Art. 59. In none of the contracts shall a longer term than 7 years be granted the contracting party, to count from the date of its signing, so that safe and free passage is given steamers drawing 3 feet in the entire distance of the contract. Art. 60. The improvements in the Rio Branco, shall commence with the destruction and regulating of the Cujubim rapid, so that from now on navigation is assured during the Winter to Villa Boa Vista. Art. 61. The studies, plans, constructions, inspection and direct conservation of these works are under the supervision of the Minister of Transportation; but before the respective contract is signed, copies of the plans and descriptive memorandum referring to the project shall be furnished the Minister of Agriculture, so that he may be heard upon the opportunity and the order in which these works shall be executed, in the interest of the economic development of the region, and that they may be conveniently attended by those casually interested in the colonization and development of the industries along the banks of the rivers, or in commerce in general. In case it is found that the destruction and regulation of the Cujubim rapid cannot be done during one season of low water in the river, the Minister of Agriculture, by agreement with the State of Amazonas, can order to be constructed a Decauville line of the type described in articles 45, second part and 51, in the belt line constructed by that State along waterfalls, so that the leasing and colonization of the national plantations of Rio Branco is no longer delayed. CHAPTER III Complementary measures Art. 62. All vessels of every kind intended for the fluvial navigation in the valley of the Amazon are free of all import duties, including the fees. This exemption shall be given by the custom houses of Belém (Pará) and Manáos, through a requisition to the Minister of Agriculture, which the importer shall have asked for, declaring in his request the number, class and tonnage, the draft and the cost and the purpose of each vessel. Art. 63. The vessel imported under this favor, if sold outside the valley of the Amazon, or even within it, to a foreign country, shall pay the proper duties according to the law of the budget in force in the year of its importation.