Which factor does NOT affect a vessel's GZ curve?

The factor that does not affect a vessel's GZ curve is the initial cargo weight. The GZ curve, or the righting arm curve, is primarily influenced by the vessel's geometry and stability characteristics rather than the amount of cargo loaded on board.

The GZ curve represents the righting arm (GZ) at various angles of heel and is shaped by factors such as the center of gravity (G) position, the metacentric height (GM), and the vessel’s hull form. While the initial cargo weight can impact the overall stability by affecting the center of gravity, it does not directly alter the GZ curve itself.

Residual freeboard plays a critical role in determining the height of the center of buoyancy and the subsequent area under the GZ curve, while the list affects the angle at which the righting arm is measured, ultimately influencing the curve's shape. The GM (metacentric height) directly affects the stability characteristics and the steepness of the GZ curve. Hence, the inertia and distribution of weight caused by the initial cargo do not change the inherent shape of the GZ curve, making it the correct answer in this context.