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In December 2015, the 399.2-metre-long CMA CGM Benjamin Franklin [pictured], an Explorer-class container ship, arrived at the port of Los Angeles to general celebration.

She was the largest cargo ship ever to dock at a U.S. port. A few weeks ago she quietly made her last U.S. entry - there is simply not enough capacity to warrant her being on the route.

She is unlikely to be the last ship to find she is too big for today's market.

The new generation of megaships now floating off the order books and onto the shipping routes are the results of the era of high fuel prices between 2004 and 2014 and the low interest rates that followed the financial crisis in 2008. They were specifically designed to operate most efficiently at slower speeds to take advantage of slow steaming economies. In fact some carriers are so large they cannot operate at higher speeds.

Yet, a study last year by the Organization for Economic Cooperation and Development found that around 60 percent of cost savings now comes from engine technologies. Building smaller vessels with better engines would offer more savings than building bigger, slower vessels.

"Cost savings are decreasing as ships become bigger," the OECD said "A large share of the cost savings were achieved by ship upsizing to 5,000 TEU, which more than halved the unit costs per TEU, but the cost savings beyond that capacity are much smaller."

Then there is collapse in global trade volumes following the financial crisis. This year, 18 percent of the world's container ships are anchored and idle. In the last quarter, global shipping capacity increased by 7 percent while demand grew by only 1 percent. As a result, the price of shipping a container fell by nearly half and the once unimpeachable logic of exploiting the economies of scale turned out to be false.

Whilst the shipping lines are considering the numbers to work out if the mega-ships make economic sense the insurance companies are very clear that bigger ships mean bigger risks and are reacting accordingly.

"With a 19,000-TEU [20-foot-equivalent unit] vessel, we're looking at a potential $1 billion loss, if a ship is lost 80 percent laden," said Capt. Andrew Kinsey, senior marine risk consultant, Allianz Global Corporate & Speciality and a former ship's master, at the 16th Trans Pacific Maritime Conference in California in February 2016.

That $1 billion loss would far outstrip the $300 million to $400 million in claims that followed the sinking of the 8,000-TEU container ship MOL Comfort in 2013.

"We'd have to rewrite the law of general average" if one of the new mega-ships was lost, Kinsey said, referring to rules that determine how cargo losses are divided among claimants.

However, the biggest costs associated with the mega ships are on land, at the ports that will have to accommodate them. New cranes, taller bridges, environmentally risky dredging, and even wholesale reconfiguration of container yards are just some of the costly repercussion of berthing a mega ship. In recent years, mega-vessels have caused traffic jams in the water and on-shore as ports struggle to offload thousands of containers. The expense in worker overtime and cargo delays adds up.

To make matters worse, the bigger ships make fewer port visits, leaving operators wondering if they should invest in costly infrastructure improvements for what would amount to infrequent visits.

If the running costs and upfront expense of the mega ships weren't concerning enough, the Organization for Economic Cooperation and Development estimates that whilst world trade will continue expanding in the next few decades it will be at a much slower pace. Given the mega ships already on order the way forward for ship owners may be to pursue a policy of mergers and consolidation if they are to keep their giant ships sailing.