A semi-trailer designed for transporting watercraft that includes a gooseneck-shaped cargo platform comprising a front platform, as well as a cargo section and a rear platform located on both sides of the central beam, having at least two axles supporting road wheels, equipped with an air system, articulated to the tractor, characterised in that the front platform (2), cargo section (3) and rear platform (4) that comprise the cargo platform (1) are equipped with at least one pair of pass-through mounting holes (5) and, with respect to the transverse axis (A), the outer mounting hole (5a) is positioned at a right angle (β) and the inner mounting hole (5b) is inclined at an acute angle (α), wherein each mounting hole (5) is equipped with a pair of pass-through locking slots (6a) located below the level of the cargo platform (1), while at the same time each mounting hole (5) acts as a seat for a slide-in installation of the supporting column (7) whose lower part is equipped with at least one pair of pass-through locking slots (6b), and whose upper part is equipped with an installation inlet (8) that is the location for a threaded bracket (9) equipped with a positioning screw (10), to which a supporting crossbar (11) is fixed that contains at least one mounting projection (12), which articulates, by means of a pin (13), to a profile (14) connected by fastenings (16) to a swinging support foot (15), while at the same time the cargo section (2) is connected to the rear platform (4) by an inclined wall (17) under which a compressed air container (18) is located.