Measuring ship squat, trim, and under-keel clearance using on-the-fly kinematic GPS vertical solutions

Knowing the effects of squat on large ships traveling in confined channels is of great concern to shipping operators. Defined as supplementary sinkage of a ship relative to the water level and caused by the ship's movements, squat is a significant component of the under-keel clearance (UKC) allowance and is critical for maritime safety. A trial was conducted using an on-the-fly (OTF) kinematic GPS positioning technique to measure the squat, trim, and UKC of the large passenger ship Crystal Symphony while it was transiting the Cairns Channel. This exercise was rather successful. The paper presents the trial procedures and results. The results include sinkage, trim, and UKC measurements for both inward and outward runs. The squat measurements also show a high degree of agreement with the squat predictions based on an empirical formula. OTF kinematic positioning is therefore determined to be a new efficient technique for directly measuring ship squat