Jon W - it could be that your batteries
were already full. If they were, their acceptance level would reduce the amount of juice they could consume, and the amps would be expected to be lower. You'd get max amps out of any alternator when the batteries need a (full) charge and can accept the amperage available.Benny's description is very good and represents what I've heard called the "steadily diminishing law of returns." He needs to and plans to plug in every few days. Even if you have an inboard diesel engine (and I understand you DO NOT, but stay with me) unless your alternator and regulator package can produce a daily dose of amp output to meet your daily amp hour draw in an hour or so, you'll end up eventually drawing down your batteries because you'll be taking more out over the course of a week than you can return, because you'll most likely NOT want to run the engine more than an hour a day (at anchor). If you're motoring a lot, this is a moto point, but these are sailboats. Hence the need to go to a marina to plug in on a regular basis. We've recently installed a new alternator and regulator and have determined with our energy budget that an hour of motoring will equal our daily use. That's a good balance. Additional improvements would be a larger solar panel.So, as Benny describes, do an energy budget, do some reading, and figure out how YOU intend to use your boat. Your boat, your choice, and you do have many choices.