I. Types of Ship Propulsion Systems and Their Industrial Structure
Ship propulsion systems, consisting of main engines (diesel engines, steam turbines, gas turbines, etc.), transmission systems (shafting, gearboxes, couplings, clutches, etc.), and propellers (propellers, omni-directional thrusters, side thrusters, etc.), are the most important and essential equipment on board a ship. On average, their value accounts for approximately 35% of the total equipment cost and about 20% of the total ship price. Currently, there are four main propulsion methods for various types of ships worldwide: ① Steam turbine propulsion system - replaced reciprocating steam engines, and then was replaced by diesel engines. It is currently mainly used in LNG (liquefied natural gas) carriers and nuclear-powered military ships. The technological development trend of steam turbines is to continuously enhance reliability and maneuverability, improve controllability, and simplify equipment. ② Diesel engine propulsion system - comprehensively replaced reciprocating steam engines and steam turbines, becoming the main ship power, currently used in various types of ships, as the main equipment of the diesel engine propulsion system. ③ Gas turbine propulsion system - started to be used as the main engine on merchant ships in the 1950s, but has never been widely used, currently mainly used in military ships, as the main equipment of the gas turbine propulsion system. ④ Electric propulsion system - started to be used in the shipbuilding field in the 1990s, currently used in military ships and small merchant ships. The proportion of ships currently using electric propulsion is still relatively small.
Currently, the research and development, and design of ship propulsion systems are still led and monopolized by countries and regions such as Europe, the United States, and Japan. The manufacturing of steam turbines and boilers, gas turbines, and electric propulsion devices is also controlled by companies in these countries. However, the manufacturing of diesel engine propulsion systems, which account for the largest proportion of ship propulsion systems, has basically shifted to South Korea, Japan, and China.
 
II. Significance of Promoting the Application of New Energy Ship Propulsion Systems
Currently, 95% of ship propulsion systems are diesel-powered. However, ship diesel engines have several major drawbacks.
(1) Use of non-renewable energy. The power source is non-renewable fossil fuels. According to scientists' predictions, the earth's current oil reserves will only last for another 60 years. In other words, fossil fuels on Earth will be depleted in 60 years. Therefore, we must use other energy sources, preferably renewable energy. (2) Air pollution. Although current technological advancements have gradually controlled the emission of pollutants from diesel engines, considering that ultra-large ships consume thousands of tons of fossil fuels per voyage, and there are also old diesel engines left over from history, these will emit large amounts of pollutants, causing serious air pollution. This is undoubtedly contrary to the theme of green environmental protection. (3) Serious noise problems. According to relevant data, the noise emitted by diesel engines on ships can reach 120 decibels. This is a very frightening number; long-term exposure to such an environment will severely damage the hearing of personnel. This problem is particularly prominent in smaller ships. Therefore, it is necessary to address this issue. However, due to the structure and working principle of traditional diesel engines, it is difficult to solve the noise problem. Therefore, breakthroughs can only be sought in new energy propulsion systems.
 
Promoting new energy propulsion systems and using sustainable energy to power them, while further reducing harmful gas emissions and addressing noise issues, will not only provide a good working environment for engine room personnel on ships but also reducing pollutant emissions is in line with the country's sustainable development path. Therefore, developing new energy ship propulsion systems has significant development significance.
 
III. Current Application Status and Development Trend of New Energy Ship Propulsion Systems
New energy refers to various forms that directly or indirectly come from the heat energy generated by the sun or the deep interior of the Earth. Compared with traditional energy, new energy has the characteristics of less pollution and large reserves, and is of great significance for solving the current serious environmental pollution and resource depletion problems in the world. As the fuel consumption of ships accounts for an increasing percentage of total fuel consumption year by year, leading to the increasing proportion of fuel in the cost of ship transportation, how to further improve the energy efficiency of ships and effectively reduce transportation costs has become imminent. With the continuous advancement of science and technology, the unique advantages and benefits of new energy, such as wind energy, solar energy, nuclear energy, biomass energy, and tidal energy, in energy saving and emission reduction have become increasingly significant, and their application and promotion in the shipping industry have become a trend.
1. Wind energy. Wind energy comes from the kinetic energy generated by the flow of a large amount of air on the earth's surface. It is a pollution-free and infinitely renewable resource. The history of human use of wind energy can be traced back to ancient times. With the continuous improvement of scientific and technological levels, industrial society has rich experience in the use of wind energy, and supporting industries and infrastructure are relatively mature. However, the use of wind energy has some drawbacks that are difficult to completely eliminate, such as intermittency, high noise levels, susceptibility to terrain influence, and interference with radar signals. Currently, the use of wind energy mainly takes the form of wind power (wind-assisted navigation) and wind power generation. In ships, it is mainly used as the main or auxiliary power for navigation, and wind power generation technology is only used in a few ships.
In fact, as early as the 1980s and 1990s, Japan made new breakthroughs in the research and utilization of wind-assisted navigation. In 1980, Japan built the first oil tanker equipped with ordinary wing sails, the New Aede Maru. The New Aede Maru was equipped with two sails, 12.15 m high and 8 m wide. Later, it built motor sailing cargo ships such as the Senyo Maru and Nissan Maru. In 1984, it designed and built the 2600t Usuki Senpou Maru and another 31000t modern wind-assisted ocean-going cargo ship. On December 15, 2007, the world's first kite-powered cargo ship, the Beluga SkySails, set sail from Hamburg, Germany.
 
2. Solar energy. The utilization of solar energy mainly involves two aspects of technology: photothermal technology and photovoltaic technology. Photothermal technology utilizes the thermal radiation of sunlight, and its most successful application is solar water heaters. A further extension of this technology is solar thermal power generation, which uses collectors to concentrate solar radiation heat energy to heat water to produce steam, and then uses steam turbines and generators to generate electricity. Considering that the demand for hot water during ship operation is not high, thermal power generation...