The more stuff being made and sold, the higher the demand for such ships, and thus the higher the price to rent one. And vice versa.

This is definitely one of the vice versa times. After rising to robust levels in mid-2018 the Baltic Dry Index has since plunged by about two-thirds.

Here's a brief article on the subject from today's Wall Street Journal:

Free-Falling Freight Rates Spell Trouble For Shipping

Dry bulk shipowners face a long period of uncertainty as spot prices collapse and China shipments shrink.

A slowing global economy, coupled with weak demand from China over the Lunar New Year and from Brazil after Vale SA's iron ore disaster, is dragging shipping rates to near record lows, and few in the industry expect things to improve any time soon.

Brokers in Singapore and London said capesize vessels, the largest ships that move bulk commodities like iron ore, coal and aluminum, were chartered in the spot market for as low as $8,200 a day on Thursday, a $500 decline from Wednesday. Break-even costs for carriers can be as high as $15,000 a day, and daily rates in the capesize market hovered above $20,000 last year.

"Everyone is looking for a catalyst to push the market up, but it's not there," said a Singapore broker.