Malcom McLean revolutionized the seagoing shipping business almost 50 years ago with his invention of the 20-foot shipping container. Before that, cargo wasn’t neatly separated and armies of dockworkers had to sort out goods, warehouse them and load and unload them from ships. McLean’s invention is easily moved by cranes and stored in open-air yards instead of warehouses. While thousands of longshoremen lost their jobs, containers made global shipping cheaper and faster.

Even McLean might not have realized the full import of his invention, though. Helen of Troy’s face may have launched a thousand ships, but McLean’s box launched fleets of ships capable of carrying tens of thousands of containers, and each container can carry everything from two cars to 29 tons of soybeans to 1,400 toasters. And those ships bring in boatloads of cash.

Seaspan is one of the largest owners and managers of containerships, operating a fleet of 89 ships capable of carrying a total of 626,300 such containers. The company has an additional 12 ships on order with deliveries stretching into 2016, adding an additional 25% of capacity, and they won’t be sitting idle on docks—all of them are committed to long-term charters. In October the company took delivery of a new, fuel-efficient, 10,000-container ship known as a SAVER, which had already been chartered to Mitsui OSK Lines for an eight-year term.

While the container business can be volatile, those long-term charters help shield Seaspan (NYSE: SSW) from swinging market rates for charters. Container shipping contracted by 10% in 2009 because of the recession, but the industry grew at an annual rate of better than 10% between 1999 and 2008, thanks to surging global trade. The industry largely rebounded by 2010, with containership demand growing at an annualized 6%.

Owning containerships is an expensive proposition, and more and more shipping companies rely on chartered ships from companies such as Seaspan to meet demand. While only 15% of containerships were chartered in the early 1990s, more than half of the containership fleet is now chartered. For instance, Mitsui OSK Lines is currently in the market for six ultra-large containerships capable of carrying 18,000 containers each. But it will charter them from another company instead, spending between $151 million and $160 million each, and Seaspan is in the running to provide them.

Seaspan shares currently yield 7.2% after a decline of nearly 17% so far this year. As China’s economy has slowed and Europe has slipped into recession, investors are clearly worried that global trade will slow. At the same time, a wave of new containerships is coming into the market, including the ultra-larges, which will pressure the day rates ship owners can charge.

That concern doesn’t apply to Seaspan, though. Virtually every one of its ships is booked solid this year. It won’t face lower day rates for some time, with an average charter of five years remaining on most of its ships. The new ships it expects to take delivery on over the next two years are also already chartered for terms ranging from five to 10 years.

As a result, Seaspan’s $0.35 quarterly dividend should be secure for at least the next few years, thanks to its predictable cash flow and high use rate. As of the end of the third quarter of 2014, 99.2% of the company’s fleet was at sea and expected to generate $6.4 billion over the next seven years. As a result of its stable operations and growing fleet, revenue growth over the past five years was 24.2%, while earnings-per-share growth has been 24.1%.

Earnings this year are expected to come in at $0.88 per share, 4% lower than last year mainly because of an increase in expenses. But with a wave of new deliveries coming next year, earnings are forecast to grow by more than 47%, to $1.30 per share.

Given Seaspan’s strong market position, it should continue to win new charters because it has easier access to capital than many of its competitors do. It is able to quickly begin construction on ships when needed. In the third quarter, it entered into agreements with Maresk Lines to build four new 10,000-container vessels and extended the charters on five others. Another shipping line, Yang Ming, confirmed that Seaspan was chosen to build and manage 15 new vessels for the company on 10-year charters.

Seaspan is uniquely positioned to aggressively expand its fleet as container trade demand is expected to grow by 8% annually over the next few years. Even if the global slowdown were to worsen and earnings growth were to slow, its dividend should be secure given the long-term charters its ships operate on. There are already signs that shipping may be stabilizing: AP Moeller Maresk, the parent company of Maresk Lines, recently announced that it expects full-year earnings to come in at $4.5 billion rather than $4 billion, mainly because of a 6.6% increase in shipping volumes.

With a growing fleet boosting revenue and earnings, Seaspan is a buy up to $27.