Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 24Get this manual
TRIM TRIMMING OUTBOARD "OUT" (UP)
WATER ABSORPTION It is imperative that all through hull fasteners be coated with quality marine sealer at time of installationWater intrusion into the transom core andor inner hull will result in additional boat weight (reduced boat performance), hull decay and eventual structural failureCAVITATION Cavitation is caused by water vapor bubbles forming either from sharp edge or angle on the gear case or from an irregularity in the propeller blade itselfThese vapor bubbles flow back and collapse when striking the surface of the propeller blade resulting in the erosion of the propeller blade surfaceIf allowed to continue, eventual blade failure (breakage) will occurVENTILATION Ventilation occurs when air is drawn from the water's surface (excessive trim out angle) or from the engine exhaust flow (wrong propellerpropeller hardware installed or gear case labyrinth seal worn) into the propeller bladesThese air bubbles strike the propeller blade surface and cause erosion of the blade surfaceIf allowed to continue, eventual blade failure (breakage) will occur