I like the idea of DC. If starting with a clean sheet, a good design for a boat system could be drawn up. Especially getting away from 12v and going higher to limit amps in cabling.
But the rub shows up in a few points:
1. Safety, not many have been killed by 12V, but get much over 24V and up, and now you can get zapped. I have been bit by 32V when sweaty and it could have been bad. I am quite sloppy with 12V and am still kickin'.
2. Switching. I know contacts running DC become more problematic with higher volts. I don't really know the details (mech engr here), but when I worked in power plants and submarines there were differences with AC and DC switching in the higher voltages.
3. Incompatibility with off the shelf household type stuff. Forces you to either buy specific for DC, or run a large inverter to run AC loads. Like aircon.
4. Forces some sort of conversion when on shore power, depending on how much AC stuff you have and how much is DC.
I looked at that DC gennie, I guess I don't understand how it is regulated. Output is DC, but then is variable speed. As I understand permanent mag gennies (really a rectified alternator, right??) if the speed changes, so does the output volts. That is what is nice about a unit with slip rings or rotor/stator variable excitation. Reg changes exciter volts, output volts follow.
PM gennie can be used with fast switching inverter tech (portable Honda) to put together a decent AC waveform. But that is AC, this thing is DC.
Interesting stuff, though.
Ski, I think you misunderstand.
The DC output of the generator is never used 'directly' by any device except the DC-to-AC converter (A.K.A. the common 'inverter') and (sometimes) a DC-to-DC converter.
If you are familiar with the newer Honda 1000i and 2000i portable generators (where the 'i' stands for 'inverter'), it is the same concept. These little generators produce a variable-voltage DC output which feeds an inverter, which is why they call them "inverter-generators".
https://www.consumerreports.org/inverter-generators/pros-and-cons-of-inverter-generators/
Now, in a standard 'oldschool' AC genset, the engine always has to spin at an RPM that produces >>exactly<< 60 Hz, so, for a 4-pole generator back-end this would be 1,800 rpm. If it's a 2-pole generator it would be 3,600 rpm. For european markets, 1,800 rpm/60Hz generators are spun more slowly to produce 50Hz at 1,500 rpm or 3,600 rpm 60 Hz generators are slowed down to 3,000 rpm. This generator produces alternating current by virtue of it's commutator-based design, and the current 'alternates' at a frequency dictated by the engine/armature rpm.
Bottom line, these generators produce a constant voltage and frequency, while the output >>current<< varies with load. The engine will be spinning at 100.00% of rated RPM even if you are only using 5% of the rated output power.
The new DC generators produce a constant
current, while the DC output >>voltage<< varies with load. Because the alternating current (and it's frequency) is produced by the inverter's electronics (and not by the spin-speed of the armature), the new DC generators can spin at whatever rpm is 'right' for the load, this takes advantage of the torque curve of the engine. So....if the demand for power is only 5% of rated load, the engine will spin very slowly. Likewise, the engine will spin faster as more juice is needed.
There is absolutely no safety issue because (a) at any given power level, DC in intrinsically safer than AC -- remember Edison vs. Westinghouse? and (b) the higher voltage DC goes directly to the inverter and it doesn't connect to anything else in the boat.
Hope this helps...