We (4 of us) did a lot of overnighting - even extended weekends in our Sea Ray Sundancer (cruiser). So likely, very similar use to what you are asking out. I used ONE deep cycle battery for the house loads and never ran it down. In fact, I once went 3 days and purposefully never switched away from the DC battery. I ran the engine a total of about an hour that whole time and still was able to start the engine just fine on the last day. We had the frdige running the whole time, some stereo use, lights at night and the all-around light on all night. All cooking was done on either on-board alcohol stove or the cockpit Magma stove. Point is, you can do quite a lot on a battery. If you wanted, you could put two deep cycle batteries in parrallel to double the run time.
This is not to say that I'm against a genny - you'll need that for AC - but you do have options. One last thing... a built-in genny will never be less expensive than ordering it with the boat... although it sounds like you're buying a boat that is already in stock at your dealer?
Before you consider (if you are, that is) a portable genny please read up on the safety problems with them. Every year, there are people who never wake up from the use of the portables on boats and RV's. CO poisoning is just one of the issues - and whether the genny is placed on the bow or the platform, CO can still enter the boat. Rather than list everything here, go to post #9 at the thread below. You owe it to yourself and your family to read the entire thing.
I'm kindof sick of the amount of maintenance and babying I have to do for my 2007 FP Mini4+ generator. For a handful of reasons this thing requires the capsule to be removed WAY TOO OFTEN to replace relays, troubleshoot, etc... Not to mention how I have to dislocate my shoulder to access the...
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