A securing device for securing an object, in particular a vessel mast on a deck of a vessel, comprising: - a coupling ring that can be fixedly attached to or in the deck of the vessel and that is provided with an inner side, as well as - a coupling sleeve that can be fixedly attached to the underside of the vessel mast and that is provided with an outer side, - a blocking device which can block the coupling ring and the coupling sleeve against rotation relative to each other, wherein the coupling ring on the inner side and the coupling sleeve on the outer side are provided with projections and/or recesses which together form a bayonet coupling, and wherein the blocking device comprises: - a blocking element to be fixedly attached to the deck of the vessel, as well as - a blocking body which is blocked against rotation in the coupling sleeve and which is slidable in the axial direction in the coupling sleeve between an upper, releasing position and a lower, blocking position in which the blocking body cooperates with the blocking element such that the blocking body cannot rotate relative to the blocking element, and - a displacement mechanism for displacing the blocking body between the releasing position and the blocking position, characterized in that the displacement mechanism comprises a plug which is screwed into a hole present in the wall of the coupling sleeve, and which is provided with an axially projecting pin which is eccentric to the plug and which is displaceable in a slot present in the blocking body and which extends perpendicular to the axial and radial direction of the blocking body, so that when the plug is rotated, the blocking body is displaced in axial direction. - a coupling ring that can be fixedly attached to or in the deck of the vessel and that is provided with an inner side, as well as - a coupling sleeve that can be fixedly attached to the underside of the vessel mast and that is provided with an outer side, - a blocking device which can block the coupling ring and the coupling sleeve against rotation relative to each other, wherein the coupling ring on the inner side and the coupling sleeve on the outer side are provided with projections and/or recesses which together form a bayonet coupling, and wherein the blocking device comprises: - a blocking element to be fixedly attached to the deck of the vessel, as well as - a blocking body which is blocked against rotation in the coupling sleeve and which is slidable in the axial direction in the coupling sleeve between an upper, releasing position and a lower, blocking position in which the blocking body cooperates with the blocking element such that the blocking body cannot rotate relative to the blocking element, and - a displacement mechanism for displacing the blocking body between the releasing position and the blocking position, - a blocking element to be fixedly attached to the deck of the vessel, as well as - a blocking body which is blocked against rotation in the coupling sleeve and which is slidable in the axial direction in the coupling sleeve between an upper, releasing position and a lower, blocking position in which the blocking body cooperates with the blocking element such that the blocking body cannot rotate relative to the blocking element, and - a displacement mechanism for displacing the blocking body between the releasing position and the blocking position, characterized in that the displacement mechanism comprises a plug which is screwed into a hole present in the wall of the coupling sleeve, and which is provided with an axially projecting pin which is eccentric to the plug and which is displaceable in a slot present in the blocking body and which extends perpendicular to the axial and radial direction of the blocking body, so that when the plug is rotated, the blocking body is displaced in axial direction.