A Diesel engine for a small commercial boat operates at 200 rpm and delivers 800 hp through a gearbox with a ratio of 4 to 1 to the propeller as shown in figure below. Both the shaft from the engine to the gearbox and the propeller shaft are to be solid and made of heat-treated alloy steel. Determine the minimum permissible diameters for the two shafts if the allowable shearing stress is 20 ksi and the angle of twist in a 10-ft length of the propeller shaft is not to exceed 4°. Neglect power loss in the gearbox and assume that the propeller shaft is subjected to pure torsion. Motor Gear Propeller