Retractable Rotating Saildrive?

[Rapanui]

You could of course substitute a mechanical drive for the electric motor, but that does quite restrict the possible locations of the second diesel. My thinking is that you would probably also have a powerful bow thruster and electric is the obvious choice for that.
Adding a Lithium battery bank then becomes a logical integrated system design extension. It means that the second diesel can be sized not for the peak load but the maximum continuous load allowing the batteries to cope with peak additions, and hence will more often be operated at a sensible load as it will only operate when the system demands charging once the SOC drops below a preset value and which can be at high charge power for short periods. Make the DC system high voltage say 48 or 96 volts, then you can power the electric drive motor, bow thruster, windlass and inverter with sensible sized cables and without needing local batteries. DC to DC converters can power the remaing relatively few 12/24V consumers. AC electric can then be the default for other domestics such as heating, aircon, cooking etc, thus eliminating LPG. Adding a second alternator to the main engine for charging the Lithium bank provides redundancy should your second diesel/alternator fail.

[Dockhead]

Originally Posted by Rapanui

You could of course substitute a mechanical drive for the electric motor, but that does quite restrict the possible locations of the second diesel. My thinking is that you would probably also have a powerful bow thruster and electric is the obvious choice for that.
Adding a Lithium battery bank then becomes a logical integrated system design extension. It means that the second diesel can be sized not for the peak load but the maximum continuous load allowing the batteries to cope with peak additions, and hence will more often be operated at a sensible load as it will only operate when the system demands charging once the SOC drops below a preset value and which can be at high charge power for short periods. Make the DC system high voltage say 48 or 96 volts, then you can power the electric drive motor, bow thruster, windlass and inverter with sensible sized cables and without needing local batteries. DC to DC converters can power the remaing relatively few 12/24V consumers. AC electric can then be the default for other domestics such as heating, aircon, cooking etc, thus eliminating LPG. Adding a second alternator to the main engine for charging the Lithium bank provides redundancy should your second diesel/alternator fail.

All good thoughts, for which thanks.

I WILL have the lithium bank and the large second alternator on the main. I will have electric cooking and a big bow thruster. But there's no point in driving the shaft with electric if I can hook it up mechanically. The second engine will be much smaller than the main so will operate in a very efficient range if I use it for propulsion.

I like it.

So simple I believe I could even manage it on my present boat.