Final answer:
Large container ships represent the slowest but most cost-effective shipping mode for heavy freight, vital for the global economy and trade, capable of transporting substantial cargo across long oceanic distances.
Step-by-step explanation:
The slowest mode of shipping heavy freight, which is usually also the most cost-effective, is by large container ships. These vessels traverse the oceans and are essential in the global economy for transporting massive amounts of cargo. For example, a typical ship operating between Shanghai and Los Angeles can travel 10,400 km and carry 10,000 20-foot equivalent containers, each laden with about 10 tons of cargo, amounting to a full load of approximately 100,000 tons.
This type of shipping is most important for global trade as it allows for the cost-efficient transportation of large quantities of goods across the world. Cargo ships are not only integral to maintaining the flow of trade, but they also influence the patterns and strategies behind commercial trade routes and delivery patterns. Container ships, in particular, tend to make more frequent stops along established routes to load and unload cargo, making them a backbone of international logistics.