(a) For purposes of the Transportation Worker Identification Credential requirements of this subchapter, the following vessels subject to this part are in Risk Group A:

(b) Vessels may move from one Risk Group classification to another, based on the cargo they are carrying or handling at any given time. An owner or operator expecting a vessel to move between Risk Groups must explain, in the Vessel Security Plan, the timing of such movements, as well as how the vessel will move between the requirements of the higher and lower Risk Groups, with particular attention to the security measures to be taken moving from a lower Risk Group to a higher Risk Group.