Gensets vs Inverters
In my view a 38 foot boat is too small for a generator. The only circumstance where it should even be considered is if you have air conditioning. In that case it''s only because the power drain is just too great for any reasonably sized inverter or battery bank.
You can get 1000-2000 watt inverters which are very light and compact. Pro Watt makes a line. Heart also has a line of inverters, but they''re older technology (low frequency, requiring a bigger transformer) and much bigger and heavier. I believe Heart was selling the Pro Watt line at one time.
Dashew''s Sundeer line of boats (up to 65 feet or more) are designed for live aboard world cruising, and generally rely on big alternators, huge battery banks and an inverter to provide power, rather than a generator.
If you couple the inverter with an oversized alternator you can run the engine while the inverter powers big loads. In effect you have a generator, at much lower cost, and consuming much less space and weight. I have a 1000-1200 watt Pro Watt and use it that way all of the time. The bonus is that you don''t need to start the engine at all if the load is small or for only a few minutes. With a generator only you have no a.c. at all without starting the generator.
Diesel generators are very, very expensive. Non marinized gas generators are fairly inexpensive. The only way a gas generator could ever even be considered would be if the fumes could not leak into the bilge. This would probably mean leaving it on deck or draining all of the gasoline out of it. Neither is a good solution except for emergency or backup use only.