New Alternator putting out 11.8volts?

[gjswt19]

2002 Moomba Outback V
310 Indmar TBI

I replaced my alternator because I kept draining getting low voltage. I installed the new alternator and it still is putting out 11.8 volts. I have tested both batteries and they are fine. I noticed that the purple and red wire that plug into the regulator on the back on the alternator shows 12volts before I turn on the ignition, but when I turn the ignition to the on position the voltage drops to nothing. I am not sure if this is wrong or not but if it is what could be the culprit and what should i check??

any advise helps

thank you.

[maxpower220]

What is the voltage output of the alternator when the engine is running at idle? and at about 2000 rpm?
That info is needed.

[gjswt19]

at idle it is putting out 11.8 to 11.9, and then at about 2500rpm it drops to 11.7 to 11.5

[EarmarkMarine]

Are you sure that you aren't running the boat solely off the batteries at this point which would draw more current at higher rpms and thereby reduce the voltage?

[Rugburn]

I had somewhat the same issue until I put every component of my audio on the exact same ground (engine ground). I had multiCD unit, head unit, iPod box, two amps, all hooked to the same ground. Before I had them near each other and noticed I wasnt getting as much from my alternator. Just my 2 cents.

[c.rix]

check your hoses make sure the belt isn't getting wet and slipping I had a similar problem found small holes in the J hose that goes from the water pump to the thermostat

mastercraft dealer had 5 in stock so I would assume its a common problem

also check the belt its self for abnormal wear if it is getting wet