40 HP Merc Charging Issues

[Nucknoilerfan]

My fishing buddies' 40 hp Merc appears to have a charging issue. As I'm not all that familiar with marine charging systems I thought I'd leave it up to you folks to diagnose. While running the voltage on the guage shows around 12 volts and drops off the longer the boat runs. With an automotive charging system the guage should show over 14 volts and maintain that for as long as the motors running as this shows what the alternator is putting out. I'm assuming that a marine charging system should work much the same way. Does a boat motor contain an "alternator" or what is the proper name of what supplies the charge for the battery? Or does this appear to be an issue with a voltage regulator? Oh yeah, the battery is brand new and the motor is about 4 years old.

 

[Nucknoilerfan]

Re: 40 HP Merc Charging Issues

OK, now that I've done some reading and trying to understand this marine electrical charging system. How do I troubleshoot where the problem lies? Can I test the Voltage regulator or the Rectifier separately using a volt meter? Or is this something that needs to be looked at by the local marine repair shop? Seems like these are common problems on mercury outboards.