Disclosed is a floating structure for an autonomous watercraft with a keel deployed and recovered on a vessel. The longitudinally elongate structure includes a floating port-side and starboard lateral edges and a submersible bottom submerged when the structure is in the water, the lateral edges and the bottom defining an interior space at least partly submerged when the floating structure is in the water, the lateral edges defining a prow at the front and, at the rear, an opening towards the rear of the floating structure, which opening is downwardly limited by the submersible bottom with at least one longitudinally elongate slot open towards the rear for the passage of the keel, and the floating structure is configured in order that at least the front portion of the autonomous watercraft including the keel can engage by floating inside the interior space, with the keel engaging in the slot.