The difference observed between the Centre of Gravity (CoG) reported in the 'Additional Weight Summary' and the Centre of Load (CoL) shown in the Seastate Load Case Center Report is not caused by an error in your model. Both values are reported in the global structural coordinate system, and the discrepancy arises from the different calculation logic used by SACS at each stage of the workflow.

The 'Additional Weight Summary' reports the geometric centre of gravity of the defined weight group. This value is computed directly from the distribution of the weight items using a weighted average of their coordinates and represents the true physical centroid of the applied mass.

The 'Seastate Load Case Center Report', however, does not represent this geometric centroid. It reports the centroid of the load after SACS converts the defined weights into load cases, particularly when the ACCEL line is used. During this process, inertia forces are distributed to structural joints based on connectivity and load transfer behaviour, and the reported centre is derived from the resulting force system rather than from the original geometric weight locations.

As a result,

1. The CoG in the Additional Weight Summary represents the physical location of the mass.
2. The CoL in the Load Case Center Report represents the location of the resultant force after load generation.

These values are not expected to match exactly, even though total forces and global moments remain in correct equilibrium.

For engineering interpretation and validation, the governing reference should remain the Seastate Basic and Combined Load Case Summaries relative to Mudline Elevation, as these reproduce the correct global moments used for design checks. The Load Case Center Report should be treated as an informational output describing force redistribution rather than as a primary reference for verifying weight CoG or load application location.