A drive pod of a watercraft such as a boat may be designed to break off the hull of the boat in the event of an underwater collision involving the drive pod. A shaft assembly that transmits power from the engine in the hull to blades or a jet in the drive pod is designed to break at a precise point so that seals in the hull and seals in the drive pod are protected from damage. The shaft assembly may include an axial blind hole with an undercut at a bottom of the blind hole. A pin may be inserted to reinforce the shaft above the undercut.