A motorboat may not be required to be numbered under this chapter if it is:
1. Already covered by a number, in full force and effect, awarded it pursuant to federal law or a federally approved numbering system of another state, provided such motorboat has not been within this state for more than ninety consecutive days.
2. A motorboat from a foreign country temporarily using the waters of this state.
3. A motorboat owned by the United States, a state, or a subdivision thereof.
4. A ship's lifeboat.
5. A motorboat belonging to a class of boats exempted from numbering by the department after said agency has found that the numbering of motorboats of such class will not materially aid in their identification; and, if an agency of the federal government has a numbering system applicable to the class of motorboats to which
the motorboat in question belongs, after the department has further found that the motorboat would also be exempt from numbering if it were subject to the federal law.