Rectifiers do not charge ,
their purpose id to change ac current to dc current to run the electrical circuits connected to the battery
it is the voltage regulator that controls the charge from the stator of the motor
using a multimeter set on volts dc
connect across the battery and read the voltage ( 12--13.2 volts ) start the motor and increase the rpms to around 2000 rpm and read the meter
it should be 14.5- 14.8 volts dc
that indicates that the system is charging
if not , take it to a service center that has a marine electrician to fix the problem