RedactedNarrative: Operator launched his vessel and was driving and decided to turn around due to weather.  While he was transiting back to boat ramp he took a large turn and heard a loud noise from the engine.  He lifted his engine to inspect damage and noticed his prop was damaged along with the engines lower unit.  He lowered his engine to the operating speed and continued at a slow speed to ramp.  Operator said the channel was poorly marked and that morning was an extreme low tide.