Defects such as voids in composite materials often degrade the mechanical properties of laminates. Even if these materials are manufactured based on the design requirements, there is a possibility of instability occurring in these composite structures. In this study, several prototypes were developed based on changes in composite ship design conditions (glass fiber weight fraction and fabric combination type) using a hand lay-up approach. The fabrication quality was quantitatively defined using the burn-off test, and statistical analysis was performed. A combination of chopped strand mat and woven roving material laminates possessed relatively less void content in the entire glass content (G_c) region (30–70 wt%) compared to a chopped strand mat single-material laminate. The effect was more pronounced in the high-G_c region (50–70 wt%) than that in the normal-G_c region (30–50 wt%). The composite hull plate can be designed seamlessly according to changes in fabrication quality. To ensure safety, the thickness of the laminate must be greater than that specified in the ISO standards, regardless of the combination type in the normal-G_c region. As a result of the void content considered, the flexural strength in the single laminate decreased by 15.02%. Furthermore, 3.33% of the flexural strength calculation decreased in the combined laminate compared to that in the ISO rules. Thus, a single CSM material can be designed to be thicker than a combined-material laminate with the same G_c, while considering the void content on the mechanical properties.

Glass fiber-reinforced polymer (GFRP) ship structures have hull plate thicknesses of 10 mm or more and are fabricated using a higher proportion of resin matrix systems than E-glass fiber reinforcements. Therefore, GFRP is classified as a highly attenuative material, and this characteristic is a major cause of large errors in ultrasonic nondestructive testing for quality inspections. In this study, considering the aforementioned design and fabrication characteristics of GFRP ship structures, hull plate prototypes with various glass fiber weight fractions, glass contents (Gc), and laminate thicknesses were fabricated. Then, a pulse-echo ultrasonic test was performed with the fabricated prototypes, and the attenuation characteristics of the GFRP hull plates were investigated by conducting statistical analyses. These results demonstrated that with a variation of 30–50% in the Gc used for GFRP structure design, the plate thickness variation had a greater impact than the Gc variation on the attenuation characteristics. The increase in Gc naturally increased the scattering of ultrasonic waves but did not significantly affect the attenuation coefficient. The effects of the inner voids on the ultrasonic waves were also investigated, and the results confirmed that the laminates in this Gc region did not significantly affect attenuation.

Glass fiber-reinforced polymer (GFRP) ship structures are generally fabricated by hand lay-up; thus, the environmental factors and worker proficiency influence the fabrication process and presence of error in the non-destructive evaluation results. In this study, the ultrasonic testing of GFRP hull plate prototypes was conducted to investigate the statistical significance of the influences of the design parameters, e.g., the glass fiber weight fraction (Gc) and thickness variations, on the measurement error. The GFRP hull plate prototypes were fitted with E-glass fiber chopped strand mats (40 wt % content) with different thicknesses (7.72 mm, 14.63 mm, and 18.24 mm). The errors in the thickness measurements were investigated by conducting pulse-echo ultrasonic A-scan. The thickness variation resulted in increased error. Furthermore, hull plate burn-off tests were conducted to investigate the fabrication qualities. Defects such as voids did not have a significant influence on the results. The statistical analysis of the measurement errors confirmed that the thickness variations resulted in a strong ultrasonic interference between the hull plates, although the hull plates had similar specific gravity values. Therefore, the ultrasonic interference of the layer group interface should be considered to decrease the GFRP hull NDE errors with respect to an increase in the thickness and Gc.

Fast patrol boats account for a large number among the numerous vessels used in naval fleets. Owing to their operational characteristics, which involve relatively high speeds, they contribute to emissions significantly. This study presents an optimized design concept for a diesel–battery hybrid electric propulsion system integrated into the general ship design process for fast patrol boats. The optimization design uses mixed-integer linear programming to determine the most eco-friendly shares ratio of battery and diesel usage while satisfying high-endurance operational scenarios. A shares ratio of 1.259 tons of diesel to 2.88 tons of batteries was identified as the most eco-friendly configuration capable of meeting a 200-nautical-mile operational scenario at a maximum speed of 35 knots for the selected case study. A quantitative comparison through a global warming potential (GWP) analysis was conducted between conventional diesel propulsion systems and the designed diesel–battery hybrid electric propulsion system, using a life-cycle assessment (LCA) standardized under the ISO framework. The analysis confirmed that the optimized hybrid propulsion system can achieve a GWP reduction of approximately 7–9% compared with conventional propulsion systems. Few studies have applied LCA in this field, and the application of batteries as hybrid secondary energy sources is viable and sustainable for high-endurance scenarios.