What happens if weight is added to the high side of a vessel with a negative GM?

When weight is added to the high side of a vessel that already has a negative GM (metacentric height), it effectively increases the list of the vessel. A negative GM indicates that the vessel has an unstable equilibrium, meaning that any interference from external forces or added weight can exacerbate its list rather than help right it.

In this case, adding weight to the high side moves the center of gravity further away from the centerline, increasing the angle of heel. As the weight shifts the center of gravity upwards and away from the vessel's center of buoyancy, the righting moment is diminished, making it more difficult for the vessel to return to an upright position. Consequently, the vessel is likely to experience an increased angle of list, leading to a more precarious situation.

Thus, adding weight to the high side in this scenario ultimately contributes to an increase in the angle of list, confirming the reasoning behind the chosen answer.