I spoke to the jurilinguist at the office. The word “bâtiment” is defined in section 2 of the act. It's the equivalent of “vessel” in English. The definition is as follows:
“vessel” means a boat, ship or craft designed, used or capable of being used solely or partly for navigation in, on, through or immediately above water, without regard to method or lack of propulsion, and includes such a vessel that is under construction. It does not include a floating object of a prescribed class.
The jurilinguist also mentioned that the terms “bâtiment”, “navire” and “vessel” are all terms that have been standardized in this field by the naval standardization committee. Other acts also use the same terms.