Screw propellers, commonly known as propellers, are devices used to propel boats and ships through water. They consist of blades that rotate around a central shaft, creating thrust by pushing water backward. This movement allows vessels to move forward efficiently, making screw propellers a vital component in marine engineering. The design of screw propellers can vary, with different numbers of blades and shapes to optimize performance for specific applications. They are often made from materials like bronze or stainless steel to withstand harsh marine environments. Overall, screw propellers play a crucial role in the operation of various watercraft, from small boats to large cargo ships.