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My voltage is running 15 1/2 volts on my boat? - voltage regulator boat

This weekend, my blood pressure was 15 1 / 2 volts. Is typically 14 volts.
My boat is a Bayliner 1994 454. with a Mercruiser I wonder if my alternator has failed or the voltage regulator has gone bad. Volts at idle seems to be around 14, but when I give gas to go 15 1 / 2 volts. The boat has fresh batteries. I wonder if my alternator has a built-in controls in the view that it is independent or the alternator? Where can I find that the alternator I have in my boat? My boat is on a road about two hours and we had to leave before he had the information from the ship.