The utility model provides a single face bedplate subassembly for boats and ships sea chest blast, boats and ships sea chest has seted up a trompil, single face bedplate subassembly includes: a bedplate, the passageway has been seted up to the bedplate, the central line of passageway with the central line coincidence of bedplate, the bottom surface of bedplate be used for to lean on in boats and ships sea chest's top surface with cover in the trompil, a nozzle stub, the one end of nozzle stub wear to establish and connect in in the passageway, the one end of nozzle stub is used for wearing to locate in boats and ships sea chest's the trompil. The utility model discloses a preassemble on the bedplate the nozzle stub, the shipyard need not retreatment the nozzle stub with the weldment work of bedplate, the utility model discloses a wall of trompil with between the bottom surface of bedplate third welding seam edge arrives the outer wall of the one end of nozzle stub with between the bottom surface of bedplate first welding seam edge can remain sufficient clearance distance, has guaranteed the welded fastness.