Sustainable Marine Structures

Reliable island-scale wave-energy appraisal requires joint assessment of resource magnitude, spectral shape, directionality, persistence, and technology relevance. This study combines hourly Delft3D-WAVE/Simulating WAves Nearshore (SWAN) bulk outputs for 1995–2023 with native frequency–direction spectra for 2024–2025 at Phu Quy and Con Dao. The parent regional model was evaluated against hourly observations; significant-wave-height skill was strongest at Ca Mau (bias = 0.05 m, Root Mean Square Error (RMSE) = 0.09 m, Scatter Index (SI) = 0.24, R = 0.90), while mixed period skill remains a limitation. Year-held-out validation of the seasonal Tp–Te transfer yielded Te RMSE of 0.411–0.453 s at Phu Quy and 0.39–0.42 s at Con Dao, with annual available incident energy (AAE) errors from −1.30% to +1.15%. Excluding 2016 (91.5% coverage) left 28 valid years. Mean transferred incident flux and annual available incident energy were 11.7 kW m−1 and 102.9 MWh m−1 yr−1 at Phu Quy, versus 5.1 kW m−1 and 44.5 MWh m−1 yr−1 at Con Dao. Trend-free prewhitening indicated a positive Phu Quy AAE trend (p = 0.005), whereas Con Dao was not significant (p = 0.07); these model-derived proxies are not observed climate trends. The northeast monsoon supplied 78.0% and 82.5% of directly integrated spectral energy, respectively. At both sites, the dominant energy cell was Hm0 = 3–4 m and Te = 6–7 s, and about 70% of energy fell within a reciprocal ±30° axial window. Attenuator and terminator/overtopping archetypes achieved the highest central resource-shape scores, but overlapping Monte Carlo rank probabilities prevented unequivocal ranking.