A remotely operable vessel cover assembly used with a vessel. The cover assembly has a mounting rim secured to the vessel surrounding a circular opening and a circular cover to fit against the mounting rim. A force ring having a plurality of openings is attached to the cover. Connector pins are attached to and extend from the mounting rim and through a plurality of holes in the cover and the force ring. A lock ring is rotatably attached to the force ring and locks the extending heads of the connector pins to the force ring to restrain the cover in an initial position. A force actuator, disposed between the force ring and the cover, expands under fluid pressure to react against the cover forcing the cover against the mounting rim. Upper and lower ramps are connected to the periphery of the cover and a ramp ring respectively. The ramp ring, rotatably supported between the force ring and the cover, has lower ramps positioned to match upper ramps on the cover. The rotation of the ramp ring relative to the cover holds the cover against the mounting rim. A safety lock assembly is connected to the ramp ring to prevent unintended releasing rotation of said ramp ring relative to the cover.