What's the difference between a dock crane and a crane?

There are actually many kinds of cranes and cranes on the dock. There are fixed cranes to unload materials and goods from the ship, or to put goods on board, with a large tonnage;

Crane is mainly mobile, or self-propelled, more flexible and convenient, mainly put the goods on the dock, or from the dock on the truck. Crane gantry wheel type container crane and container front crane, the former is mainly loading and unloading, or mainly heap high.