The Panama Canal is being expanded to handle “New Panamax” containerships with 19 containers across the deck. Shipping lines are ordering 18,000 TEU jumbo ships, sometimes called “Ultra Large Container Ships” (ULCS) with 23 containers across the deck (Jumbo-23). Many existing quay cranes are not capable of servicing these larger ships. The choice is either to purchase new larger cranes, or enlarge existing cranes.
This article discusses enlarging existing cranes: how much, enlarging methods, conceptual cost and schedule estimates, and other considerations. Even some recently purchased cranes would require enlarging. Figure 1 presents the outreach demand of Panamax, New Panamax, and Jumbo-23 cranes, and the lift height and outreach of some recently purchased cranes.
In many cases, cranes can be modified for less cost and in less time than procuring a new crane. The cost of a new crane ranges from US$8–10 million. Enlarging and upgrading costs vary from 25% to 60% of the cost of a new crane, and the time required to enlarge a crane is sometimes half that of procuring a new crane. Wheel loads for larger cranes may exceed the stated allowable wheel loads. Often, this is not a problem since increased capacity can usually be justified using modern analysis methods and considering the as-built crane girders.
Ship sizes: Panamax, New Panamax, and Jumbo-23
Increasing lift height and outreach
Larger ship sizes demand more crane lift height and outreach. There are many ways to enlarge a crane. Figure 2 presents issues and examples of modifications required for a typical 17-wide post-Panamax crane to service a 19-wide New Panamax ship.Increase lift height Increasing the lift height is a common modification. Often, new leg sections are inserted. Diagonal braces may be added to the portal frame to maintain the crane stiffness in the trolley travel direction. Small diagonal braces may be added at the top of the landside and waterside O-frames to maintain stiffness in the gantry travel, and for strengthening. In areas of high seismicity, the seismic performance of the crane should be evaluated. It is practical to strengthen or provide ductile details for adequate seismic performance.
Many contractors have specialized jacking systems that can raise a crane in one day. Additional time is required for preparation, fabrication of inserts, and modification of non-structural elements such as the elevator, electrical components, stairs and platforms, and for other structural modifications such as stiffening the portal frame. Specialized jacking frames rest on the sill beam of the crane and maintain a load path through the crane’s wheels onto the wharf.
The cost to raise a crane varies, however a standard raise is around $1 million including associated modifications.
Increase outreach
Recently, many owners have purchased container cranes that can service ships with 22 containers across, “22-wide ships.” The outreach may be a little too short for the larger Jumbo-23 ships. Usually little effort is required to increase the outreach by one container. For increases up to about two meters, it is often practical to make modifications to the trolley, trolley runway, stops, bumpers, the platform at the boom tip, and runway support structures.
For larger increases, more significant modifications are required. Outreach is often increased by removing the end of the boom, modifying it on the quay, and reinstalling it on the boom tip. Sometimes it is necessary to remove the entire boom and modify it on the quay. Other structural modifications may include replacing the forestays with stronger stays and strengthening the upper diagonal and apex structure.
The boom hoist capacity may not be capable of lifting a heavier boom. Sheaves are often added to the existing hoist system without changing the motor or the drum. The increased length of hoist rope is often double-wrapped on the existing drum. To avoid double wrapping, the boom may be stowed in a partially raised position. Unlike the boom hoist drum, it is not practical to double-wrap the main hoist or the trolley tow ropes. If the existing drum grooves cannot accommodate the increased rope length, the dead wraps can be moved to the ungrooved portion of the drum. If there is no room for the additional rope, a new drum would be required.
The cost to increase the outreach varies. If only localized modifications are required, the cost can be less than $200,000. If major structural and mechanical modifications are required, the cost can be $1 million–$1.5 million.
To read the full article download PDF
