Additional resistance induced by shallow water effects is a critical factor influencing fuel economy during ship design and operation, especially in shallow sea areas such as the Baltic Sea. To address fuel efficiency challenges in such regions, this paper proposes a speed optimization model that accounts for shallow water resistance. The model adopts a multi-objective genetic algorithm integrated with a hypervolume indicator to optimize both total fuel consumption and voyage time. Three operational strategies are investigated: minimizing overall fuel consumption, applying shallow water resistance constraints, and maintaining constant optimal engine power. The effectiveness of each strategy is assessed on a typical Baltic route. Results show that the proposed optimization strategy can reduce fuel consumption by approximately 3.6% without compromising voyage schedules. Moreover, the additional fuel consumption attributed to shallow water effects can be limited to 2.5%. The proposed approach demonstrates strong effectiveness and engineering applicability, providing theoretical support and optimization guidance for green ship design and intelligent speed control.

The experiments of crack propagation at the corner of the porthole structure are reproduced to study the impact of the cracks on the porthole structure of cruise ships by using the finite element software, which verified the feasibility of the current research method. Two types of porthole structure models are then established to discuss the crack propagation characteristics at the corner of the porthole structure under different factors by using the crack propagation software. The ultimate compressive strength of the porthole structure with cracks is also calculated. Finally, the ultimate state function of the porthole structure is proposed based on the improved Paris formula from the viewpoint of fracture mechanics. The failure probability and reliability index of the structure under different conditions are calculated by the Monte Carlo method. The results can provide references for the design of luxury cruise ships.