A. Different navigation environments

Seagoing ships: The marine environment is relatively open, the water depth is large, and the maneuverability requirements for ships are relatively low. One propeller can usually meet the propulsion needs of seagoing ships in the ocean, and can reduce the construction cost and maintenance difficulty of ships. The sea conditions are relatively complex, and factors such as waves and currents have a greater impact on ships. The design of a propeller can make the ship more stable during navigation, reduce mutual interference between propellers, and reduce the difficulty of maneuvering ships in severe sea conditions. The size of seagoing ships is usually large, and a single high-power propeller can provide sufficient propulsion to meet the high-speed navigation needs of ships in the ocean.

Inland river ships: Inland waterways are relatively narrow, and the water flow is relatively complex. Ships need higher maneuverability to cope with obstacles such as narrow waterways, bends and bridges. Two propellers can provide better steering and maneuverability, making ships more flexible in inland rivers. The water level of inland rivers varies greatly, and there are many obstacles such as shoals and reefs. Two propellers can increase the propulsion and maneuverability of the ship so that it can sail safely in different water levels and complex waters. The size of inland ships is relatively small, and two propellers can better distribute the propulsion and reduce the vibration and noise of the ship when sailing at low speed.

B. Different uses and loads

Seagoing ships: Seagoing ships are mainly used for long-distance transportation and marine resource development, etc., usually with large loading capacity and long voyage. One propeller with a high-power main engine can meet the long-distance navigation needs of seagoing ships, and can also reduce the energy consumption and operating costs of ships. The load of seagoing ships is relatively stable, mainly cargo and fuel. The design of one propeller can better adapt to the load changes of seagoing ships and improve the propulsion efficiency of ships.

Inland ships: Inland ships are mainly used for inland cargo transportation, passenger transportation and port operations, etc., and usually need to frequently dock and cross narrow waters. Two propellers can provide better maneuverability and maneuverability, which is convenient for ships to operate in busy inland waterways. The load of inland ships varies greatly, and different types of cargo may be loaded according to different transportation tasks. Two propellers can better adapt to the load changes of inland ships and improve the propulsion performance and stability of ships.

C. Technical and cost considerations

Technical aspects: The design and construction technology of seagoing ships is relatively mature, and the propulsion system of one propeller has been widely used in marine engineering. At the same time, the main engine power of seagoing ships is large, and the propulsion efficiency can be improved by optimizing the design of propellers and the matching of propulsion systems. The technical requirements of inland ships are relatively low, and the design of two propellers is relatively simple, easy to manufacture and maintain. In addition, the main engine power of inland ships is small, and two propellers can better exert the power of the main engine and improve the propulsion performance of ships.

Cost aspects: The construction cost of seagoing ships is high, and the design of one propeller can reduce the equipment cost and construction difficulty of ships. At the same time, the operating cost of seagoing ships is also high, and the propulsion system of one propeller can reduce the energy consumption and maintenance cost of ships. The construction cost of inland ships is relatively low. Although the design of two propellers will increase certain equipment costs, it can improve the maneuverability and safety of ships, thereby reducing the operating risks and costs of ships. In summary, the reason why most seagoing ships have one propeller while inland river vessels have two propellers is the result of the combined effects of many factors such as the sailing environment, ship purpose and load, technology and cost.