Both water jet propellers and propeller propellers for speedboats have their own advantages.
Waterjet propeller: It is a propeller that uses the reaction of sprayed water to generate thrust. The water jet propeller is composed of a water pump, a water suction pipe, and a water spray pipe. It uses the water pump as power to suck water from the bottom hole of the ship, discharge the water from the rear of the ship through the side pipe, and rely on the reaction force of the water to propel the ship. Its mechanical parts are installed inside the ship and are well protected. The direction of the nozzle is variable, which facilitates ship maneuvering. However, the diameter of the nozzle is limited, and the efficiency of the pipeline and water pump is not high, so the efficiency of the entire system is low. Moreover, because the water in the water pump and nozzle increases the weight of the ship, it is rarely used in general speedboats.
Advantages of water jet propulsion: excellent maneuverability and maneuverability, high propulsion efficiency at high speeds, the main engine is not easily overloaded, and is suitable for shallow water navigation. It is generally used in high-speed and high-performance ships, and is gradually being used in Large and medium-sized ships.
Propeller: A propeller composed of a propeller hub and a number of blades fixed radially on the hub, commonly known as blades. The propeller is installed below the waterline at the stern of the ship. It obtains power from the main engine (see ship power plant) and rotates. It pushes water behind the ship and uses the reaction force of the water to push the ship forward. The propeller is simple in construction, lightweight and efficient, and is protected below the waterline. Propellers are the main propulsion tools of modern ships, and most ships are now propelled by propellers.
However, ships tend to become larger, and after using high-power main engines, problems such as stern vibration, structural damage, noise, and erosion caused by propeller excitation. The fundamental reason for propeller vibration is that the propeller blades are heavily loaded, and local unstable cavitation is easily generated when working in the uneven wake behind the ship, resulting in constant changes in the pressure, amplitude and phase of the propeller acting on the hull.