RUDDER DRIVES FOR MODEL BOATS; PROPULSION COMPONENTS AND UNITS, NAMELY, PROPELLERS AND PROPELLER SHAFTS FOR MODEL BOATS; RUDDER PROPULSION MECHANISMS, NAMELY, RUDDERS FOR MODEL BOATS, BALANCE RUDDERS FOR MODEL BOATS, SLANTING RUDDERS FOR MODEL COMPETITION BOATS, TILLER ARMS FOR MODEL BOATS, AND WATER SCOOPS FOR MODEL BOATS; COUPLING DEVICES BETWEEN PROPULSION ENGINES AND PROPELLERS IN MODEL BOATS