In this blog post, we will look at why propellers are still used as the core propulsion device for ships, through their background, technological evolution, various types, and examples of use.
We are currently living in a global era. With frequent trade between countries, countries around the world are conducting trade based on their own interests. Trade between countries is conducted in various ways, one of the most common being by ship. Compared to other means of trade, ships have the advantage of being able to carry large quantities of cargo at once, but they are slow and take a long time to travel. To overcome these disadvantages, people have invented various propulsion technologies and devices, such as oars and sails, since ships were first used.
The development of propulsion technology changed the history of maritime trade. Early oars and sails brought great advances to maritime trade, but they had limitations in that they were dependent on wind and ocean currents. Then, with the rapid development of propulsion technology and changes in the trade environment in the mid-1800s, the propeller was invented, and it has remained the most widely used propulsion device to this day. The increase in ship propulsion contributed to the expansion of trade, which led to the revitalization of the global economy.
Ships operating around the world vary greatly in size, type, and purpose, so the types of propellers used on these ships are also diverse. In this article, we will introduce the specific background behind the emergence of propeller blades and briefly introduce several types of propeller blades.
The overall background to the emergence of propellers is as follows. Around the 1800s, various factors of technological change in society, culture, and industry were closely related to the development of the shipping industry at that time, and shipbuilding technology also underwent a process of change. Among them, the following are important changes and circumstances that led to the emergence of propellers.
First, around the 1850s, there was a famine in Ireland, political revolutions broke out in Europe, and the western United States was being settled. After the American War of Independence, the United States entered the Chinese market to sell opium and silk, and in the process, trade using sailing ships became prevalent. A sailing ship is a vessel that uses sails and wind power to navigate.
Crossing the Atlantic Ocean by sailing ship took between three and 11 weeks, which meant that it took at least several months for traders to respond to changes in market conditions. In addition, sailing ships operated irregularly, which caused a lot of dissatisfaction among American merchants. One solution to this problem was to attempt regular sailing ship service.
However, sailing ships were very difficult to operate in bad weather, resulting in many cancellations, and in an effort to reduce cancellations, other types of ships were sought. That ship was the steamship. Steamships are ships that use the power of steam engines to move, and compared to sailing ships, which are affected by weather conditions, they can operate more freely, and gradually replaced sailing ships in trade.
Meanwhile, in the early days of steamships, paddle wheels were used as propulsion devices. Paddle wheels are devices that push water backward using blades attached to a wheel shaped like a water wheel, and the ship moves forward using the recoil. However, as time passed and steamships became more widely used, problems with paddle wheels began to emerge. These problems included the need for large engines due to the low speed of rotation and the difficulty of maintenance. As a result, attention began to focus on the development of new propulsion systems, and two types of systems were devised: a water jet propulsion system, which sucked water through a turbine and then ejected it through pipes or nozzles, and a propeller with a spiral shape resembling a twisted seashell.
However, water jet propulsion systems have the disadvantages of low efficiency (the efficiency of a water jet propulsion system is less than 0.5 when the power generated by the engine is 1) and the need for larger ships compared to propellers, so propeller systems came to be used on most ships.
Next, we will look at the types and characteristics of commonly used spiral propellers. First, there is the fixed-pitch propeller. A fixed-pitch propeller is what most people imagine when they think of a propeller attached to a ship. It is one of the most common types of propellers used on small racing boats, most merchant ships, large oil tankers, and other vessels.
The second type of propeller is the variable pitch propeller. As the name suggests, the difference between this propeller and the one mentioned above is that the pitch can be changed. (Pitch refers to the straight-line distance that the reference point moves in the direction of the ship’s travel during one rotation of the propeller, considering one point on the propeller. When turning a screw with a Phillips screwdriver, the vertical distance that the screw enters the object during a 360-degree rotation is the pitch.
The last type of propeller we will introduce is the counter-rotating propeller. The counter-rotating propeller gets its name from the fact that two propellers are mounted back-to-back (in the direction of the ship’s travel) and rotate in opposite directions. Counter-rotating propellers are mainly used on merchant ships, naval vessels, and torpedoes.
The development of propellers has had a major impact not only on the shipping industry but also on marine science research. Marine exploration vessels and research vessels have also become capable of stable and efficient exploration thanks to propellers. This has led to propellers playing an important role in various fields, such as marine ecosystem research, seabed resource exploration, and weather observation. In addition, propeller technology continues to evolve, and various research and development efforts are underway to convert it into an environmentally friendly and efficient energy source.
This article provided a brief overview of propellers, which are the most common type of ship propulsion system. We looked at the historical background of propellers, the main types of propellers, and their characteristics. Although other propulsion devices are constantly being developed, it is difficult to find any that pose a threat to propellers, and propeller technology continues to evolve. Propellers will remain the leading ship propulsion device for the foreseeable future.
