SOUTH CHINA SEA (CNN) -- Aboard the Svend Maersk, the sound of the ship's five-story high engine permeates like a heartbeat through the four-football field length of ship.
Chief Officer Christian Vium talks to CNN's Eunice Yoon as night falls on the bridge of the Svend.
It's also the heartbeat of the world economy, as the Maersk takes its thousands of containers filled with shoes, computers, furniture and fireworks from China to markets in Europe.
But a more telling sight is when the massive vessel nears Singapore and passes by dozens of idle ships.
"A lot of ships have been taken out of service or laid up. Instead of sailing with half empty ships, it's cheaper to lay up the ship," said Bo Nikolaisen, captain of the Svend. "I feel lucky, of course, that I am on a ship that is still working."
A 10 percent drop is expected this year in the shipping business, which one analyst called "a $20 billion black hole." It's an industry that is a prime indicator of the global economy -- 90 percent of world trade is carried on ships such as the Svend Maersk to ports and onto shops around the world.
CNN sailed with the crew of the Svend Maersk for four days as the ship sailed from Hong Kong to Malaysia to get a sea-level view of the industry. What stands out on these vessels is the incredible size -- the vessels stack 15 stories high -- and streamlined crew: Only 21 men are required to run the ship.
The crew comes from Denmark, Germany, Romania and the Philippines. "We've been joking that the ship was the United Nations at sea," said Captain Nikolaisen. "There are many nationalities, sometimes eight, maybe more. They are professionals -- most of them -- and they know that we cannot afford to be unfriendly to one another."
Some of the crew are over 60; among the youngest is 24-year-old recruit Joey Lamasan. Lamasan still has trouble sleeping since he left his village in the Philippines. But here, he can earn triple what he would make back home.
"The salary in the Philippines is too small compared to the salary on board the ship," said Lamasan, who is on a six-month contract -- typical for many young seafarers.
Piracy has been making the news in recent months, exacerbating economic concerns of the financial crisis. More common than large-scale theft of multi-million dollar cargo is thieves coming on board and stealing cash, computers and personal items.
But what they fear the most "would be fire or explosion," said Captain Nikolaisen. "We cannot run away."
Life on the boat -- like the scenery -- can be repetitive. There is no mobile phone service, no booze, and limited Internet access. Many of the seamen work in two four-hour shifts... to stay alert. Meals and coffee breaks are routine. Free time is usually spent alone in the cabins, playing computer games together, or occasionally calling home on a satellite phone.
"Ten to 15 minutes just to hear how it's going and keep contact. Also it's nice for the kids too. So they can still remember what Dad sounds like," Captain Nikolaisen said.
After two months on the high seas officers get two months' vacation. "When I am out here I miss the family," Nikolaisen said. "And when I am at home I miss a little bit being at sea."