An inflatable boat comprising: an inflatable float that is U-shaped and open at the stern, and that braced by a transom; a floor that is disposed inside the space defined by the float, and a V-shaped keel formed of a flexible canvas sheet fastened to the float and to the transom and tensioned by a longitudinal inflatable keel-forming spacer interposed between the floor and the canvas sheet; the inflatable keel-forming spacer is formed by at least two elongate and flat chambers inflated under a relatively high pressure; and the two chambers have their respective bottom longitudinal edges touching and their respective top longitudinal edges spaced apart from each other so that the keel-forming spacer is generally V-shaped in cross-section.