Propeller is a propulsion device used in Marine vehicles. It has a simple structure and low cost. After nearly a hundred years of development, it has become very mature. In the history of ship development, there have been many different thrusters, some of which are popular, some of which are still being tested, and some of which are active in special fields. Up to now, there are only three mainstream thrusters left, namely propeller, water jet propulsion and pump propulsion. The development history of water-jet propulsion is not much shorter than that of propeller. As early as when water pump was invented, people thought whether it could be used to propel ships. Now, it has been used in many fields of high speed.
The principle of water-jet propulsion is different from that of propeller. In addition to the recoil force generated by pushing water, propeller is subject to some Bernoulli force just like the wing, while water-jet propulsion is purely dependent on the recoil force when water is ejected. Water jet propulsion has high speed maneuverability and is more efficient when the speed is greater than 20KM/H. However, its overall efficiency is low and its structure is complex and huge. The pump used in submarines is a branch of water-jet propulsion, which is more efficient than propellers and has a lower noise level than propellers due to duct shielding, making it suitable for use on submarines.
Shaveless pump push is a development trend of submarine pump push. Its motor stator is installed in the duct and the stator drives the rotor directly. Unlike ordinary pump push, which needs to draw out a shaft, the noise is lower and valuable internal space can be saved. But it is complex, heavy, difficult to build and maintain, and suitable only for use in areas such as military submarines where costs are not considered. Is there a propulsion system that combines high efficiency, low noise and simple structure? Yes, it's magnetorheological propulsion. It USES electromagnetic action to drive seawater to get thrust, theoretical efficiency is very high, and there are no moving parts, very low noise. But it is still hampered by low actual efficiency and will not be able to leave the laboratory for some time. But if you can do that, it's going to be the direction of the future thrusters.