Gantry Cranes

Although cranes existed in ships from the beginning of the 20th century, it was not until the late 1960s that more vessels started to operate with them. At the beginning, cranes were expensive compared with derricks, slower to operate, capacity and outreach was limited and they required highly skilled drivers. With the increase in the carriage of unitised cargo, the practical value of the cranes’ accurate ‘spotting’ ability became more apparent.  Thus cranes, often having a capacity of 25 to 40 tonnes and sufficient outreach to plumb two holds as well as overside, are now commonly found on ships. Placed between two hatches, the crane can slew around 360o and so can operate two hatches without changing the rig. Certain types of container/ro-ro ships and barge carriers are equipped with travelling – portable gantry cranes which straddle the full width of the ship and move along the weather deck on rails situated outboard of the hatch coamings. Such gantries can only be effectively employed in full form ships with extensive parallel body because the rails on which they run must be parallel with each other. The hoist can be slewed to port and starboard and plumb over any part of the area under the gantry and with the gantry being able to move fore and aft, all of the weather deck can be utilised for stowing cargo.  Once the cargo e.g. a container has been lifted clear of the deck, it is placed on board a trailer and driven off the ship via a ramp. Containers are usually handled by shore terminal equipment but gantry cranes can be seen occasionally either in large ships as an interim measure while port facilities are still being developed or in smaller ships for self-sufficiency when operating to less well equipped ports. Gantries are used on LASH (Lighter Aboard Ship) vessels which are designed to combine large ocean going ‘mother ship’ with craft small enough to reach restricted berths.