Abstract: In a variable propeller for a boat, variable-diameter main blades and stationary subsidiary blades are mounted on a propeller boss in order to provide further enhanced low-speed driving property and high-speed and high-output performance. When the main blades are in closed positions in which the propeller diameter assumes a minimum value, the main and subsidiary blades are axially superposed on each other. When the main blades are in opened positions in which the propeller diameter assumes a maximum value, the main and subsidiary blades are arranged in a relation such that their blade surfaces are substantially in line with each other.

Abstract: In a propeller for a boat, a plurality of stationary blades and a plurality of variable blades are alternately disposed around an outer periphery of a propeller boss. Exhaust passages are formed in the propeller boss to axially pass through the propeller boss at location corresponding to the stationary blades. Despite the provision of the variable blade which is variable in diameter or pitch, the exhaust passage can be formed into a large sectional area in the blade boss without being obstructed by a blade shaft for the variable blade.

Abstract: A plurality of blade shafts spline-connected to bosses of a plurality of propeller blades are rotatably carried on a propeller boss parallel to the axis of the boss, the propeller blades being rotated so as to increase the propeller-diameter D according to an increase in the centrifugal force, and all the blade shafts are mutually connected through a synchronizer including cranks integrally continuously provided on the blade shafts and a single common synchronizing ring. With this arrangement, it is possible to always equally control opening angles of all the propeller blades despite any partial conditional change.

Abstract: A propeller for a boat having a plurality of recesses and a plurality of land portions arranged circumferentially alternately around an outer periphery of a propeller boss which is fitted over and connected to a propeller shaft. A boss of each of propeller blades and each of blade shafts disposed parallel to an axis of the propeller boss to rotatably support such propeller blade are accommodated in each of the recesses, and each of the land portions is provided with an exhaust passage extending axially through the land portion to permit an exhaust outlet in a body of a propelling device to be opened at a rear end face of the propeller boss. Thus, it is possible to discharge an exhaust gas from an engine through the inside of the propeller boss into water.