A ship-to-shore rail mounted gantry crane is a specialised version of the gantry crane in which the horizontal gantry rails and their supporting beam are cantilevered out from between frame uprights spaced to suit the length of a standard freight container, so that the beam supporting the rails projects over a quayside and over the width of an adjacent ship allowing the hoist to lift containers from the quay and move out along the rails to place the containers on the ship. The uprights have wheels which run in tracks allowing the crane to move along the quay to position the containers at any point on the length of the ship.
The first quayside container gantry crane was developed in 1959 by Paceco, Inc.[1] Paceco's name for their line of quayside cranes, "Portainer", has since become something of a genericised trademark, used to refer to any quayside container gantry crane.