boat bogs down when accelerating

I HAVE A 1995 BASS TRACKER DEEP V16 WITH A 60HP MARINER ENGINE.MOTOR HAD BEEN RUNNING GREAT ALL MORNING.LATER IN THE AFTERNOON GET READY TO RETURN TO BOAT DOCK & BOAT WOULD NOT ACCELERATE.STARTS UP FINE WHEN TRING TO ACCELERATE WILL BOGG DOWN,WOULD ONLY GO 5 MPH WHEN TRING TO GO BEYOND 5 MPH WOULD BOGG DOWN.VERY LONG TRIP BY TO BOAT DOCK WHEN 2 MILES AWAY!PLEASE HELP. THANKS