In a personal watercraft with an engine 17 disposed at a central portion of a craft body and a water jet propeller 18 disposed at a stern of the watercraft, a propeller shaft 33 of the water jet propeller is connected to an end 31 of a crankshaft of the engine by a shaft coupling 32. Applications may include use in any space, including but not limited to, intra-abdominal cavities, intra-thoracic cavities, and intra-cranial cavities. Each policy for an electronic transaction includes a permission to access a physical space or item by a user.