Eagle Bulk Shipping stock is going up -- but what's supporting it? Image source: Getty Images.

What happened

Shares of Eagle Bulk Shipping Inc. (NASDAQ:EGLE) are up sharply in Friday morning trading, rising as high as 31% before falling back to a (still respectable) 23.3% gain as of 11:45 a.m. EST.

So what

With no company-specific news to explain the rise, investors are forced to cast their eyes about, in search of a reason why the stock has suddenly become so popular -- but you needn't look far.

Eagle Bulk is, you see, a shipper of dry bulk cargo -- coal, grain, cement, and so on. As such, its fortunes are tied to the rates that it, and other bulk shippers, can charge for transporting this type of goods. Luckily, on the other side of the Atlantic, there happens to be a readily accessible information source that will tell you these rates: the Baltic Dry Index (BDI).

And right now, the BDI is flashing green, with rates up 6.9% since Donald Trump won the election, and up 22% since late October.

Now what

You may have noticed I didn't tell you the exact value of the BDI. (It's actually 974 "points"). The reason for this is that the number doesn't seem to mean much, except as an indication of where rates stand relative to where they stood when the BDI was first published (as the Baltic Freight Index) on Jan. 4, 1985.

Back then, the BDI was given an arbitrary valuation of 1,000 points. Thus, numbers greater than 1,000 (such as the 11,793-point high hit on May 20, 2008) indicate that dry shipping is a really profitable business. Conversely, numbers lower than 1,000 (such as the all-time low of 290 points hit on Feb. 10, 2016) indicate the business is downright lousy.

Right now, the BDI's score of 974 points shows that the shipping business is starting to get back to normal. That's great news for Eagle Bulk Shipping investors, and probably the reason why Eagle Bulk Shipping stock is doing so well today.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.