Megaships worsen overcapacity in the container market.
Megaships, which can be up to 400 meters long, seem to be here to stay, not least because so many more are already on order, the product of high fuel costs and low interest rates.
But the trend towards larger vessels is not without problems especially for other businesses in the transport system and the trend could be nearing its limit as the economies of scale associated with megaships decline.
Container shipping capacity has doubled every seven years since the turn of the millennium and will reach nearly 20 million twenty-foot equivalent units (TEU) in 2015 up from 5 million TEUs in 2000.
But since the financial crisis, container capacity has continued to grow rapidly, even as the growth in freight volumes has slowed, creating a massive overhang in shipping capacity and pressuring freight rates.
Capacity growth is being driven by the trend towards larger vessels. The size of container ships has been growing faster than for any other ship type according to the OECD's International Transport Forum.
Between 1996 and 2015, the average carrying capacity of container ships increased 90 percent, compared with a 55 percent increase for dry bulk carriers and 21 percent for tankers ("The impact of megaships" 2015).
The growth in container ship size has been accelerating. It took 30 years for the average container ship size to reach 1,500 TEU but just one decade to double from 1,500 to 3,000 TEU.
Between 2001 and 2008, the average size of newly built ships hovered around 3,400 TEU but then jumped to 5,800 TEU between 2009 and 2013, and hit 8,000 TEU in 2015.
Both the average size of new container ships and the maximum size is set to continue growing over the next five years.
Shipping lines have already taken ownership of 20 megaships with a capacity of more than 18,000 TEU each and another 52 are on order, according to the OECD.
The largest ship so far delivered has a capacity of 19,200 TEU, but carriers with capacity up to 21,100 have been ordered and will be in service by 2017.
Megaships are being introduced into service between the Far East and North Europe, the world's largest route by volume, where potential economies of scale are greatest, but are having a cascade effect on other routes.
Large ships that formerly plied the Far East-North Europe route are being displaced into Trans-Pacific service, and former Trans-Pacific carriers are moving to the Trans-Atlantic route.
The new generation of ultra-efficient megaships is credited with cutting the cost of shipping even further and lowering greenhouse gas emissions.
But researchers for the OECD question whether megaships are contributing to unsustainable overcapacity and imposing unintended costs on shippers, port operators, freight forwarders, logistics firms and insurers.
The new generation of megaships is the lagged effect of the era of high oil prices between 2004 and 2014 and low interest rates since the financial crisis in 2008.
Costs in the shipping industry can be divided into the capital costs associated with the construction of new vessels, operating costs, and voyaging costs primarily related to fuel consumption.
Construction costs increase more slowly than ship size. Increasing a container ship from 16,000 TEU to 19,000 TEU cuts the annual capital cost per TEU-slot by around $69 according to the OECD.
Larger ships are slightly more operationally efficient than smaller ones, with an annual saving of perhaps $50 per slot on a 19,000 TEU ship compared with a 16,000 TEU vessel.