A little more info might be helpful?
It sounds like you have a smaller boat with either no motor or perhaps an outboard motor. If your only runing fans and running lights, I would think a deep cycle group 27 of around 80-90amp. would be plenty. That should give you many hours for your usage. As far as recharging, it doesn't sond like you have an alternator on your motor or an aux. charger wired into your boat. I would simply find myself a charger from the marina, they come with aligator clamps, clamp on, plug it in and charge your battery once a week or so. Your not drawing a whole lot with fans, you should be just fine.