Propeller in the manufacturing process of the different geometric shapes of the leaves, will cause the blade weight ranging from the blade angle, the pitch does not meet the requirements of the drawings and so on, making the propeller center of gravity is not in its rotation axis, resulting in static imbalance. In operation, due to the ship stranded, or with the collision of hard objects, or the material itself defects, resulting in leaf bending, curling, deformation, and even fracture. So that the propeller out of balance. When the propeller is out of balance, there will be anomalies in the shaft, host and hull. Experienced crew will immediately notice the shaft will be beat, the boat bearing a percussion, the host speed is uneven, the hull also has abnormal vibration. For example, a ship sailing on the East China Sea on the sea, was calm, the host in the sub-sub-normal operation, suddenly hull vibration, pay attention to immediately turn to the sub-shift, then found the last three intermediate bearings have obvious percussion until Down to turn points, percussion disappeared. At that time, it was found that the spin propeller did not take the water. After the break, with the wheel method to view the propeller, found that there are four leaves in the leaves of the root off. The loss of the propeller in the shipyard, with the ship and the ship survey sector is not uncommon. Serious damage caused by the balance of the screw caused by maritime accidents. Where such accidents occur, should the propeller underwater or dock inspection, and then determine the repair or replacement. To ensure sailing safety.