+2 on that. I have Balmar external smart regulators on both engines. No doubt the technology had improved since mine were fitted several years ago, but they are the way to go. Most applications don't need a larger alternator, which generates more heat, uses more power, and often requires a second Vbelt and all the hardware going with it, as pointed out above. What works better is a smart regulator which makes more efficient use of the available alternator power. This also requires removing or disabling the internal regulator which is built inside the alternator.
The benefit of smart external regulators is that you can program the charging curve, which is determined by the regulator, not the alternator, and have both rapid charging and avoid overcharging. There are several manufacturers that make external regulators, but Balmar have been at this longer than anyone else, and based on my experience, I'd recommend their products. Unless you are very good at wiring and understand marine electricianry, if that's a word, this is something a professional should do- at least the part where the alternators are changed over to external regulation, and the external regulators are installed and connected to the boat's wiring loom.
