A device for protecting a boat hull has an inflatable element with a deflated state, in which the element can be positioned either inside or outside of the boat hull. When located outside the hull, the inflatable element is operatively connected to an inflation/deflation circuit by a conduit. A translational control device causes the inflatable element to be selectively positioned between a position inside the hull and a position outside the hull. When outside the hull, the inflatable element may be inflated or deflated by the inflation/deflation circuit. A bushing provides a through opening in the hull through which the conduit and deflated element pass. A weighted plug is provided at the end of conduit and is shaped to provide sealing engagement with the bushing.