Ships use propellers to generate pressure difference and provide the motion in water. Nickel-aluminum bronze alloy is used to make them corrosion resistance. (80 Cu; 10 Al; 5 Ni; 5 Fe) is appropriate alloy combination when the propeller used in sea water. Its coefficient of thermal expansion is 9.4 millionth per Fahrenheit.
|Three blade propeller|
Number of blades depend on the capacity and the ships mass so that enough acceleration can be produced from the propulsion system. For heavy load and high speeds the blades are bolted rather than direct welding to the shaft hub.
A four blade propeller model shown here is categorized by direct welding the blades to the shaft hub rather than bolting. Such model are preferred only for low speed and medium capacity ships. The word propeller is used for ship driving system because they make the fluid flow in axial direction. The shape of the blades is one of the important identity of propeller which looks entirely different from turbines and anchors. The angle of the blades are always less than 90 degrees.
|Four blade propeller|