((a)) Except as otherwise provided in this section, this chapter applies to any vessel for which the application of an international agreement or other law of the United States to the vessel depends on the vessel’s tonnage.
((b)) This chapter does not apply to the following:
((1)) a vessel of war, unless the government of the country to which the vessel belongs elects to measure the vessel under this chapter.
((2)) a vessel of less than 24 meters (79 feet) overall in length.
((3)) a vessel of United States or Canadian registry or nationality, or a vessel operated under the authority of the United States or Canada, and that is operating only on the Great Lakes, unless the owner requests.
((4)) a vessel of United States registry or nationality, or one operated under the authority of the United States (except a vessel that engages on a foreign voyage) the keel of which was laid or that was at a similar stage of construction before , unless—
((A)) the owner requests; or
((B)) the vessel undergoes a change that the Secretary finds substantially affects the vessel’s gross tonnage.
((5)) a barge of United States registry or nationality, or a barge operated under the authority of the United States (except a barge that engages on a foreign voyage) unless the owner requests.
((c)) An existing vessel that has not undergone a change that the Secretary finds substantially affects the vessel’s gross tonnage (or a vessel to which IMO Resolutions A.494 (XII) of , A.540 (XIII) of , or A.541 (XIII) of , apply) may retain its tonnages existing on , for the application of relevant requirements under international agreements (except the Convention) and other laws of the United States. However, if the vessel undergoes a change substantially affecting its tonnage after , the vessel shall be remeasured under this chapter.
((d)) This chapter does not affect an international agreement to which the United States Government is a party that is not in conflict with the Convention or the application of IMO Resolutions A.494 (XII) of , A.540 (XIII) of , and A.541 (XIII) of .