Pneumatic boat (1) including two inflatable buoyancy chambers (2) extending at least on either side and kept spaced apart by a rigid bottom and by a rear panel (6), at least one stabilizing flap (15) being secured to the base of the rear panel (6) so as to extend rearwards beyond the latter; the flap (15) is fixed to the base of the rear panel (6) by fixing means (11, 12) capable of allowing the flap to occupy, selectively, a functional position and a nonfunctional position; the flap (15) is dimensioned and shaped such that, in the functional position, it extends, laterally, beyond the lateral edge of the base of the rear panel (6) and such that its lateral edge (16) is engaged under the corresponding inflatable chamber (2) and simply bears freely, vertically upwards, against the latter.