Running aground is a common boating experience. Usually we twist a prop blade or chunk the skeg and continue on our merry way. But in the extreme case, hitting submerged objects can cost $2,000 to $3,000 to replace the entire gearcase. Mark Payne, an ORPM lower-unit specialist with 20 years of experience, drags a few victims out of the trash to illustrate how. "Thirty years ago outboards had shear pins to protect driveline components from impacts," he explains. "Then manufacturers decided that a rubber hub was a better means of protection, so shear pins went the way of the buggy whip. Rubber hubs work okay with aluminum props because the blades act as the weak link when you hit something. But everyone wants the superior performance offered by a stainless-steel prop, whose blades give hardly at all."