Marine service tool

A marine service tool for replacing the seacock valves of a boat or vessel while in the water includes a tool body 6 with means of direct, or indirect attachment 7 to a seacock valve, a placement tube 10 that can be assembled in sections and can slide through a ring seal 9 to precisely place a deformable bung 13 in the bore of a through hull fitting of a boat when the seacock valve is open while maintaining the flooded tool body sealed against the external water pressure and the means of securing the tube 10 through the tightening of a seal retaining ring 8 and deforming the bung once located, by a tension element 14 and a tensioning part 16, so as to form a secure seal in the fitting to allow for the tool body 6 and its associated sealing components 8,9 to be dismantled in situ and removed, the defective seacock valve extracted and a replacement valve fitted under controlled conditions, in accordance with best pipework connection practice and without time pressures or constraints or any period of uncontrolled water flow through the pipework.