Abstract: An appliance for plugging a hole in a boat hull comprises a threaded stem (3), a tubular slide (4) sleeved upon the stem (3), a hub (5) fixed to a distal end of the stem (3), a proximal abutment flange (6) on the slide (4), a distal abutment flange (7) having a converging distal surface on the slide (4), a collar (8) slideable along the slide (4) between the abutment flanges, a plurality of ribs (10), each pivoted at one end to the collar (8) and able to radiate therefrom in the manner of wheel spokes, a like plurality of control arms (11) respectively pivoted at one end to the ribs (10) at a position intermediate the rib ends and pivoted at their other ends to the hub (5), and an impervious membrane (12) secured to the ribs (10) and filling the spaces therebetween when the ribs are radiating from the collar (8). Having been thrust through a hole in a boat hull the slide (4) may be moved outwardly to cause the ribs (10) to swing out and the membrane (12) to cover the hole.