When you think of shipping, you probably think of giant boats laden with goods heading to foreign lands. That's not a bad image, but it isn't a complete view of the industry. Three stocks to watch in shipping to get a complete view of the sector are Navios Maritime Holdings (NYSE: NM), Textainer Group Holdings (TGH 0.04%), and Expeditors International of Washington (EXPD -0.56%).

Shipping means big boats
There's no denying that shipping involves giant boats. And that's exactly what Navios owns. It directly controls 63 dry bulk and container ships. However, through its ownership stake in other entities, it has much broader exposure to the shipping space, totaling about 160 vessels. Around 25% of its enterprise value is in dry bulk ships, about 25% is in container ships, 35% is tankers (for example, oil and gas haulers), and the rest is in logistics (we'll talk more about logistics in a bit).

Some of Navios' boats. Source: Navios Maritime Holdings.

Investing in Navios is an easy way to get exposure across the entire industry. That's good because shipping rates are often very volatile. With its fingers in different sectors of the industry, pain felt in one area can be offset by good times in another. That said, one thing to keep in mind with Navios and other ship owners is that big boats are expensive, take a long time to build, and last for many years.

Debt, then, is a key metric to watch because of the cost of new ships. And so is the supply of new ships relative to the current world fleet. Fleet age is another factor to consider, since older ships eventually have to be retired and potentially replaced -- not to mention that newer ships often command higher charter rates. Regulations are also a factor, as increasing safety requirements can make older ships obsolete.

That all sounds like a lot, but because of the time it takes to build a ship, these are slow-moving dynamics that you can get a handle on in advance. And Navios, a broadly diversified player in the industry, can provide you with a one-stop investment option, or at the very least, a quick look into what's going on in the shipping space.

No boats!
You may decide that you don't like boats, and believe it or not, that doesn't mean you can't invest in the shipping industry. For example, Textainer owns intermodal containers, the standardized boxes in which things get shipped. Textainer and its peers lease out these boxes to shipping companies, making them a vital cog in the shipping industry. In some ways, its a financial play, with Textainer using debt and equity to fund the building of containers it then leases out. Like a boat owner, then, debt is an issue to watch.

The container market has recently been under pressure from low steel prices, low interest rates, and, thus, ample container supply. Essentially, just about anyone can get into this commodity market. That, however, isn't always the case. And Textainer is one of the largest players in the industry, so it has a scale advantage over marginal players.

An intermodal container. Source: Textainer Group.

But the really interesting thing about owning containers is the profit margins. During the 2007 to 2009 global recession, shippers watched their margins drop from around 10% to negative 10%. Profit margins for container lessors, however, remained above 40% through the difficult period. So, in some ways, investing in a container owner like Textainer is a safer way to get exposure to the shipping industry.

No physical assets at all?
But if that's even too much for you, you might want to consider a pure-play logistics company like Expeditors International. This company doesn't own any ships or containers. It's a middle man that helps other companies arrange for their products to be shipped around the world. It's an asset-light business that the shipping industry couldn't live without.

One of the cool things about Expeditors is that it has no debt -- and hasn't had any for the last decade. While its business will wax and wane with demand for its services, it's highly unlikely Expeditors International is going to go face insurmountable financial strain. That's not something you can say about Navios or Textainer, which both make extensive use of debt to fund their businesses because of the cost of their ship and container fleets. Expeditors biggest assets are the relationships it's developed over time.

Notably, too, Expeditors has increased its dividend annually for more than a decade. So, for conservative investors looking to get into the shipping industry, this might be the least risky way to go.

Bigger than it looks
At first blush, the shipping industry seems pretty simple -- big boats. But when you look more closely, there are other ways to play the space. If you want to get to basics, you'll like Navios and its boats. Back one step is a container lessor like Textainer. And even further back are the logistics companies, like Expeditors, that help arrange shipping. All have their places in the industry, and all three are worth watching and, perhaps, even owning.