. The enhanced battery bank of the hybrid supplies, in complete silence, more than enough power for the night and can be charged again when you are under way the next day.
Why fit a Hybrid? - Hybrid Electric Marine Propulsion
If I was The Chef I would talk directly with these guys for more information since it is them that are on the basis of that particular engine modification to make it an Hybrid.
NB Chelonian Hybrid