The reason why the ship can't run fast in the water is because of the effect of water resistance. To increase the speed of the ship, we must reduce the water resistance. How can we reduce the water resistance of the ship?
Did you play with throwing tiles on the water? If you choose a thin tile, take a parallel angle close to the water surface and throw it hard, the tile will jump forward on the water surface. If you throw it at the right angle, the tile will slide far.
Tiles are heavier than water. Why can they slide on the water? Originally, when an object moves in the fluid, it will produce hydrodynamic force. It is the hydrodynamic force that prevents the tiles from sinking and can jump forward on the water surface. Based on this principle, the ship designer made a planing boat. The bottom of the planing boat has a certain slope and forms an angle with the planing direction. This angle is called the angle of attack. The planing boat is also equipped with a high-power power power device, so that the hull can sail at a certain speed, so as to generate hydrodynamic force and support the weight of the hull.
At the beginning, the planing boat sails at a slow speed. As the power of the power unit increases and the ship speed increases, the hull is lifted by hydrodynamic force. When the hull is lifted to a certain height, the planing boat will slide on the water surface. When the planing boat glides, the weight of the hull is no longer supported by the buoyancy generated by the water discharged from the hull, but by hydrodynamic force. Because the hull is lifted out of the water by hydrodynamic force, the wave making resistance, friction resistance and eddy current resistance are very small. Therefore, the small planing boat can drive very fast, and the speed can reach 40 ~ 50 nautical miles per hour or even higher, so it is called a speedboat.
According to the number of hull, planing boats can be divided into single hull planing boats, double hull planing boats and three hull planing boats. The single hull planing boat has only one hull, while the double hull planing boat is equipped with two hulls, and the three hull planing boat has three hulls. The middle one is the main hull and the next two are auxiliary hulls.
The cross section at the bottom of the planing boat is V-shaped. Although it will cause large splash during navigation, it will not cause large waves. According to the shape of the vertical section, the planing boat can also be divided into single-stage and double-stage. The curve of the vertical section at the bottom of the single-stage planing boat is continuous. When moving at high speed, most of the bottom of the boat body leaves the water surface, and only the tail of the boat is immersed in the water, which is subjected to hydrodynamic force to support the weight of the boat body. The curve of the bottom profile of the double broken stage planing boat is discontinuous and has two broken stages. When moving at high speed, the two broken stages, one in front of the other behind, are subjected to hydrodynamic action, and the steps at the bottom of the boat are allowed to enter air, which can play a lubricating role to reduce friction resistance and further improve the speed of the planing boat.
No matter which type of planing boat, the speed of sailing is very fast. If compared with ordinary ships of the same tonnage and horsepower, the speed is about twice as fast. In addition, when the planing boat taxis in the wind and waves, the swing range of the hull is not large, and the course is extremely stable. Because of this, taxiing boats can be used as patrol boats, torpedo boats, missile boats, traffic boats and sightseeing boats.
However, the planing boat also has disadvantages. Once encountering large wind and waves, its speed will become very slow, and the hull can not be made too large. Therefore, there are certain limitations in the scope of application.