Section 9-309 - Construction of power boats; exception; "power boats" defined(a) All tugboats using the Potomac River at the place or places where the same is spanned by the 2 certain bridges in said act provided for, namely the Railway Bridge and the Highway Bridge, are required to equip and fit, not later than July 1, 1909, all smokestacks thereof or other vertical projections with hinges or other mechanical device so as to permit the same to be lowered to the level of the top of the pilothouse of such boats; provided, that all such tugboats the pilothouse of which will not pass under such bridges may be exempted from the operations of the provisions hereof, upon application made to the Secretary of the Army and his approval thereof; provided further, that all tugboats after March 4, 1909, built or purchased, or not on said date actually engaged in business on the Potomac River at the places aforesaid, must have their dimensions approved by the Secretary of the Army before being permitted to use and operate the same on the Potomac River at the places above mentioned: And provided further, that the provisions hereof shall not apply to such tugboats as may, by reason of their structure, be able to pass under said 2 bridges, respectively, without the necessity of operating the draws thereof.(b) The provisions of this section are applicable to "power boats," meaning any boat, vessel, or craft propelled by machinery, whether the machinery be only principal or auxiliary power of propulsion.Mar. 4, 1909, 35 Stat. 1066, ch. 315; Mar. 4, 1915, 38 Stat. 1053, ch. 142, § 6.