A motorboat or sailboat is not required to be numbered under this part if it is:
(1) covered by a number in effect that has been assigned to it pursuant to federal law or a federally approved numbering system of another state if the motorboat or sailboat has not been within this state for a period in excess of 90 consecutive days. After 90 consecutive days within this state, this state becomes the state of principal use of the motorboat or sailboat and the owner shall apply for a Montana number, certificate of number, and registration decal.
(2) a motorboat or sailboat from a country other than the United States temporarily using the waters of this state;
(3) a motorboat or sailboat whose owner is the United States, a state, or a subdivision of a state; or
(4) a ship's lifeboat.