Intact Stability and Seakeeping Assessment of a High-Speed Patrol Craft: GZ/GMt Metrics with RAO Responses under IMO A.749(18)/HSC Code

Abstract

This paper presents an integrated intact stability–seakeeping assessment for a high-speed patrol craft that links static GZ/GMt metrics to dynamic Response Amplitude Operators (RAOs). Hydrostatics were generated for Half-Load (free to trim) and Full-Load conditions in seawater SG = 1.025 with free-surface effects modeled via simulate fluid movement. Compliance with IMO A.749(18) and the HSC Code was verified using area-under-GZ, φGZmax​​, and initial GMt​. Frequency-domain seakeeping was performed for V = 0/30/50 kn and headings 0°–180°, yielding heave/roll/pitch RAOs.

Both load cases exceed all IMO/HSC limits with wide margins (e.g., positive stability range ≈ 60°, GZmax​ ≈ 0.68–0.74 m at ≈ 54–56°, GMt​ ≈ 1.29–1.45 m). RAOs show clear speed–heading sensitivities: heave increases with speed, peaking in head seas (0°) at ≈ 10 m/m near 5.4 rad/s; pitch increases with speed, peaking in following seas (180°) at ≈ 10 deg/m near 1.0 rad/s; roll is most critical in beam seas (90°) with ≈ 6.66 deg/m near 0.95 rad/s and generally decreases with speed. Synthesizing static margins with RAO peaks yields a practical operating envelope: at higher speeds, prefer head or slight-quartering headings and avoid prolonged beam-sea exposure near roll resonance to protect crew comfort and mission effectiveness. The workflow and reporting compliance tables + RAO summaries are decision-ready and readily transferable to similar patrol platforms.