The commercial pilot related that he was preparing to depart on a local personal flight, operating under Title 14, Code of Federal Regulations Part 91. He wrote in his report to the NTSB that he was attempting to start the float-equipped airplane's engine while standing on the left float by hand-propping when he was struck by the prop. The pilot stated “I swung the prop, the engine caught, and the aircraft swung slightly left in a collision course with the dock.” The pilot received serious injury when he stuck his leg in the path of the propeller while attempting to prevent the airplane from colliding with the dock. He indicated that there were no preaccident mechanical problems with the airplane. The pilot noted that the accident could have been prevented if he had started the airplane by standing on the right float as he normally does, or by shutting the engine off before trying to avoid the collision.