The mathematical models of the marine riser lowering blowout preventer (BOP) and the drill string lowering subsea Xmas tree are studied based on new type of cylinder hoisting system, in order to explore the feasibility of accurate operation and the performance of the auxiliary underwater equipment with drilling string compensation function. A simulation model of a cylinder hoisting system under the subsea installation condition is built on the AMESim platform. The subsea installation is simulated when the active drill string compensation is opened and closed under the class 4 sea condition. The maximum safe operation height of a single lifting and lowering operation is analyzed to discuss the impact of different sea conditions on the subsea installation. The results show that the cylinder hoisting system greatly improve the safety of the subsea installation due to its own active compensation function, and the sea condition has a great influence on the operation window and limit operation height. The research results can provide certain theoretical guidance for the national engineering implementation and the field application of the cylinder hoisting system.

With the increasingly stringent requirements of marine environmental protection, all major classification societies have proposed their own environmental protection class notations. Among them, the additional class notation of DNVGL CLEAN（DESIGN）additional notation sets requirements for the design, operation and equipment of ships to reduce the ship's environmental impact from air emissions, sea discharges and hazardous materials from ship to shore. The environmental notation CLEAN（DESIGN）is quite stringent in the DNVGL rules, which is rarely used in the design of container vessels in recent years. A dual-fuel container vessel is a green ship that has the notation CLEAN（DESIGN）. In the process of research and development, the container vessel has broken through a series of design essentials, such as the arrangement of engine room and liquid tanks, sewage treatment and fuel tank protection, reaching a new level of green environmental protection for container vessels. This article systematically summarizes the requirements of CLEAN（DESIGN）notation for the machinery design of container vessels, and studies the influence of this notation on the machinery design of container vessels. It also shows the design ideas and schemes of this vessel combining with the practical project, and presents measures for further improvement of the environmental protection level of container vessels.

The increasing popularity of polar shipping routes poses greater challenge to the marine cold protection technology. Considering the importance of the cold-proof design of the sea chest, the key requirements of the sea chest in the ice region in the relevant specifications of the classification society are introduced in order to ensure the stable operation of the ship in polar environment. The current cold protection technologies are classified and analyzed from the structural design, structural layout and auxiliary deicing according to the principles of different cold protection technologies. The application of the cold protection measures based on different technical principles in different design schemes are highlighted by comparing the characteristics of four cold protection design schemes. The unique technical key points of the cold protection design of the sea chest in the ice region are summarized. It can provide ideas for promoting the scientificity and rationality of the cold protection technology of the sea chest in the ice region in subsequent researches.