Was the boat having problems before changing the rectifier?
How old is the battery?
Could the new rectifier wiring be incorrect (meaning was it a simple job matching up connectors or wiring color)?
1'st, don't panic and rip apart things or buy expensive parts.
If the engine runs OK but does not charge the battery, the stator is probably OK.
I see a wiring diagram here, let me know if it is correct for your engine.
http://www.maxrules.com/graphics/for...thru91A_CD.jpg
Step one.
The two wires from stator to rectifier are shown as yellow or green/yellow.
You need to set your multimeter to read
AC voltage 100 or 200 volt scale or auto range.
Connect the meter with solid connections, alligator clips, or such.
One multimeter lead to each of the two yellow wires.
Do not rely on a person holding the pointy probes.
With engine running, the
AC voltage should be above 12
VAC (Volts Alternating Current) and fairly steady (if engine runs steady)