Straddle Carrier (SC's), Rubber Tired Gantry (RTG) cranes, and Rail Mounted Gantry (RMG) cranes (in the order just presented) can respectively handle a higher throughput with more efficient use of land, but for a steadily rising purchase price and less and less flexibility once they have been installed.
Major vendors of stacking cranes include:
Straddle carriers can move containers either directly from the quay crane to road and rail transport, or simply provide horizontal transport between the quay and the storage yard.
- they are the cheapest to buy
- the most flexible
- put the least weight on the terminal surface
- can run on asphalt
- can only stack 3-4 containers high
- need the most space for maneuvering
- are typically manually operated but can be automated
- are usually diesel powered
- limit yard density to 500 (2 high) - 750 (3 high) TEU per hectare
- typical life expectancy 10 years
Rubber Tired Gantry (RTG)
Gantry cranes are used primarily in the storage area. They are combined with other equipment which performs horizontal transport between the quay and the yard.
RTGs can stack containers much more densely. Most of the world's RTG fleet is capable of straddling at least six containers plus a truck or rail lane down one side.
- they are costlier to buy
- are less flexible but still more flexible than RMG's
- require concrete paving
- still lighter than RMG's thus more suitable than RMG's for terminals built on reclaimed land
- typical height is 1+5 (up to 1+7) and span 6+1 (up to 9+1)
- are traditionally manually operated but automated models exist
- harder to automate than RMG's
- when automated are known as an ARTG
- are traditionally diesel powered but more and more electric systems are being deployed
- support yard density of 1000 TEU per hectare
- typical life expectancy 15 years
Rail Mounted Gantry (RMG)
RMGs run on fixed tracks and can provide the best combination of storage and speed.
- they are the most expensive to buy
- the least flexible
- put the most weight on the terminal surface
- more expensive to install due to the ground works for concrete piles and tracks are needed
- more durable and reliable than RTGs
- stack higher and wider than RTG's, up to 1+7 high and span 20+1 wide
- are typically manually operated but now commonly automated
- easier to automate than RTG's
- when automated are known as an ASC (Automated Stacking Crane)
- are usually electric
- support yard density beyond 1000 TEU per hectare
- typical life expectancy 20 years