A tug is a vessel that looks small but has an enormously powerful engine—an engine almost as big as one that moves a cargo ship. In fact, the tugboat’s job is to push and pull cargo and passenger ships around.

Big ships need help getting in and out of the narrow spaces between piers in a harbor. If they used only their own power, they might either smash themselves up or crush the piers. Tugs, working together, can push a little here, pull a little there, and ease a huge vessel gently into place.

A tugboat captain must have a great deal of knowledge about the harbor in which he works. In order to pass his captain’s examination, he has to draw a map of the harbor from memory, showing every pier and marker and even the rocks, hills and valleys underwater. Most important, he must have a feel for what a ship is going to do when he nudges her at a certain point or when he reverses his propeller and pulls.

For all his skill and responsibility, the captain wouldn’t think of wearing a uniform at work. He prefers old work clothes, and he sits down with the crew when the cook serves up jumbo-sized meals.

The cook goes on duty in the galley at any time from one o’clock in the morning on, depending on what time the tug must start work. Breakfast may be at three or four, but the usual time is six. And often the cook’s job isn’t over at four in the afternoon when he serves supper. If the tug is working overtime, he fixes a meal called a “midnight snack” which the men eat perhaps around seven o’clock. There’s enough food in the snack to feed a shoreside person for a whole day.

Besides the captain and the cook, a tug needs a chief engineer, an oiler, a fireman and a deckhand. The deckhand works with the hawsers that are often used when a tug has to pull a big ship.

This is what happens: An AB aboard the ship holds a coil of light line, called a heaving line. At the end of the line is a ball-shaped knot called a monkey fist. The AB gives a big swing and sends the monkey fist and line flying down to the tug. The deckhand on the tug grabs for the line. He’s not an outfielder trying to catch the ball. The monkey fist is there only to make the line uncoil and go straight.

The deckhand pulls on the heaving line, which is attached to a hawser on the ship. (Sailors don’t say the line is attached or tied. They say it’s “bent” to the hawser.) The hawser is so big that it can’t be thrown, but it can be hauled onto the tug by the heaving line. The deckhand makes the hawser fast to a bitt on the tug’s deck, and now she can pull.

For pushing jobs the tug has a thick pad called a bow fender made of heavy rope hung over the bow. After the fender has been used a while, it gets worn and shaggy and is often called a “beard.” It protects any ship the tug is pushing. There are fenders along each side of a tug, too. Sometimes they are made of rope. Sometimes they are old automobile tires or just logs hung loosely over the side. The logs get so much banging around that they may have to be replaced every few days.

Very often a tug has something on its bridge that looks like a gun. It’s not. It’s a water nozzle attached to a pump, and it’s there to help fight fires on ships.

The kind of tug that you can see on the Mississippi River is called a towboat. She doesn’t tug, and she

doesn’t tow. She just pushes. A Mississippi towboat gets behind a whole string of flat-bottomed barges and shoves them up and down rivers. She often pushes ten barges at a time, loaded with twice as much cargo as an ordinary seagoing freighter can carry.

Many towboats have all of the latest inventions for quick and safe travelling in water that is often more tricky than the open sea. There’s a lot of traffic to watch out for on the Mississippi, and the river sweeps around in many bends. Mud collects on the river bottom, so the captain can’t always know how deep the water is going to be. Uprooted trees and other big things that could damage vessels often come floating downstream. And when it’s pitch dark, or when a thick fog hangs over the water, all these problems get much worse.

Radar is one of the inventions that help towboats avoid danger. Radar sends out radio waves which bounce back to the towboat from anything they hit. In the towboat’s pilothouse is a radarscope, which is a little like a television screen. The returning radio waves show up as spots of light called pips on the radarscope. By looking at the pips, the pilot can locate the shores of the river, other vessels, floating trees and anything else that’s dangerous.

Another wonderful invention, called a depth recorder, tells the pilot how deep the water is under the head barge in his tow. If the river seems to be getting shallow, he can steer the whole tow into safer water. The depth recorder works by sending out sound waves and making a record of them when they bounce back from the river bottom.

In the old days, river craft had a leadman who measured depth with a line tied to a lead weight. Knots and pieces of leather marked the line. Even at night the leadman could tell by feel how deep the water was. For instance, if his fingers felt that the line was wet up to a place where there were two strips of leather, he would know that two fathoms (twelve feet) of water lay underneath. Two markers at two fathoms. “By the mark twain,” the leadman would call out to the captain.

There was once a Mississippi River pilot named Samuel Clemens who, like all pilots, loved to hear that call. It meant that there was enough water to keep his vessel afloat. Later, when he began to write books, he signed them with the name Mark Twain.

In Mark Twain’s time, the Mississippi River boats were driven by huge paddle wheels. As the wood-burning steam engine turned the wheels, the paddles pushed against the water and shoved the boat forward.

Steam engines began working in rivers very quickly after the first successful paddle boat, the Clermont, proved that she could push upstream. River boatmen needed engines more than seafaring men did, because winds seldom blow upstream as they do on the Nile.

Before there were paddleboats, men took cargo down the Mississippi in keelboats. Then they had to get the boats up-river again almost entirely by muscle-power. Pushing against the bottom with poles, or pulling with ropes from the shore, river boatmen worked the whole way up from New Orleans to Pittsburgh.

A river boatman still works hard, but in a very different way. In his time off, he may listen to radio or even watch television on board the towboat. In the old days, he would have caught fish and fried them over a fire built in a pile of sand on the keelboat deck. Today the cook takes food from a freezer, prepares it on an electric range, and stows the dirty dishes in an automatic dishwasher.

In the old days, the river was the quickest way for passengers to travel, and for freight, too. People now go faster by bus or train or plane. But there’s more and more cargo for the barges to carry on the Mississippi and the other rivers that flow into it. Oil, coal, grain, steel, ore, sulfur are some of the things that move along ahead of the powerful streamlined towboats.